Heat recovery from indoor exhaust piping-pellet stove

[Jake86]

Is it possible to recover some of the heat loss from one's exhaust piping before it all goes up the flue? For example, using plumbers metal tape wrapped accordion style around the circumference of the exposed exhaust pipe, thus increasing the heated exhaust area. This acts similar to the heat exchanger in the pellet stove itself. I understand that this heat removed from the exhaust will lower the temperature of the flue gases through the stove piping which can affect draft, but since a pellet stove uses a forced hot air exhaust fan to expel fumes the draft should not be significantly affected. I could see this increasing the efficiency of a pellet stove significantly, depending on the exposed indoor piping.

 

[alternativeheat]

Is it possible to recover some of the heat loss from one's exhaust piping before it all goes up the flue? For example, using plumbers metal tape wrapped accordion style around the circumference of the exposed exhaust pipe, thus increasing the heated exhaust area. This acts similar to the heat exchanger in the pellet stove itself. I understand that this heat removed from the exhaust will lower the temperature of the flue gases through the stove piping which can affect draft, but since a pellet stove uses a forced hot air exhaust fan to expel fumes the draft should not be significantly affected. I could see this increasing the efficiency of a pellet stove significantly, depending on the exposed indoor piping.

I think this gets asked every year. Seems to me is that you need some sort of official exchanger device because of the double wall pipe that pellet stoves use. You need something that will contact that inner pipe to get any real benefit from it. The outer pipe may be uncomfortable to touch but you can touch it, the inner one is more like 300 deg F and on a Harman running full bore it could hit 500 deg.f. You're not touching anything that hot for long or you would stick to it and get fried.. So best of luck with your experiment. Granted not all stoves run this hot and at times neither do Harman's. But just sayin.

 

[Lake Girl]

Jake, lower exhaust temps would be more of a problem ... they create creosote.

 

[Bioburner]

And mine will nearly freeze shut with water vapor on the Bixby with its outer wall intake system if the temps get real cold for to long. But that stove monitors exhaust temps and ramps up room fan to not let to hot of exhaust go out the stove. Smarter stove with larger room fan and exchanger is the answer to high exhaust temps IMO.

 

[Lake Girl]

The change I have seen that seemed to be somewhat successful was an addition in the heat exhange tubes ... Quadrafire stove was the stove I think. Found it https://www.hearth.com/talk/threads/quadrafire-castile-experiment.58216/

 

[Bioburner]

There was a thread on turbulators. I know they use them on larger boiler tubes. See many used in old thrashing machine engines.

 

[rich2500]

interesting logic but sounds like much more hassle then it's worth on double wall pipe.

 

[Jake86]

Jake, lower exhaust temps would be more of a problem ... they create creosote.

Maybe the double wall exhaust piping would limit this problem. I used the above method (metal tape folded accordion style) on my son's gas exhaust piping a while back and we both noticed a definite heat increase in the mud room/furnace room. The natural gas furnace had six inch exhaust piping. The draft did not seem to be affected negligently. It is a lot of work though.I measured the temperature of my pellet stove exhaust piping @approximately 120 degrees. Maybe not worth it?

 

[Lake Girl]

Well, if you go for it, document before and after and try to quantify the temp changes.