Calculations for BTU Loss in OWF Water Line

[Dean186]

I have created this post to help those who have yet to install their Outdoor Wood Furnace and are contemplating their installation.  The calculations were something I ran though before I installed my furnace and it helped me realize just how important it is to have a well insulated water line from house to furnace.

I will be sharing photos of my installation and thought it would be good for others to share information about their water line installation pros and cons.  Photos are always appreciated.

BTUs lost in OWF water line

Facts:

     •   A BTU is defined as amount of heat required to raise the temperature of one pound of liquid water by one degree from 60 to 61 degrees Fahrenheit at a constant
          pressure of one atmosphere
     •   There are 15,200,000 BTUs per cord (4x4x8) of Ponderosa Pine
     •   Central Boiler's TACO 007 pump is estimated at 8 gallons per minute for a typical OWB application (verified with manufacture and it will vary for each installation)
     •   One gallon of water weighs 8.181271 lbs at 150 degrees  Fahrenheit  (8.34 lbs at room temperature)

Calculations:

     •   8 gallons per minute = 65.45 lbs per minute = 3,927 lbs per hour = 94,248 lbs per day
     •   At a total of 1 degree Fahrenheit loss, 1/2 degree each way, in temperature running through the water line and 94,248 lbs per day of water moved; 
          then one would incur:  94,248 BTUs per day of loss
     •   (BTUs in cord of wood / BTUs per day) (15,200,000 / 94,248 = 161 days) or 5 1/2 months (approximately a heating season) to lose the BTUs in one cord of pine.

Conclusion in round numbers:    

     •   There is a heat loss, per season, of one cord of pine wood for every 1 degree Fahrenheit drop in water temperature from furnace to house and back.

[Dean186]

Of course measuring the loss that occurs from the OWB supply side to where the water enters the house is always difficult.  This is because few installations have accurate thermometers installed in the OWB supply line and also have one installed in a manifold at water inlet.  In my opinion, relying on the reading obtained from the furnace control panel and comparing it to a reading inside the house is not a very accurate way of determining heat loss in the water line.

[Dean186]

I have also heard some say, "What's a 5 degree loss when the water is 180 degrees, it's still 175 degrees when it reaches the house".  Well yes the house still gets heated, but if it is really a 5 degrees loss one way, then that is 10 degrees total loss, which equates to 10 cords of wood per season just to heat the earth.

I have also heard, "It's only a few sticks of wood per day" .  If the water line is losing just ½ degree each way, which is 1 cord per year (see above) then this would equate to 3 ½ sticks per day.

Example:  I did a quick count of the number of sticks of wood in one of my cords, which are cut between 18 and 20 inches in length, and came up with 560 sticks per cord.  So if you figure 161 days to a heating season like in the above example, then 3 ½ sticks a day will equal a cord of wood.  I know, too much time on my hands; but interesting numbers none the less.

[Tom_Averwater]

I like your numbers . I never thought of it that way .

[doctorb]

Well done Dean.  Fuel for thought!

[Dean186]

My Thermopex Installation:  Part 1

In the early stages of research for this project I spent a considerable amount of time looking for the best method to transfer heat via water pipe and found, IMO, that Central Boiler offered the best product with their Thermopex dual water line.  This product is made to be installed underground and design to be a standalone product.  However, with 185 degree water circulating continuously through the pipe, there will be some BTUs lost even with the best pipe.

To minimize the BTU loss even more, I decided to surround the Thermopex with 6 inch schedule 40 pipe and insulate the PVC with blue board like it was the main pipe.  The Thermopex would basically be installed in an air plenum. The concern was, can the Thermopex be pulled though a 58 foot length of 6 inch PVC pipe with one large sweep 90 degree elbow and a large sweep 56 degree elbow.  I could not find anyone on the forums that had pulled this pipe though more than just one elbow at the pad.  My Central Boiler dealer and I thought it would be possible.  However, I had a contractor tell me it would not be possible. 

Here are some photos of the PVC pipe in a 30 inch deep trench:



Above is the PVC pipe rounding the house as it goes under the deck.  This elbow was cut from a 90 degree elbow to make a 56 degree bend.



Above is the PVC after blue board was cut to fit and placed on top.



Above is the PVC entering the basement.  One more short piece of blue board and I can cover the pipe.



Above is the PVC coming up through the 5 1/2 inch concrete pad that the furnace will set on.

[Dean186]

My Thermopex Installation Part 2:

The day my dealer delivered the Thermopex, my heart sank when I realized just how inflexible and unruly this pipe is.  We could barely wrestle it into the garage to keep it warm while waiting our attempt at pulling the pipe.   I was only able to flex the pipe an inch when I sat on an eight foot span left in the sun during a test.

I knew it would not be possible to simply pull the pipe by hand.   We needed some mechanical advantage to succeed.  So I went to work building a support system in the basement to mount a winch with a mechanical advantage of 14.2 to 1 and a 1,500 lb capacity.  A half a day later and the winch is mounted to  a 4x6 support platform with a 60 foot strap that will need to be cut and reattached at about 30 feet because the spool is not big  enough to roll up 60 foot of strap.

The winch is rated at 1500 lbs and the strap at 3,300 lbs.  The winch support is made out of 4x6's and braced in three places against the wall and at the top and bottom, to prevent side to side movement.

At last the preparations are complete and I no longer could avoid the inevitable. Today we will attempt to pull the Thermopex through the PVC piping. I hope all my night and days of planning/anxiety/preparation/worry will pay off...

Here are some photos of us wrestling with the Thermopex.



From the outside, I pushed the pipe into the hole with all of my weight while, in the basement, my wife turned the winch with both hands. While we pulled and pushed together, we communicated with a baby monitor (hands free for me outside) and walkie-talkie radio. Slowly, about one foot at a time, we finally succeed in pulling the pipe through and I'm a happy guy!  Hardly able to comprehend that this part, that worried me so much is actually done, I found myself looking at it frequently the rest of the day to be sure we actually were successful.

[Dean186]

My Thermopex Installation Part 3:

I don't know my heat loss, because I never installed thermometers at each end of the water line.  I wish I knew the loss to a 1/10 of degree, but I guess not bad enough for me to install calibrated thermometers.  

However, here is an interesting observation that I made.

Having just got my installation up and running in January of last year, I inserted a temperature probe from my Fluke meter 3 foot into the PVC pipe with the Thermopex installed, but prior to turning the furnace on and then I stuffed insulation around the opening.  I left it for a few days while I was doing other prep work.  I got a steady temperature reading of 45 degrees (the Fluke meter will indicate high, low and average temperature over a period of time).  

After turning the furnace on and letting it run for a week, I went back and inserted the thermometer probe from my Fluke meter again, being careful to not let the probe rest on the Thermopex or PVC wall.   The average and steady reading was 85 degrees.

My thoughts on this:  Insulation just slows the transfer of energy and does not stop it.  If the Thermopex was a perfect insulator the reading would have remained at 45 degrees inside the PVC, since it is not, the temperature went up.  Had the PVC pipe been insulated without loss, then the temperature inside the PVC would eventually rise to the average temperature of the supply and return line, about 175 degrees.  Since neither could be insulated enough to stop the transfer of heat, the temperature inside the pipe settle at 85 degrees.

What I effectively have is my Thermopex installed in an 85 degree, 55 foot long, air plenum that is buried 30 inches down.  

[Holmes]

  Dean186  That is an excellant installation. Now your pipes live in an 85* chase not a 45* ditch.  By far the best way to install the pipes.     Not trying to be funny but you might be saving a cord or more on heat loss. Great job.   Holmes

[Dean186]

First, Thanks Doctorb and Tom for your response.

