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Outdoor Wood Boiler Plumbing Question

Started by Bob Lentz, January 30, 2023, 09:35:18 AM

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Bob Lentz

The circulating pump on my central boiler runs 24/7.  I was wondering if it would be better to have the circulating pump only turn on when the circulating pump for my whole house turns on. I am curious as i couldn't understand why my OWB water temp was falling with no demand - i can see all my thermostats online and none were calling for heat.


In doing this, one would have to put another sensor in place to turn on the curculating pump in the OWB if the OWB water temp falls below 100 degress (for freeze protection).

Thoughts?
eClassic-2400
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Heating 6500 sqft house and small pool

PoginyHill

I'm sure it can be done. Where could your heat loss be if you can see temp drop with no zones in the house calling? Mine stays rock steady with no demand. But normally, at least in colder weather there is something calling in the house. For me the only savings would be electricity for the circulator - which wouldn't be enough to buy the components for the additional controls. I'd be curious where your heat is going with no house load.
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beenthere

QuoteThe circulating pump on my central boiler runs 24/7.

Where does the water circulate to ? the house and back?

Quote

In doing this, one would have to put another sensor in place to turn on the curculating pump in the OWB if the OWB water temp falls below 100 degress (for freeze protection).

I have such a sensor, and for shipping cost I will send it to you. Removed it from my in-house wood boiler system. Used it to kick on the gas boiler if the wood fire couldn't keep up at least 100° water temp. PM address if interested. 



 





 
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PoginyHill

In my case, yes - through a plate heat exchanger in the house. I think most set-ups will have some sort of a heat exchanger in the house, giving up heat when there is flow on the other side of the exchanger.
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petefrom bearswamp

Mine goes thru a plate exchanger into the oil boiler jacket thence to the 5 zones.
Main circulator pump only runs when a zone turns on.
Cant remember how I wired it tho.
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hedgerow

PoginyHill    One thought. Is your insulation on your under ground pipe bad? You could be pumping a lot of heat into the ground. I have all my pumps set up on my Garn to only turn on when a system is calling for heat. I felt like when I built my system there was no reason to have a pump running unless something was calling for heat. 

Gearbox

If it dosn't run continuously when it does kick on you will put a lot of cold water back into your system. When I start my outside boiler in the fall it is a wood pig for the first week . even with the best insul pex it still has to warm up the ground around the pipes . the earth is only a R6 and the power draw is like 3 or 4 light bulbs 
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Bob Lentz

my run from boiler to heat exchanger is only 10ft.  Total loop of 20ft round trip.
I have heavy duty insulated pex - i cant for the life of me figure out what is drawing the water temp down when there is no call for heat. Runing that short of loop when no water is moving on the other side of the heat exchanger should not cause a drastic loss of heat.

What about the fill port on the top of the boiler - could it be causing cold air to infiltrate the water tank?

eClassic-2400
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Heating 6500 sqft house and small pool

Gearbox

I wonder if you have water in your insulation around the Pex . mine has caps to keep the water out of the insulpex 
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rusticretreater

I would check the tank temp to make sure the thermostat is working correctly, then compare that to the temp at the pump outlet, the intake of the heat exchanger, the exit of the heat exchanger and the temp returning to the tank.  That will tell you where your losses are occuring.  Its probably more than one spot.

As noted, if you are not running it constantly you will end up with an entire run of cold water coming back to your tank when you start circulation.
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Corley5

The insulation around the boiler itself isn't compromised?
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PoginyHill

Quote from: Bob Lentz on January 30, 2023, 06:04:44 PMi cant for the life of me figure out what is drawing the water temp down when there is no call for heat. Runing that short of loop when no water is moving on the other side of the heat exchanger should not cause a drastic loss of heat.


Is it possible for one of your zones (on the other side of the heat exchanger) to be flowing by natural circulation? If there is a check valve stuck open that could happen. If you know that no zones have been calling for a while, say an hour, are any of your pipes warm? 
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chet

@Bob Lentz  What is the time frame and the amount of heat loss you are having? Also what kind of connection do you have for that pool, and is it heated continuously?
I am a true TREE HUGGER, if I didnt I would fall out!  chet the RETIRED arborist

NE Woodburner

Feel the pipes for each zone that should not be calling for heat. I used to run an indoor wood boiler and had an issue with one zone always being hot even when the thermostat for that zone was not calling for heat. I didn't care so much about the little bit of extra wood I may be burning, but that zone was so hot that we had to open windows all the time. I finally had a buddy with HVAC knowledge take a look at it for me and he determined that the circulator pump running between the wood and oil boilers was pushing hot water past the circulator pump on the offending zone. We throttled back a ball valve in the line that ran between boilers until we couldn't feel heat on the pipe in the offending zone and I never had an issue again for the many years I ran that boiler.

