Outdoor wood heater plumbing question

[woodmills1]

My house is a heat monster

before the wood furnace front of house would get to 70 middle to 64 and back to 60 for way too much money

On my third winter with my outdoor wood furnace and front is 74 middle 68 but back only 62-63.  Quality wood and constant fire attention don't change this when cold/windy.

I think I hit on one reason why I am not getting enough performance from my system

My set up is: the water leaves the furnace outside and goes to the water to water heat exchanger on the hot water heater, then to the water to air heat exchanger at my oil burning furnace, then to a stand alone heating unit with its own heat exchanger and fan, then back to the furnace.  The stand alone unit is in a side addition that had its own propane heater to keep it warm.

OK, here is what I have figured may be giving me a problem.  All of the piping from furnace and back is 1" pex except for the stand alone unit.  It is 1/2" copper.  The stand alone unit is in the loop and not on a side branch.  I am thinking that this is causing a flow restriction, such that the other two exchangers are not working to their capacity.


So, do you think this is a problem, and if it is, do I add a balance tube to allow bypass or should I seperate out the stand alone unit on a loop of its own?

[sprucebunny]

The flow of the whole loop is reduced to the potential of the 1/2"

Put a seperate loop to the radiator and you will have much more heat  8)

[woodmills1]

do you think I could put a link between the 1 inch just in front of the 1/2" with the same result?

[sprucebunny]

What kind of 'link' ???

There used to be a fitting that would split your flow and had a directional scoop in it to keep the water moving to the radiator. Not sure if it's still made... I'll ask the Master plumber tomorrow.
Another possibility would be a higher volume circulator for that circuit.

[woodmills1]

my thinking is the pump has enough flow to supply both so if I put in a bypass the first two exchangers will get the flow they need and the last 1/2" one won't get scavenged.

[Dana]

If you have a large enough flow using one pump then I would just install a tee in the line before the water heater and the oil furnace and run from there to the stand alone.

You may need a check valve or two in the return line to direct the flow? I know on my C.B. stove I installed the check valves on the side of the stove.

Are you using any zone valves to control the heat? This would also be an option. The way its plumbed now I think you have removed most of the heat from the water by the time its left the oil furnace.

[farmerdoug]

I think Dana has hit upon your problem.  You are expecting to much heat from the water flow.  The 1/2 pipe is restricting the flow too.  You could add an second line for the water heater and the small heat exchanger but I am not sure this is an option for you.  You do not state the overall lenght of run of your water line.  One option is to move up to a larger pump for more volume.  As for the bypass, I would install it and put in an valve so you could restrict the flow so you get enough water through your radiator.

Farmerdoug

[sprucebunny]

  You are expecting to much heat from the water flow.   

The T is called a Monoflow. Available in 3/4 x 1/2 and 1 x 1/2. You only need one on the incoming end.
You will get much more heat if the 'stand alone unit' is on it's own loop. If it is a radiator of some type, with many small pipes and fins, they will slow down the flow considerably because of friction.

[SPIKER]

I think you have a design issue.  not just the 1/2" but throughout the system

the system should be setup so that each area is a separate zone.   valves and or pumps can do this

the main pump should be circulating water from outside boiler to house and back through T's all 1" and 1" back to outside boiler too.  each zone needs 2 T's one in HOT side and one in Return/COLD side of the 1" PEX going/coming from boiler.

use a smaller pump T'ed into this LOOP for each ZONE (hot water heater, furnace and aux heat blower)  that is 3 pumps, easy buy from e-bay or local should be less than $50 or so per pump ad in some thermostats capable of turning on/off the pumps for each zone probably $50 each or less.   

SO for the 3 zones look to spend ~300 bucks but the performance will be well worth it.  a 4th thermostat can turn on/off the main pump or use relays so that any ONE zone calling for heat will turn ON the main pump and if NO zones are calling for heat then the main pump can be off.  this can/could/should be integrated with the boiler now?

anyhow when any zone calls for heat, the pump for that zone turns ON pumping hot water through the zone and back to the return boiler line.   when the zone does not need heat the pump shuts off and the pump restriction keeps most of the hot water simply circulating back to the boiler.   this can be done using Solenoid Valves too but the pumps are a more positive design...   the Solenoid valves depends on the main pump to push the hot water all way though the system and depending on the design this may be too much restriction and or distance to make the system perform well.

I forgot to mention that you can also use a 3 way valves for the zone control so that one valve takes priority over the main flow so no extra pumps are needed.   in this type of setup, the valve turns ON and flow is diverted through the valve into zone X and back to return.    return can be continue down line to rest of zones OR back into the main return to boiler.   If you plumb it back into main line then every thing will share fixed volume of flow set by combination of the restrictive zones/device as it is setup now.   plumbing it back to return will cut off all down stream zones from getting any flow/heat until the heat/temp is reached in the first ON zone.

the 3 way valve can also be a motorized valve which controls the 3 way valve to only let a small flow into the zone wanting heat.  the rest bypasses the zone continuing down the line.

warning though the valves are expensive and can be more expensive than the pumps if you don't shop around.   I have 4 pumps at home all same/similar design that are going to be used for zone control.   I think I ended up getting these at 2 different auctions from e-bay,  one set was 35 bucks each the other set was like 45 each.

anyhow these are for full HEAT (180 degree F water) if you are going to use in-floor radiant heat then you need to MIX hot & cold water so that the floor heat is ~86 degrees F NOT 180 F as that can cause problems.   it is worked same way only you use the feed pump to put HOT water into the loop slowly (back up pressure / flow giog into the floor) let the floor loop go out into return through some resistance (water valve/ partly closed ball valve ect) and have a small hot water pressure vessel in the loop line.  monitoring the temp of the return loop is late you need to use the feed loop so that you don't end up with too hot of loop temp..


mark M

[woodmills1]

thanks for all the tips, I have sorted out the problem and this week it was warm enough to drain the stove and do the fix.

I called the company and they were surprised that i was instructed to install the on the wall heater in the complete loop.  I was told it needed to be separated out using two diverter T's.  I believe these are the monoflow T's that sprucebunny mentioned.  I bought two of them and put them in.  It took a little burping to get water through the on the wall unit, but all is well.

Though it isn't real cold out yet the difference is very noticable.  The stove isnt working as hard, and wood use seems to be down.  Will know better as it gets colder.  The air temp at the farthest end of my duct run is 115 degrees.

On a side note I couldnt get the on the wall unit to read the correct room temp after the work was done.  Turns out the temp sensing thermister wire was on the bottem og the unit just above the newly installed copper.  It though it was 86 degrees in the room.  Had to insulate the pipes. :D :D :D Now it works well.

[sprucebunny]

Glad to hear you got it working better.

Still gonna be some winter around here .... I hope.