Holmes,  My savings could be a cord per year.  Even though the installation took a lot of work and additional expense, I believe it was less work than it takes to collect and burn extra wood each year.   Thanks

[ken999]

Great thread Dean.

That's one heck of an installation too. VERY nicely done.

I added some blue board above my T-pex as well as I had very little depth of cover where I crossed my driveway. I also bedded the T-pex in sand and that was all on top of 4" perf pipe and #2 crushed stone wrapped in fabric. I've got alot of water in the ground around here as we are at the base of a decent sized hill with water constantly running at us down the hill on top of the legde rock. I really wanted to keep the T-pex drained and dry, reducing the heat loss from water contact.

So to add to your already great advice, I'll add...Be SURE to mitigate any water problems you have when you install.

[forest]

Nice work ... I am sure there is considerable savings. Insulation within reason is an excellent long term investment. I also really like the pad and brick work. It creates a very esthetic safety barrier. Does the hill in the back effect the draw, or does it matter as much with the fans pushing the air through the system?

[doctorb]

Dean-  let's make a couple of different assumptions.  I am going to round off these numbers.

One cord of oak = 25,000,000 btu's
loss of temp = 2.5 degrees each way (total 5 degrees of loss)

If the pumps push 94,000+ pounds of water per day (round off to 100,000)....
And you lose a total of 5 degrees in transit.....
That means your daily loss is about 500,000 btu's / day.

Therefore, at 25 mil btu's in a cord of oak, it would take 50 days to lose the energy of one cord of oak given an total of 5 degrees of heat loss in transit within the system.  So, I would lose about 3 cords of oak fuel to heat loss over a 150 day heating season.

Are my calculations right?  That's pretty impressive loss for something that doesn't melt the snow on the ground 30" above it.  doctorb

[Dean186]

Doctorb,

Your numbers are correct and I do like rounding them, much easier.
 
My comments on snow melt above pipe:  In the above example, the loss is 500,000 btu per day loss in a pipe that is stretched over 200 feet and buried 30 inches down.  This would calculate to 2,500 BTU per foot per day.   It would take a lot of BTUs to melt the snow on top of the ground from 30 inches down when competing against the outside temperatures acting on the above ground snow and factoring in the surrounding earth that will be absorbing much of that energy.

For thought:  The 8 gallons per minute "fact" that I used in my above calculations for the furnace's pump rating is an estimate and not a measure number.  I wish I had a measured reading to use.  I am sure someone at Central Boiler has real world readings of how much water this pumps move in a "typical" installation.  I asked Central Boiler, but did not get a response.  I emailed TACO and described my installation and stated my pump model number and they emailed me back the figure of 8 gallons per minute.  So, this number will vary from installation to installation.

Dean

[doctorb]

Dean -

Because of the increased distance (300 feet) and increased diameter of my thermopex (1 1/4), I am sure that I have a larger capacity pump than that normally installed.  I remember this was discussed at the time, but I don' t know the exact beefed up size that I have.  If that's the case, then my heat loss in transit is even higher because I move more water than you.

[Dean186]

Great thread Dean.

That's one heck of an installation too. VERY nicely done.

I added some blue board above my T-pex as well as I had very little depth of cover where I crossed my driveway. I also bedded the T-pex in sand and that was all on top of 4" perf pipe and #2 crushed stone wrapped in fabric. I've got alot of water in the ground around here as we are at the base of a decent sized hill with water constantly running at us down the hill on top of the legde rock. I really wanted to keep the T-pex drained and dry, reducing the heat loss from water contact.

So to add to your already great advice, I'll add...Be SURE to mitigate any water problems you have when you install.

Thanks Ken,  

I remember the photos from your installation and the large sheet of blue board over the top of your Thermopex.  It would compliment this post to insert that image showing how you managed any chance of water with all of the sand and the way you wrapped all of it with fabric.    Dean

[Dean186]

Dean -

Because of the increased distance (300 feet) and increased diameter of my thermopex (1 1/4), I am sure that I have a larger capacity pump than that normally installed.  I remember this was discussed at the time, but I don' t know the exact beefed up size that I have.  If that's the case, then my heat loss in transit is even higher because I move more water than you.

Doctorb,

This would be true.  However, don't forget my above comment about using the control panel thermometer reading to determine the temperature of the water existing the furnace.   In my opinion, it would not accurately reflect the water temperature exiting the furnace.  How did you arrive at your numbers?

[doctorb]

The numbers I used were hypothetical.  However, I have thermometers mounted on the inflow and outflow pipes at the back of the stove, and I have thermometers mounted in similar positions in my basement.  So I could get absolute readings.  With the distance of my furnace from my house, I'll bet the heat loss is more than my example illustrates.

[albirk]

Dean I like the way your install lookes and the way everything is around your place (in other pics ) the two large holes one the house the other shop? I like to read what you and doc post lot of good advise one thing on your return water you may not be loosing as much just because of the raidint heat you are getting in your house. One or two cords of is not that big of a deal to me because that is more peaceful time in the timber .

[albirk]

doctorb
what type of wood do you usly burn? my stove and oak don't get along well i have a hard time keeping wood in it i get along better with soft maple,elm,ash and my fav locust

[doctorb]

I use black locust off my own property and oak.  Do you think at your oak burns too fast or does not give off enough heat and thus makes you use more of it?  How dry is the oak?

[beenthere]

I like the red and white oak the best, and as dry as I can get it. Less than two years drying under cover, and there is still too much water in the oak to get good heat from it.
With oak, get good heating of the water, fewest ashes of any wood, and holds a great bed of coals that start the next dry piece easily.
I'm burning white ash now, only because I'm taking them down while the takin is good (and easy).  

For a hot air wood burner, oak may burn too fast and too hot, making it hard to regulate. But for heating water, I think it is the greatest.

[ken999]

Thanks Ken,  

I remember the photos from your installation and the large sheet of blue board over the top of your Thermopex.  It would compliment this post to insert that image showing how you managed any chance of water with all of the sand and the way you wrapped all of it with fabric.    Dean

Here's the thread with my installation pic's.

https://forestryforum.com/board/index.php/topic,40760.0.html

[albirk]

when i burned in the house oak was great held a nice bed of coals like beenthere said but out side i don't seam to get the flame i need to help heat the top of firebox to get the water hot damper will stay open for maybe an hour good fire not a lot of flame so now i sell the oak to buy more toys to take to the timber

[ken999]

What OWB do you have albirk? If your running a E-classic, it's not the top of the firebox you want to get hot, it's the Reaction Chamber underneath.

[ken999]

...Nevermind.... ;D

I just read your other post...CB 5648...totally different animal.

[Dean186]

Ken,  Thanks for the link.  A very effective way to deal with ground water.

Is anyone out there who started with a water line install that didn't work out and changed to a more insulated option?  
Would like to hear about your install if you care to share.

[Eljay]

I installed my Woodmaster 4400 about 5  years ago. The water lines are 1 inch Pex surounder by bubble wrap and inside a 4" coregated PVC pipe. The bottom of the 4 foot deep trench has a 6"layer of sand. The 4" pipe is on top of that and then another 6" of sand. I have always been disppointed to see that the snow would melt over the pipe. Last spring I dug a 4 foot deep french drain to intercept the under ground springs that run after the snow melt. I am sure that these springs run year round but during the spring they cause some basement issues.
So far this winter, I have seen very little evidence of the snow melting over the pipe run. I can only assume that the french drain has helped.
Had I been a little smarter and done some research before the installation, I would certainly have used a better insulated product than what my dealer gave me.