Corley5

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OH_Varmntr

Quote from: Bob Lentz on January 30, 2023, 06:04:44 PM
my run from boiler to heat exchanger is only 10ft.  Total loop of 20ft round trip.
I have heavy duty insulated pex - i cant for the life of me figure out what is drawing the water temp down when there is no call for heat. Runing that short of loop when no water is moving on the other side of the heat exchanger should not cause a drastic loss of heat.

What about the fill port on the top of the boiler - could it be causing cold air to infiltrate the water tank?



What do you consider drastic?  Is this something new that you've been experiencing?  Can you quantify the loss?

You assume that no water is moving on the secondary side of the HX (brazed-plate HX, I suppose?).  Even if no flow is assumed to be generated on the secondary by means of a circulator, there is enough heat being exchanged that a thermosiphon could be generating flow through a zone.  

These systems are usually designed to prevent this via check or zone valves.  Some circulators have check valves in them.  My Taco circulators I used on my zones had white plastic checks that snapped in to the output side of the flanges.  If yours does, it may be stuck open.

As far as running the main circulator boiler intermittently, it needs to run constantly to prevent cold zones in your boiler tank.  That's why it pulls the hot supply from the top of the water jacket and returns it lower in the water jacket.  

I ran a CB6048 with 75-feet of the insulated ThermoPex and 400-gallons of indoor storage for 5 years.  Ended up getting rid of it because no matter what I seemed to do, they are just really inefficient.


chet

@Bob Lentz  He musta figured it out as he hasn't been back online since 1/30.
I am a true TREE HUGGER, if I didnt I would fall out!  chet the RETIRED arborist

chet

I'd still like to know what cured his problem.   :-\
I am a true TREE HUGGER, if I didnt I would fall out!  chet the RETIRED arborist

Bob Lentz

All, been a while - busy winter/spring - anyway now that summer is here, i am still scratching my head as to the amount of "Demand" on my boiler.  All have checked all 16 of my zone vales and none are stuck open. All my thermostats are WIFI so i can "see" what is calling for heat other than domestic hot water.

So in the middle of the night, with zero house demand, no domest hot water demand and no pool demand, i watched my water temp drop 10 degrees repeatedly (several cycles) in about 20 minutes.  That's crazy!  With only the water circulating through the CB Side and no demand, i would think that CB tank would maintain temp for longer that 20 minutes.
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Heating 6500 sqft house and small pool

PoginyHill

No warm pipes on the other side of the heat exchanger at all? Indicating a leaking zone valve and natural circulation....
I have 250 ft of 1-1/4" pipe (125ft supply and return) going to a plate heat exchanger. With no demand, my boiler temp actually rises a bit until the fire dies down, but does not drop noticeably over hours if there is truly no demand.
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Bob Lentz

well, i monitored all that from the comfort of my bed LOL - i would need to go down to mechanical room and feel the pipes - will do that for sure and update you all.
eClassic-2400
Triangle Tube Backup (Propane)
Heating 6500 sqft house and small pool

rusticretreater

I would verify that the temp shown in your software equals the temp the water is at.  Especially after a temp drop.  I think it might be wonky sensors. 
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hedgerow

Bob If nothing is calling for heat it should hold better. I would go to your mech room and feel all the pipe's to see if something is running. I had a relay with the points stuck on my domestic water pump keeping the pump running even when my domestic wasn't calling for heat. My Garn was doing the same thing. I was losing temp and nothing calling for heat. Replaced the relay and problem was gone.  

Bob Lentz

Update - i went and re-checked my plumbing around the heat exchanger - low and behold, there was a grundfoss pump that ran 24/7 on the internal loop of the house!  So, this pump was circulating water around the house but not going to any zones - so about 40 linear ft of copper loop in the mechanial room, and another 80 linear ft of copper to the zone valve manifold on the 2nd floor.   I am going to re-wire the pump to only run when the main circulating pump for the house comes on.  Hard to believe that 150ft of copper would cause that much heat loss - we fill find out!

Thanks for all the input gang - i really appreciate it.
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Heating 6500 sqft house and small pool

trapper

Running one copper pipe around the ceiling of my basement will raise the tempeture of the main floor rooms 3 degree so I bypass it in the summer and only run the hot water through the sidearm on the water heater.
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