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Wrap a water line around pellet stove chimney & flow that heat into whole-house hyd. sys?

-I'm looking to wrap a 3/8" copper line around a double-lined pellet stove chimney (in basement) and tap it into the 'wild' line of whole-house hydronic heating system (which runs right above my pellet stove)
-Since it's only 3/8", and the hydronic 'wild' line is 3/4", I plan to install a ball valve so that 'some' of the luke warm return water in the 'wild' line still feeds along it's normal path, while picking up 100% of the hot water off the new 3/8" copper coiled around chimney.
-My main Question: as long as the main (only) circulator pump is running 100% of the time that pellet stove is lit, and as long as I allow some supplement 'cool' water to flow with the 3/8th" pellet-heated water, is there any additional risk in doing this (add'l expansion tank needed near pellet stove, etc.)?
-Seperate Question (wiring): How to keep the main (only) boiler circulator pump running 100% of the time the pellet stove is running and ALSO have it operate 'as needed' (normally) with the propane boiler. (a three-year old Weil-McClain Evergreen 155). That would be ideal. 2nd best option is to direct wire the pump so that whenever I turn on the main power to the boiler, it turns on the pump (we run the pellet stove almost non-stop from Nov-Mch). If I don't have the pellet stove firing, then I can just bypass the water flow from the new coil around the chimney...no need heating the chimney! ...Big drawback is I'd have to remember to open that 3/8" coil line, prior to firing the pellet stove...not a wise setup I'm sure.


  • sprranger
    sprranger Member Posts: 2
    Please disregard that last sentence. As long as I drain the water from the 3/8" coil, when bypassing it, and leave the drain open (so as not to build up a steam bomb), then I guess this isn't as bad as I stated, but still sounds a little complicated for the next homeowner, etc.
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,549
    Hi, It's a bit off topic, but how much heat is available through double wall vent pipe? Is there enough heat to justify building this? Should I assume that you're trying to get heat from the stove to the far reaches of the house? Might it be simpler to do this with warm air? Questions! :p

    Yours, Larry
  • Jamie Hall
    Jamie Hall Member Posts: 18,953
    Don't do it. Yes, you will get a small amount of heat off the stove pipe -- though on double wall it will be precious little.


    You will cool at least to some extent the smoke from the stove. This will allow creosote to build up in the stove pipe (and chimney?). This will increase, if not actually guarantee, a chimney fire, and trust me -- those are just no fun at all.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GroundUp
    GroundUp Member Posts: 1,406
    You'll spend more on electricity spinning that pump than you'd spend just creating electric resistance heating, and are substantially raising the possibility of a chimney fire. Please do not do this
  • psb75
    psb75 Member Posts: 570
    Sounds kind of wacky. Save yourself the fuss and trouble. Don't do it.
    I have done this for others, the coil around the smoke pipe and it didn't go well.
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 15,988
    This brings me back to the '70s. What seemed like good ideas didn't work out so well for many.
    Retired and loving it.
  • Derheatmeister
    Derheatmeister Member Posts: 1,280
    This setup is called an "Economiser" it can be done,but as stated above you will have to be careful about the setup.
    1. Double and triple wall is made so that it reduces the heat transfer to the outside wall of the vent pipe in order to be close to combustiables surfaces and keep the heat in the vent for drafting purposives...So using a double wall pipe will greatly reduce any energy that can be "Harvested"
    2. Even If you used a heavy gauge SS single wall vent pipe and wraped the copper coil around it,then installed a "Asbestos" type of insulation around it to be covered by a steel vent pipe it would be advisable to intergrate a sensor on the exhaust upstream from the economiser to make sure that the flow rate of the exstraction pipe is Reduced when the flue temperature is to low in order to prevent Creosote buildup/Flue gas condensation/Corrosion or even an Carbon Monoxide spill.
    3. It would be advisable to use a storage tank/reliefvalve/expansion tank and a PWM driven circulating pump for this setup
    4. It would be advisable to use a Gravity type unloading valve in case of a power failure..Then again i guess that a small None water jacketed pellet stove would also not operate during a power failure and the pellet stoves venting system would not have that much heat to get rid of.
    5. Any energy havested into the tank should be exstracted/injected into the heating system via a control that is based on outdoor reset curve.for exsample a Tekmar 356.
    6. Of course some of this can also be done without fancy controls for exsample using Analoge/Bimetal/Mixing valves/gravity setups/Old school 1970 ties off grid/Dead men setups.,,but it will take an expert to set it up and maintain it.
    Sooo..Yes it has an can be done but it in some instances it may not be worth it.
  • Mike_Breault
    Mike_Breault Member Posts: 36
    cooling Flue gasses has dangers in Creosote buildup.

    as mentioned by many probabaly not a good idea, and minimal return