[Brucer]

A comment on insulation in general. First, it will never eliminate heat flow, it just slows it down.

Air is a good insulator, but only if it doesn't move. Glass is a terrible insulator, so is rock, so is polystyrene. The reason fiberglass, rock wool, and styrofoam are all good insulators is because they contain a lot of air trapped between fibers or in bubbles. Water is also a terrible insulator. If you get your insulation wet, the water replaces the air and all of a sudden you've got a heat conductor, not an insulator.

When you have a layer of insulation between two regions with different temperature (e.g., 45 deg and 175 deg), the temperature varies gradually across the layer. This becomes important with snow cover, because light snow is a good insulator (trapped air!). The problem is, snow melts when the temperature rises above freezing.

So you have a heat source under the ground and dry snow on top of it, and the outdoor temperature is well below freezing. The temperature of the ground above the heat source is going to slowly drop as you approach the ground surface. It's going to slowly drop some more as you move up through the snow. The key question is, where does the temperature reach the freezing point?

If the freezing point is in the ground (well-insulated heat source, thin layer of snow) the entire snow layer is below freezing and won't melt.

If the freezing point is inside the snow layer (poorly-insulated heat source, thick layer of snow) then the snow at ground level is going to start to slowly melt.

[hockeyguy]

Dean,
As an electrician who deals with pulling wires through pvc on a regular basis and a homeowner who installed 150' of 1-1/4 Thermopex in a trench,  I can't believe you got that stuff through!
Looks awesome!

[Dean186]

Thanks Hockeyguy,

I cleaned the inside of the pipe and the outside of the Thermopex really well and then I used some electricians grease on the pipe.  I lubed one foot at a time, because if I lubed more than that I couldn't get a hold of the pipe to push and guide it into the hole.   It took us about 45 minutes to complete the 55 foot pull.

Thermopex rigidity demonstrated in photo below:

[Dean186]

Brucer,

You presented some good points.

In an effort to trap the air inside of the 6 inch PVC pipe I made doughnut shaped pieces out of blue board and inserted two of them in each end of the pipe and then capped.  I applied silicone around the outside cap, but not the inside.  After a couple months I removed the indoor cap and slide insulation back to inspect pipe.  Very dry and no problems.

Below is a photo of Thermopex exiting the PVC with cap and just before I applied a bead of silicone.

[Dean186]

I installed my Woodmaster 4400 about 5  years ago. The water lines are 1 inch Pex surounder by bubble wrap and inside a 4" coregated PVC pipe. The bottom of the 4 foot deep trench has a 6"layer of sand. The 4" pipe is on top of that and then another 6" of sand. I have always been disppointed to see that the snow would melt over the pipe. Last spring I dug a 4 foot deep french drain to intercept the under ground springs that run after the snow melt. I am sure that these springs run year round but during the spring they cause some basement issues.
So far this winter, I have seen very little evidence of the snow melting over the pipe run. I can only assume that the french drain has helped.
Had I been a little smarter and done some research before the installation, I would certainly have used a better insulated product than what my dealer gave me.

Eljay,

Thanks for sharing.  Sometimes the deeper the pipe is buried the more chance there is for ground water to come in contact with pipe.  Sounds like the french drain is helping.  Do you know how much of a temperature drop you have in the pipe?

[Eljay]

Dean,

I haven't measured the delta T since installing the French drain. Prior to the French drain I had a 10 degree F delta if the readout on the stove is accurate and actually reflects the boiler temp. I'll take a look tomorrow and get some new data to post.

[Eljay]

I took a look at how I was measuring the differential between the boiler and house and realized that my results are meaningless. I took the reading of the boiler temp from the display. The water temp in the house was from a thermometer inline with the circulating water (hot water baseboard) after the heat exchanger. Obviously this does not reflect the actual temp of the water coming into the house.
My next attempt will be to calibrate two K type thermocouples and read the temp at the boiler outlet and heat exchanger inlet.

Can anyone suggest a good way to attach the thermocouple to the Pex fittings so that an accurate reading is obtained? In the past I have just sandwiched the themocouple between a hose clamp and the Pex fitting. Will surrounding the sandwich with insulation be good enough?

[Eljay]

I was finally able to find the time to get back to measuring the various temperatures in my system. Before doing anything I checked my K type thermocouples in both boiling and ice water. All four were within a degree of the proper temperature. I usedmy Fluke IR thermometer's thermocouple function to read the temperatures. The thermocouples were trapped between a hose clamp and the various inlet and outlet fittings. They were wrapped with fiberglass and foam tape.
With the boiler controller reading 164 deg F
Boiler outlet- 164
Heat exchanger inlet- 156
Heat exchanger outlet-147
Boiler inlet-151
Inline thermometer in circulator manifold-154

I believe that the boiler inlet temp is not measuring the return water temperature but rather it is picking up heat from the boiler.
Interperting the data literaly,it looks as if I am giving up 8 degrees to the ground and 7 degrees to the heat exchanger.
That just doesn't seem right to me. Anyone have a better interpertation?

[Brucer]

I believe that the boiler inlet temp is not measuring the return water temperature but rather it is picking up heat from the boiler.

Not knowing the exact configuration of your system, I can only offer a guess.

You are probably right about the thermocouple picking up heat from the boiler. Insulation doesn't stop heat, it just slows it down. If the thermocouple is on the outside of the Pex, then it will have act as an insulator, however small. That means you won't get a true water temperature reading, but a weighted average between the water and the surrounding air. The more insulation you can apply on top of the thermocouple, the closer the reading will be to the true water temperature.

Here's another way to interpret the data. If the conditions where you measure the boiler outlet and inlet are similar, take the difference between them. That's 13 degrees using your measurements -- the total heat given up in the entire circuit. Now take the difference across the heat exchanger. That's 9 degrees using your measurements -- the total heat given up in the heat exchanger. That leaves you with 4 degrees lost to the environment.

You could try the following. Repeat the measurements and record the values. Then (if you can) wrap a little more insulation around the outside of thermocouples and record the new values. Do they change? If so, you know you are getting closer to the true readings.

[Eljay]

Brucer,

The boiler inlet and outlet thermocouples are attached to the boiler nipples before the pex fittings. Same for the heat exchanger fittings. Maybe I should move the boiler return thermocouple to the compression ring on the pex. That moves it away from the influence of the boiler and may give a truer indication of the return water temp. At any rate,I will take your suggestion and add another few wraps of insulation to all of the thermocouples.

[LAZERDAN]

Great post   I wish I could justify a new installation, just for test purposes.  My story is exactly the same as Eljay  same stove, same install, same water problem,  Night mare.   I did not think of water problem(duah)  Quick remedy, no french drain, too many trees in the woods. I had to dig and install a manhole sump in the backyard, yep have a sump pump ,installed to pump out the trench.   I am loosing 10 degrees and some how this really bothers me.  I have a gut feeling I am using 3-4 cords due to this.  Even if its free wood (its not free)  trucking ,saws,labor,fuel,wear and tear on body, ITS NOT FREE   I would love to just lay thermo pex right on top of the ground for a test, just to put my feeble mind to rest.   Thanks for the info.  At the time I thought it was an exellent install ,its 5 ft down and still will melt snow.  Weak mind strong back.  The oak trees love their warm feet   thanks                          Lazerdan                 Ps  I see on another post you do saving cost  very good , I was'nt cuttin on the free wood analsys just coinscidence and my opinion

[hockeyguy]

Dean186,
Are you supplying hot water to that hot  tub as well as your house?
I know you have an e-classic  with a pretty good size house  and don't remember you talking about supplying the hot tub in previous posts. Looks like a good time. 8)

Also I know C.B only recommends burying thermopex at between 12" and14". Conventional wisdom would lead us to believe that deeper would be better. I wonder if they have groundwater in mind when they give their burial depths?

