Recirculating chimney exhaust back into stove for more heat?

ethanh100

New Member
Jul 4, 2019
2
CT
Hello,
I have a wood stove that I use as a pool heater, and basically works as a normal wood stove, but has tubing above where the fire burns that the water runs through to be heated. While this works pretty well and with a good fire burning I am able to get a temperature delta of around 8 degrees Fahrenheit, it could be a lot more efficient.

Out of the top of the chimney, there is still tons of hot air that comes out, so there is so much more potential for that heat to be transferred to the water. I was trying to think of some ways to increase the absorption of heat, without adding more tubing or radiators.

Would it at all work if I were to take, say half the volume of the exhaust from the fire and re-route it back into air inlet? This obviously would increase the amount of passes the heat has over the water, but would it totally just kill the efficiency of the fire, maybe even put it out?
Obviously this wouldn't be the quickest way to heat the water as the fire would burn slower, so I would use such a method when I need to heat quickly.

So would this work or no? Does anyone have any other ideas on how to increase my efficiency? Thanks!!
 

Dug8498

Feeling the Heat
Jun 20, 2018
259
Southern NH
Do you have any pics of this setup?


Sent from my iPhone using Tapatalk
 
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ethanh100

New Member
Jul 4, 2019
2
CT
I dont have pictures of my exact setup, but can find some very similar ones online. Its basically a vertical rectangular prism, with the bottom section being where the logs burn and the top half being where the tubing runs. and then a chimney stack. I was pretty much just thinking getting a dryer hose that was half the diameter of the chimney and routing it into the door.

wood-burning-pool-heater.jpg
 
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begreen

Mooderator
Staff member
Nov 18, 2005
79,281
South Puget Sound, WA
Agreed that these setups look pretty inefficient with a lot of heat lost up the stack and perhaps no secondary combustion. A reburn system would help, but not as described using dryer vent.
 
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barnaclebob

Member
Nov 29, 2017
229
Puget Sound
If higher water temps are your goal then there are only two ways to get the water warmer but you said you don't want to add more tubing or radiators so really # 2 is out.

1. Increase the fire temp. Recirculating the exhaust wont help that because you would be reducing the amount of oxygen to the stove. Maybe try using smaller splits that burn faster and hotter?
2. Improve the efficiency of the heat exchanger. Instead of recirulating the exhaust you could try to extract more heat from it via a secondary heat exchanger. Run the cold water through a radiator of some kind which is heated by the stove exhaust before it goes into the hotter primary heat exchanger inside the stove. But if your exhaust it colder it could reduce your draft which will make the fire burn colder.
 

brenndatomu

Minister of Fire
Aug 21, 2013
4,259
NE Ohio
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