[Dean186]

Dean186,
Are you supplying hot water to that hot  tub as well as your house?
I know you have an e-classic  with a pretty good size house  and don't remember you talking about supplying the hot tub in previous posts. Looks like a good time. 8)

Also I know C.B only recommends burying thermopex at between 12" and14". Conventional wisdom would lead us to believe that deeper would be better. I wonder if they have groundwater in mind when they give their burial depths?

Hockeyguy,

I installed my hot tub prior to thinking about getting an outside wood burning furnace, so I have no provisions to heat it.  Had I installed the hot top after the furnace install, I would have given serious thought to it.  It would now be difficult to get a heated water line to it with all the concrete.  My extra PVC pipe seen in the photos at the pad was installed for a possible future outbuilding, it goes down into a large sweep 90 degree and out 10 feet to a convenient location.  Gets me away from the concrete pad and brick work if I ever get an outbuilding and if I don't, then maybe I could run a line over to the tube.  Just not sure it's worth it at this point.

My Central Boiler manual recommends a trench depth of 10" to 28" for ThermoPEX and 12" to 14" for Central PEX.  It is also stated; "Historically, lines buried deep (3 to 4 feet) have been found to have a greater number of problems, especially when ground water contacts the water lines".  So, yes to your assumption on ground water being the main reason not to go too deep.

[Dean186]

Below is a photo of the extra run of PVC for future expansion.  The 6 inch and 1 1/4 inch PVC pipe was capped and then covered with dirt.  It's also a good idea to bury plastic marking tape a few inches below the surface and above the pipe.  This makes locating the end of the pipe easier.

This extra run of PVC would be something to consider for those that are in the process of pouring concrete. 

[Dean186]

Once the concrete was poured, I was thankful I took the time to run a second line.

[Dean186]

Below:  Thermopex is installed, pad is done and the ground rod is being driven.  

The concrete pad is large enough to support the new E-Classic 2400 even though I ended up installing the E-Classic 1400.  If we ever get our outbuilding and want to heat it above freezing, I may trade up in size.  My advice for those debating 1400 or 2400; pour a slab of concrete to support the 2400, even if you plan to buy the 1400.  One never knows.

[Dean186]

The photos below show how I insulated the water lines as they enter the Outdoor Furnace

       

[Dean186]

Below is a photo of the Thermopex entering the basement, but not connected. 

         

[Dean186]

Below is the Thermopex connected to heat exchanger and is ready to go.  I insulated the concrete walls, so I did not insulate any of the water lines.

[petefrom bearswamp]

What great info!
Boy I wish I had  this type of information  back in 1994 when I had  a Taylor installed with about 125 ft of buried pex , 30" deep insulated with the black foam split insulation.
I lost 9 to 10 degrees from the furnace to the house and the unit ate so much wood I sold it in the summer of 96 ( it is still in use by my neighbor but leaks badly) and went to oil until '05 when I put a CB 4436 With a run of only 20 feet to my basement. I buried the line 24" deep.
My loss is only 2 to 3 degrees using the temp on the unit and a boiler thermometer in the line before the exchanger  in the basement.
The snow does melt above the line but when I get 2 or 3 feet on it it takes a while but I still must be losing some to the ground.
I wish I had thought of the method described by Dean with the PVC and Blue board.
I concur that the corrugated pipe is a bugger to handle, I tried putting strain on it with my tractor in the hot sun for a few days but to no avail, it still coiled up.
I have an 8 degree differential thru my heat exchanger, but figure that it is just doing it's job,.
Dean I assume you burn softwoods?

[forest]

I know that heat differential is important in the ability of heat to transfer. My question is wouldn't there be a decrease in time as the earth warmed around the pipes decreasing the differential. It would seem that the loss would decrease, unless of course there was mositure in the soil which would greatly increase the surrounding areas ability to shed the heat. Its just a thought. Perhaps just a hopeful one because the loss of three cords of wood just to move the water to the house certainly begins to undermine the reasons for moving the boiler out of the house.

[Brucer]

The earth represents a massive heat sink, at a temperature of roughly 55 Degrees F. As the earth around the buried pipes slowly heats up, the heat bleeds off to the earth further away. The further away you get from the pipes, the greater the mass of earth you have to absorb the heat. You just can't win at the temperatures that an OWB operates at.

The best bet is to keep ground water away from the pipe and pile as much insulation around it as you can.

Ironically, the more heat you extract in your house, the cooler the water returning to the boiler. That return water is physically the closest thing to your hot water feed, so you actually end up bleeding off some heat and sending it back to the boiler :(.

[Just Me]

 Maybe I am reading it wrong, but do your calculations of loss take into account that the lines are not flowing 24 hours in a day?

I my current house with infloor heat it may be an hour between cycles of the heating system. There would be continued loss in the line as the water sat, but it would be on an eliptical curve as the temp difference decreased between the earth and the water in the pipe I would think. This would change your overall loss, assuming that your house does not continually call for heat.

[hockeyguy]

Dean186,
As someone from "The Granite State", I'm jealous of your soil and ease of digging. I can't stick a shovel in the ground without hitting rock or ledge. :'(

[doctorb]

Just Me-

The vast majority of OWB's run their circulating pumps 24/7.  If not, then the backup furnace in your basement might get cool enough to kick on, as no heat would be exchanged while the pump was off.  There could be a theoretical situation where your house thermostats were calling for more heat, and the boiler is sitting nicely at 180 degrees with the pump off, not providing it.  The OWB is not hooked up to your house thermostats, so it doesn't know the temp in your house.  It only knows that it needs to keep the temp of the water inside its water jacket between certain set temps.

When I first looked into an OWB, I mistakenly thought that the water in the outdoor furnace would also be the water running through the baseboard heat in my home.  The heat exchanger keeps these loops separate, and it's a good thing.  So, the circulating pump at the outdoor boiler runs constantly.  CB rec.s that you let it run all year round, even when you are not using the stove in the summer, to prevent sedimentation build up.  I didn't do that.  What do others who do not heat year round do?  Doctorb

[Just Me]

 Ahh....

I did not realize that. My only personal experiance with a wood boiler was an HS Tarm wood/oil that I had in my garage at my ex wifes house. It of course shut off the air supply when it was not calling for heat.

Seems a bit wastefull?

[thecfarm]

Just not to confuse others,but I have a hot air furnace in my basement and it has no idea what the OWB temp is.I always thought the circulators had to run steady so the lines would not freeze. If I would of checked out OWB for 5 years before I built the house,I don't think I would even have a furnace in my house.Takes me quite a few years of looking,comparing and thinking before I part with my money.

[doctorb]

Just Me-

Yes, it may seem a bit wasteful, but realize that this is the same thing an oil furnace routinely does.  It's job is to keep the water jacket at or above a set temp.  When the thermostats call for heat, they start the circulating pumps, not the furnace.  It may seem that they are related because, when the cool water from your system returns to the furnace in your basement, the jacket temp drops and the furnace kicks on.

I believe that you can look at standard oil furnaces the other way.  They have a relatively small volume  water jacket, so it can be quickly heated.  When you call for heat, or hot water, the boiler kicks on immediately rapidly heating this small volume of water.  However, when you need  a lot of heat, this method can not transfer that much energy to the water becasue of the small water volume that's circulating, so the system has to cycle on and off much more often.

The difference is that there is no heat build up time with an oil furnace flame.  When it starts burning, you get high temps right away.   Wood, on the other hand, especially when a fire has been sitting dormant and smoldering to save the fuel, takes a short and somewhat variable amount of time to get up to gasification temps.  Think of it this way.....the standard oil furnace doesn't store a lot of energy awaiting its use.  The OWB, becasue of the delay inherent with getting wood fires up to temp, store a tremendous amount of ready to use energy.  So once they get up to temp, its best to save that energy in the form of a high volume of hot water.

[Dean186]

Pete,

Thanks for sharing information about your install back in 1994.  I had a friend tell me a similar story before I purchased an Outdoor Boiler.  He basically stated; they don't work, don't buy one, they burn way too much wood.  My research found that the installs that weren't working well, were because of high heat loss in the water line, and very inefficient burners were being used.    

Yes, I burn softwood 99 percent of the time.  I have burnt a few loads of hardwood.

Forest,

I have thought the same thing, but as Brucer points out, the increase in temperature around the pipe with 180 degree water running through it vs no water running through it would be small.  There would be a difference none the less.

Just Me,

My calculations are for the water pump running continuously, 24 hours a day.

Looks like Doctorb answered your other questions better than I could have.  I will add that Central Boiler recommends running the water pump continuously.  
 
Doctorb,  I do not run the furnace water pump in the off season.  I hadn't heard of that suggestion.

HockeyGuy,

We have our share of rocks; I just lucked out and had some reasonably good soil in this area.  I was thankful since I dug it all by hand.  Most of the soil up here is decomposed granite.  In this 55 foot run, I used a pick for about 70 percent of the digging.  That was a workout!

thecfarm,

My Central Boiler dealer uses his outdoor furnace as his only source of heat.  He does not have a furnace inside the house.  So, it can be done.

[doctorb]

Oops!  Tried to modify post and ended up quoting myself.  Never mind!  There's no delete button!

[Eljay]

In my last set of temperature readings, I thought that the placement of the thermocouple reading the return water temperature was too close to the boiler and being influenced by the boiler. I have moved the thermocouple to the pex compression  ring and insulated it with more wraps of fiberglass. Here are the latest readings:

Controller reading - 168
Boiler water out      168
Return at boiler       147
Heat exchanger in   160
Heat exchanger out 147

This would indicate I am losing 8 deg from the boiler to the house (65 ft) while maintaning the temperature of the reurn water. I don't think that the 8 degrees I am losing from the boiler to the house can be compared to the 13 degrees I transfer to the house through the heat exchanger since the flow rates are significantly different. The flow rate to and from the boiler is at a maximum of 8 gpm based on Taco's published data. The way my circulator manifold is arranged, there could be 5 Taco pumps contributing to the flow through the heat exchanger. Comments?

[tulenut]

While you obviously slowed transfer of heat to the earth by conduction, while not control the reflective too. Seems you could have done both for max benefit. My wood is all free and dumped by the stove, so I don't and won't sweat over a cord xtra per season, if indeed that's what it works out to be.

[Brucer]

This would indicate I am losing 8 deg from the boiler to the house (65 ft) while maintaning the temperature of the reurn water.

The line to the house will give up heat to the surrounding earth, as well as to the the parallel return line. The return line loses less heat to the earth, and picks up some of the heat lost by the supply line. That may explain the numbers you are seeing.

I don't think that the 8 degrees I am losing from the boiler to the house can be compared to the 13 degrees I transfer to the house through the heat exchanger since the flow rates are significantly different.

I was under the impression that you were taking measurements in the same line: Boiler outlet at the boiler end, HE input at the house end, HE output at the house, and Boiler return. Have I got that wrong?

[Dean186]

In my last set of temperature readings, I thought that the placement of the thermocouple reading the return water temperature was too close to the boiler and being influenced by the boiler. I have moved the thermocouple to the pex compression  ring and insulated it with more wraps of fiberglass. Here are the latest readings:

Controller reading - 168
Boiler water out      168
Return at boiler       147
Heat exchanger in   160
Heat exchanger out 147

This would indicate I am losing 8 deg from the boiler to the house (65 ft) while maintaning the temperature of the reurn water. I don't think that the 8 degrees I am losing from the boiler to the house can be compared to the 13 degrees I transfer to the house through the heat exchanger since the flow rates are significantly different. The flow rate to and from the boiler is at a maximum of 8 gpm based on Taco's published data. The way my circulator manifold is arranged, there could be 5 Taco pumps contributing to the flow through the heat exchanger. Comments?

Interesting readings.  One would need to consider the transfer of energy that happens across the supply line to the return line.  When the house is not demanding energy, the difference in the two lines is less.  It would then be easier to get an accurate reading on potential loss.  The heat exchanger can scrub off 20 degrees during peak demands making the difference in the return and supply lines greater, thus cooling off the supply line water and warming the return water.  

[Dean186]

While you obviously slowed transfer of heat to the earth by conduction, while not control the reflective too. Seems you could have done both for max benefit. My wood is all free and dumped by the stove, so I don't and won't sweat over a cord xtra per season, if indeed that's what it works out to be.

Yes, heat transfer via conduction was slowed via this method.  As far as why not control reflective heat loss; I am not sure how reflective heat loss applies in this case or how I could do anything about it.  Open to suggestions.

While putting up firewood during the summer months, I sweat while collecting those extra cords.  ;)  Just a bit of humor I couldn't resist, I know what you mean.

[Eljay]

Brucer- You do have it right. Maybe I confused the issue with the discussion about the flow rate through the HE. The boiler water flows through one side of the HE while the baseboard water flows through the other side. The two flow rates are probably not the same since my zone circulators are contributing to that flow.
Dean186- I'll see if I can get some readings when the house is not calling for heat. Unfortunately, the way the winter is going so far, that might not be until April.

[Dean186]

Brucer- You do have it right. Maybe I confused the issue with the discussion about the flow rate through the HE. The boiler water flows through one side of the HE while the baseboard water flows through the other side. The two flow rates are probably not the same since my zone circulators are contributing to that flow.
Dean186- I'll see if I can get some readings when the house is not calling for heat. Unfortunately, the way the winter is going so far, that might not be until April.

Eljay, the flow rate is different between my indoor closed system and my outdoor open system.  Different pumps etc... 

I hear what your saying about this winter.  You could just turn the breaker to your indoor furnace off for a few minutes and check it.

[thecfarm]

Dean,I'm confused by your CB dealer has a OWB as his only heat souce.I kinda thought I said the same thing that I would not have a furnace in my house if I would of checked them out more before I had the house built.

[Brucer]

Brucer- You do have it right. Maybe I confused the issue with the discussion about the flow rate through the HE. The boiler water flows through one side of the HE while the baseboard water flows through the other side. The two flow rates are probably not the same since my zone circulators are contributing to that flow.

OK, so it's safe to say that of the 21 degree temperature drop between the boiler outlet and inlet, 8 degrees is being lost in the lines, and 13 degrees is being consumed inside the house. Because the readings are all taken in the same line, the ratio of temperature drops is proportional to the ratio of heat distributed. In other words, the heat exchanger is extracting 13/21 = 62% of the heat and the line to the house loses 8/21 = 38% of the heat.

As far as why not control reflective heat loss; I am not sure how reflective heat loss applies in this case or how I could do anything about it.  Open to suggestions.

I think this is a reference to radiant heat loss. Radiation only comes into play when you have a space filled with a vacuum or with a transparent gas. For example, you'll see bubble wrap with silvered surfaces used as an insulator. The gas inside the bubbles acts as an insulator (the bubbles prevent it from transferring heat by convection). Radiant energy is reduced by the silvering. This doesn't come into play when you're dealing with regular insulation.

[Eljay]

 Quote from Brucer-OK, so it's safe to say that of the 21 degree temperature drop between the boiler outlet and inlet, 8 degrees is being lost in the lines, and 13 degrees is being consumed inside the house. Because the readings are all taken in the same line, the ratio of temperature drops is proportional to the ratio of heat distributed. In other words, the heat exchanger is extracting 13/21 = 62% of the heat and the line to the house loses 8/21 = 38% of the heat.

Brucer- What you say makes sense since all readings pertain to the same line. If what you say is true, then I am truly stunned. I think I once calculated the heat loss in my house at somewhere around 50K btu/hr. That would translate to about a 20K btu/hr heat loss to the ground through the pex. If that is really true, then my 65 ft of insulated 1" pex is a pretty good radiator.
Here in NJ, the design temp for outside air temp is 32 degF. That would make driving force for heat loss 40 deg (72-32). Assuming ground temp at 55 deg and pex temp 170 deg that would make the driving force for heat loss to the ground 115 deg. On the other hand, the driving force to transfer heat through the HE is very small and that is where the bulh of the btus are going. None of this makes any sense to me.
BTW- can someone tell me the correct procedure for including a quote in a post?

[doctorb]

Eljay-

What confuses me about your figures is that you report no heat loss on return to the boiler.  The temp exiting the HE is the same as what's entering your boiler (both are 147), yet you lose 8 degrees between the bolier and the heat exchanger on the incoming "heated" side of the system (168 - 160).  Is there an explanation?   Doctorb

Oh, to quote a post in the same thread you hit the small "quote" box in the upper right of the thread to be quoted.  This opens the standard "reply" box you are used to posting in.  The quote appears in your reply box.  You can add text in front of, behind, or even in the middle of the quote.  You can edit the quote by deleting those portions you don't want to repeat.

[Dean186]

Dean,I'm confused by your CB dealer has a OWB as his only heat souce.I kinda thought I said the same thing that I would not have a furnace in my house if I would of checked them out more before I had the house built.

You did say the same thing.  I was just agreeing that it was possible and giving an example of someone I know that has an OWB as his only heat source.

[Dean186]

What confuses me about your figures is that you report no heat loss on return to the boiler.  The temp exiting the HE is the same as what's entering your boiler (both are 147), yet you lose 8 degrees between the boiler and the heat exchanger on the incoming "heated" side of the system (168 - 160).  Is there an explanation?   Doctorb

An eight degree difference would be hard to explain.  There is some heat exchanged between the supply line and the return line over a long run of Thermpex.  But just guessing here, I would think it would be less than a couple degrees.

[Just Me]

OK, so it's safe to say that of the 21 degree temperature drop between the boiler outlet and inlet, 8 degrees is being lost in the lines, and 13 degrees is being consumed inside the house. Because the readings are all taken in the same line, the ratio of temperature drops is proportional to the ratio of heat distributed. In other words, the heat exchanger is extracting 13/21 = 62% of the heat and the line to the house loses 8/21 = 38% of the heat.


Ok, help me get this straight. The way I am reading this, in practical terms, if I need 20 cords to heat my house a year 7.6 cords were cut split and stacked to heat the ground between my OWB and my house, all other losses aside?

Actually, this pretty much runs with the totals I have been getting from people I ask that either heat with an inside stove or an OWB. Seems to run about a third more for simular homes to have a OWB.

[Eljay]

doctorb- When I initially installed the thrmocouple on the return line at the boiler, I clamped it onto the exit nipple with a hose clamp. I was getting readings that I believe were influenced by the boiler temp in that the water appeared to gain a lot of temp. As a result, I moved the thermocouple to the compression ring of the pex. It may still be influenced by the boiler. I am not sure there is a good place to put it. The only other place would be on the pex itself, several feet from the boiler. I'll try that and see what kind of readings I get.

I am also going to try Dean186's suggestion to turn off the breaker for the house circulators and check the readings. The in and out reading on the heat exchanger should be fairly close. Stay tuned to this station

[doctorb]

Just Me-

A couple of comments combining this and your previous "Low Cost..." thread.

I think you are correct regarding wood consumption.  However, it varies very much with the weather.  In Maryland, we really have only 4 months of full 24/7 heating.  The border months of November and April require less wood.  So wood consumption depends on your climate and how long a period you wish to heat with an OWB as much as it does this issue of heat loss.

I saw your post regarding the regulation of OWB's and your "wake up call" regarding the direction all this regulation is going.  You are very wise to digest all of that prior to making the final decision whether an OWB is right for you or not.  IMO, you have an ideal situation for one and can heat both your shop and your house with it efficiently.  It seems that everything is going to be gasification OWB's by regulation sometime in the future.  If you want to go with a non-gasser, don't wait too long.   Doctorb

[Brucer]

Here in NJ, the design temp for outside air temp is 32 degF. That would make driving force for heat loss 40 deg (72-32). Assuming ground temp at 55 deg and pex temp 170 deg that would make the driving force for heat loss to the ground 115 deg. On the other hand, the driving force to transfer heat through the HE is very small and that is where the bulh of the btus are going. None of this makes any sense to me.
BTW- can someone tell me the correct procedure for including a quote in a post?

Here's a crash course in heat transfer.

1) There's three mechanisms for heat transfer: conduction, convection, and radiation. I'm just going to consider the first one – conduction. That's when heat is transferred through something that isn't able to move – like the insulation in your house, or the ground around your buried pipes. Since you're living in the US, I'll stick to the old fashioned units.

2) The amount of heat conducted between two surfaces depends on three things: the temperature difference between them, the area of the heated surface, and the conductance of whatever is between the surfaces.

Temperature difference is measured in degrees F.
Surface area is measured in square feet.
Conductance is measured in BTU per hour per square foot per degree F.
Heat transferred is measured in BTU per hour.

The amount of heat transferred between two surfaces is calculated as follows:
              Heat Transfered = Temperature x Surface area x Conductance.

Conductance depends on the type of material and the thickness of the material. Metals are very good heat conductors. Foam and fibre insulation are poor conductors. Earth is variable – a lot depends on the moisture content. The thicker the material, the worse the conductance.

3) The pipes from the boiler to the heat exchanger have a surface area measured in tens of square feet. The insulation around them won't have a very high conductance. So even though you have a high temperature difference, the relatively small area and the low conductance will limit the heat loss.

Your house has a heat transfer area measured in thousands of square feet. If it's insulated, the walls will have a very low conductance. In this case it's the large surface area that gives you a higher heat loss.

The heat exchanger probably has a surface area of a few square feet. The conductance will be extremely high (very thin walls, good conductor). The important temperature difference here is the one between the boiler water and whatever it is you're heating. It won't be very much. In this case it's the high conductance that gives you such a high heat transfer rate.

The heat loss calculation from your house is pretty simple but it can be tedious. Things like windows, studs, drafts, etc. mean you have to do a lot of calculations. The heat loss calculations between the buried pipes and the earth are really complicated. If you know the water flow rate through the heat exchanger, the heat transfer calculation is trivial ('cause you can cheat).

One thing that's easy to figure out though. If you cut the length of your supply lines from the OWB in half, you'll cut your heat losses approximately in half. That doesn't help once you've got everything installed :(.

[forest]

Brucer is there a point where the thinkness of the insulation around the pipe would eliminate any heat loss completly, or make it so little as to not really to count. Certainly an R20 wall reduces more heat loss than an R10, but the largest factor is air penetration which is largely controlled by how air tight the vapor barrier is. In terms of the pipe, water would be the factor that could create the greatest loss. If there was no water penetration how many inches of foam would you suggest would eliminate most heat loss?  I suppose it would be different depending on the soil, so lets say sandy soil. J

[Brucer]

Brucer is there a point where the thickness of the insulation around the pipe would eliminate any heat loss completely ...

Nope. No amount of insulation will completely stop heat loss.

The closest you can come is to enclose the pipe in a vacuum. That eliminates all conduction and convection losses. You'd also have to coat both the pipe and the inside of the surrounding tube with reflective coating to prevent radiant heat loss. This is obviously impractical.

On flat surfaces doubling the thickness of the insulation will cut the heat loss in half. Notice that you get diminishing returns by adding insulation. Say you're losing 100 BTU per hour through 1" of insulation. Double that to 2" and you only lose 50 BTU/hr. You saved 50/hr BTU -- not bad. Now double it again to 4" and you only lose 25/hr BTU. But that means you only saved 25 BTU/hr by adding twice as much insulation as you did the last time.

It gets a whole lot more complicated with round surfaces. As you add more insulation, the surface area increases. Thicker insulation reduces heat loss, but greater area increases heat loss. In a concentric pipe, you'd have to increase the insulation by a factor of 4 to cut the heat loss in half.

As you already suggested, keeping the insulation dry is critical. Even foam insulation will absorb water slowly, so you have to be absolutely certain that surface water can't soak down to the insulation. You also have to be sure that ground water won't rise to the level of the pipe. Once the insulation gets wet, you may as well have not put it in.

Best of all is to reduce the length of the pipe. Not very useful advice if you've already installed your boiler -- unless you want to add an extension to your house in the direction of the furnace :D.

[Brucer]

There is a limit to how much you can gain by reducing heat loss through the ground. Here's 4 hypothetical examples of how to burn less wood.

Base Case: OWB efficiency = 50%, heat loss to ground = 40%
10.0   Cords burned
5.0   cords up the chimney
5.0   cords recovered
2.0   cords lost to ground
3.0   cords heat the house.

Case 1: Increase OWB efficiency to 67%, leave heat loss to ground at 40%.   
   
7.5   Cords burned
2.5   cords up the chimney
5.0   cords recovered
2.0   cords lost to ground
3.0   cords heat the house.

Case 2: Reduce ground losses to 20%, OWB efficiency stays at 50%.
7.5   Cords burned
3.8   cords up the chimney
3.8   cords recovered
0.8   cords lost to ground
3.0   cords heat the house.

Case 3: Leave OWB efficiency at 50% and ground losses at 40%, reduce heat loss in house by 25%.
7.5   Cords burned
3.8   cords up the chimney
3.8   cords recovered
1.5   cords lost to ground
2.3   cords heat the house to the same comfort level.

Case 4: Make all three improvements.
4.2   Cords burned
1.4   cords up the chimney
2.8   cords recovered
0.6   cords lost to ground
2.3   cords heat the house.

If you're burning green wood, you can improve your stove efficiency just the by seasoning the wood for a year.

Even if your house is well insulated, if doors and windows don't seal tightly you could lose a lot of heat through infiltration. And even triple glazed windows lose a lot of heat -- tight fitting insulated shutters can make a big difference.

Also, notice how reducing heat loss in the house will reduce heat loss up the chimney and to the ground, even though you don't change the OWB or add insulation to the pipes .

[Just Me]

Brucer

Interesting numbers.

In my last house I built a three sided concrete affair in the basement under the fireplace. It was built tough enough to hold up 30 feet of masonary, so it had a lot of mass. The floor upstairs was 14" thick concrete with a seperate flue running into the fireplace and up to the roof. It kept the fireplace warm at all times and worked very well. I had a 14x21 concrete room in the basement that was sealed to the inside, but wood could be loaded from the outside. I would load it with wood, close the door and throw in a couple of bug bombs. It was just a few steps from the door to the woodstove in the basement. The masonary chimney in the attic was insulated with 2"foam to the sheeting, and the chimney came out the peak just 2', so very little chimney exposed to the cold. It worked well with the exception of the house being 4700 Ft. with 9' ceilings and a lot of glass. Still, the heat bills when we were away from home were quite a bit larger, so I know it was effective. I never had problems with chimney buildup because it stayed warm till the very top.

I have the same options on the house I am building now, and insurance cost are my only real concern. I am checking that out now. The new house is only 1180 ft. Given the losses of a OWB I think I will probably seperate what I do for the shop and the house, and if I can come up with a plan that will not penalize me too much with insurance do a stove/wood furnace in the basement under a concrete floor section again. Most of the heat loss from the chimney can be reclaimed on the way out, there is no transportation losses, as well as no losses around the stove itself. As an added bonus, the wood will be inside. Wood stoves cost less and last longer.

I know many of you have OWB's, But when I look at the numbers and the downsides, I just don't see them as an ideal solution. Cool for sure, but with a small efficient house, there will never be a payoff before the system fails.

[Randy88]

First off I am impressed with the installation and how it went, I am also surprised that you got the line pulled through the pipe after it was buried, now with that said I have several questions that I can't see from the pictures and also something to ponder in thought a while and to tear apart my thinking here.   

The first question I have is did the line flow downhill somewhere that it eventually drained out without any low spots in the line anywhere and that's after settling is taken into account?   

The reason I'm asking is this, I'm a ag drainage tiling contractor as well as many other things and from what I read and have seen first hand, anywhere there's a low spot in the line water will settle out and sit, now unless my thinking is wrong anywhere hot and cold meet condensation occurs and water is an excellent conductor of heat transfer  Now unless there's a  pretty good slope with no low spots on the line where water can sit and pool water will condense around the line and between the outside line causing considerable heat loss, any low spots in the line are going to hold water and with the insulated line it will never get warm enough to evaporate out any excess water.    If theres even one simple low spot and water pools around the line even for a few feet there will be considerable heat loss in the line there and there is virtually no way to see it and it is a constant loss robbing btu's at a larger rate than if it were not inside the tube at all.   

The second question I have is if there is slope in the line how did you get the line elevated off the bottom of the second line to allow for excess moisture to drain out?    If there's nothing holding it up off the bottom of the outside line then how much heat loss is there with the line sitting in water constantly even if its only a fraction of an inch the entire length of the line seeing how water conducts heat loss at a considerably larger rate than just cold dry ground by itself?

I'm not being critical just asking some simple questions that nobody around me could answer or had ever thought of until I asked these same questions.

[Dean186]

Randy,  In response to your questions on PVC slope and condensation.

I designed a very slight slope towards the basement when I installed the PVC pipe.  My thinking was, if there was a leak in the Thermopex, PVC or condensation buildup, the water would not pool and have a way to exit.  I mostly wanted a way to drain the Thermopex if I ever needed to, since the other things were unlikely.  The 6 inch PVC is so rigid it is hard to have a low spot in this short of a run.  However, I put a level to it as I went, to create a very slight slope and no low spots.

The PVC pipe end cap in the basement is removable and I have checked the pipe on three occasions.  No water, no moisture, it is about as dry as it can get in there.  The Thermopex rests on the bottom of the PVC pipe (the best that stiff stuff can anyway).  In some places the Thermopex is up against the sides of the PVC.  With two end caps in place the air inside the PVC is trapped and very very dry.

[Randy88]

Thanks for the response, I was curious and nobody I knew had done it with a slope on the line and then they couldn't tell me if there was condensation or not.     All the insulated tube suppliers around here [thought] it would build up moisture and not to put it in another line, just use direct burial and keep the ground dry by tiling drain tile a short distance away from the line and slightly deeper than the insulated line.   

I don't know if it would make any difference with the state it would be done in or not, the more ground water there is and the yearly rainfall and soil type would matter or not.   As for pvc bending under ground over time, I've seen plenty of it that I've dug up, it will literally bow it into submission without cracking it at all, I've bug it up years later that it has a bow that exceeds a foot or more out of alignment  and it never cracked, just how it can do that is always a wonder to me. 

[Dean186]

I don't know if it would make any difference with the state it would be done in or not, the more ground water there is and the yearly rainfall and soil type would matter or not. 

I don't think it would matter, and except for heat loss, I believe the 6 inch PVC pipe could run through a pond and the condensation inside of the water impermeable pipe would be the same. 

[Randy88]

Maybe if the pipe were capped on both ends and no air movement was allowed, I'm still not sure that would be the case.  Around here they tried the air cooling and heating using ground tempering of the air to either heat it or cool it to 50 degrees, they'd run a line underground and put an intake and riser up away from the building so air could be pulled through and be tempered and the first units that went in were a disaster, they didn't lay the lines to grade and they would pool full of water from condensation and had to be pumped out in order for them to work, later units were installed to grade and those worked nicely but there was also a lot of water running out the lower end no matter what type of tile or pipe was used.   

The lines I've dug up over the years depending on the time of year most pvc lines will have condensation in them from one form or another, either from tempered air entering naturally or from differences in elevation of the line and trapped air can rise and cool or from frost just inside the start of the line as it enters the ground during the winter, there's a lot of reasons to cause condensation but most times even sealed lines will have some in it at some point during the year.

Another question I have is have you ever taken a temp probe from inside the pipe to see what temperature it is inside, or how much heat is given off from the insulated pipe?

I had to dig up one persons line that they tried to ran inside an 8 inch pvc line, the line was already there and had electrical lines running through so they thought they'd just run the new insulated line through but there was a tight bend that they couldn't get it to go through so I was called in to dig it up so the bend could be made more gradual, when we broke into the line we found a lot of water in it and as we put in the shallower bends we also put a tap in it so the excess water could be drained off and into a nearby tile line.   In order for all this to be done we had to pull the electrical lines out and taped it to the insulated line and pulled the entire thing back through before the area was again back filled.    The general consensus from all involved was that the excess water was due to condensation over time and its inability to ever get back out, the water was stale and stunk, so it had been there a long time, there was also frost just inside the start of the line as it entered the ground outside [it was winter out when we did it] even though the line ends were capped at both ends.

[Dean186]

Another question I have is have you ever taken a temp probe from inside the pipe to see what temperature it is inside, or how much heat is given off from the insulated pipe?

The Post has ran long, so you may have missed this from page 1:  

Here is an interesting observation that I made.

Having just got my installation up and running in January of last year, I inserted a temperature probe from my Fluke meter 3 foot into the PVC pipe with the Thermopex installed, but prior to turning the furnace on and then I stuffed insulation around the opening.  I left it for a few days while I was doing other prep work.  I got a steady temperature reading of 45 degrees (the Fluke meter will indicate high, low and average temperature over a period of time).  

After turning the furnace on and letting it run for a week, I went back and inserted the thermometer probe from my Fluke meter again, being careful to not let the probe rest on the Thermopex or PVC wall.   The average and steady reading was 85 degrees.

My thoughts on this:  Insulation just slows the transfer of energy and does not stop it.  If the Thermopex was a perfect insulator the reading would have remained at 45 degrees inside the PVC, since it is not, the temperature went up.  Had the PVC pipe been insulated without loss, then the temperature inside the PVC would eventually rise to the average temperature of the supply and return line, about 175 degrees.  Since neither could be insulated enough to stop the transfer of heat, the temperature inside the pipe settle at 85 degrees.

What I effectively have is my Thermopex installed in an 85 degree, 55 foot long, air plenum that is buried 30 inches down.  

[Dean186]

Randy,  

It sounds like you have experience that I don't have with buried lines.  All I know is the inside of my PVC pipe it is very dry.  

From what I understand you to say, PVC pipe that has been buried for the purpose of running electrical wire and high tech data lines (like fiber optics for our phones and cable TV) could be filled with water in places?  

It would make more sense to me that the water penetrated, the pipes you discussed, from a broken seal or cracked pipe.  

[hockeyguy]

Sorry if this idea has already been mentioned, but I'm wondering if what little heat loss is given off by the thermopex is keeping the inside of the pipe dry.

In 25 years of dealing with underground pvc, I don't think I've ever seen a run without condensation in it. Maybe the t-pex combined with a a low water table is doing it for you.

This is a good thing.

[Dean186]

Sorry if this idea has already been mentioned, but I'm wondering if what little heat loss is given off by the thermopex is keeping the inside of the pipe dry.

The fact that the inside of the PVC pipe is warm and that the outside of the PVC pipe is insulated would make a difference.  Most buried PVC pipe would not have insulation surrounding it, nor would it be heated from the inside.

Upon starting the furnace this year, I checked the inside of the PVC pipe and it was dry.  The furnace had set idle for 5 months (water pump off).

A little condensation certainly would not cause a problem, but I'm glad I don't have to worry about it anyway.

[barkeatr]

Hello,

Im a former CB OWB user, im in the middle of installing a gasification unit to replace it.

Your install is impeccable.  With my CB i had high line loss so I want to tear it up and add more insulation and further decouple my pipe from the earth as you did.

I have gone through the thread a few times..have you been able to record your line loss? I assume it would be very low with your installation.

thanks for posting your work.

barkeater

[Dean186]

Hello,

I'm a former CB OWB user, I'm in the middle of installing a gasification unit to replace it.

Your install is impeccable.  With my CB i had high line loss so I want to tear it up and add more insulation and further decouple my pipe from the earth as you did.

I have gone through the thread a few times..have you been able to record your line loss? I assume it would be very low with your installation.

thanks for posting your work.

barkeater

Thanks and your welcome.   I was hoping that some new installers would benefit from my notes.  I do not know my line loss because it would take calibrated thermometer at each end of the pipe, which I do not have installed.  

I have read of several methods of reducing heat loss in water lines and PVC pipe is not the only way to help with loss.  I think one should start with the best pipe and in my opinion the Thermopex is very good.  I'm not a dealer for Thermopex or associated in any way with the product.  I think good drainage is the next most important step and then additional insulation.  Blue board works well, and I have heard of the heavy weight spray foam.  I personnel don't know how spray foam holds up over the long haul.  There are many more knowledgeable persons than I on this forum, who would know about spray foam for underground usage.  

Blue board is relatively inexpensive and easy to install around the thermopex.  The extra work and expense taken during installation will pay off later.

Best of luck with your installation and feel free to put up some photos.

[Holmes]

Dean186  You are right about the blue insulation, and the pink stuff is the same. Everyone should know that FOIL FACE  insulation board should not be used under ground. Is does not hold up , absorbs moisture and can become a nice ant farm. Holmes

[Dean186]

Thanks Holmes,  I knew the blue & pink board was the right stuff, but did not know about the foil face board breaking down.   It isn't rated for that application, so best not to use it.

Does the spray foam that some have used to cover their pipe, which gets covered by dirt, hold up over time?

[Holmes]

Dean  The 2 lb density r6.8 does hold up( urethane foam ) . Regular 1/2 lb density icynene  does not. I used the urethane on the inside of my stone foundation and see no signs of it breaking down. They used to spray it on the outside of foundations when they wanted to use the space inside as a living area.  Holmes