Exhaust to Water Heat Exchanger

I wasn’t able to get any footage of installing the exhaust to water heat exchanger, but I did manage to take a picture of what the first two stages look like inside of some uninsulated stovepipe. Note how the stages offset:

Exhaust to Water Heat Exchanger
Exhaust to Water Heat Exchanger

The offsets make the exhaust snake through the stovepipe, further aiding in efficient heat transfer. This video shows how I insulated the stovepipe as well as how the plumbing system will work:

I have test fired it to be sure the downdraft works. The first run was very successful in spite of having fairly wet, punky wood. It did take about 30 minutes before it ran smokeless, but I’m hoping that adding a tiny bit more of primary air and having better fuel will shorten that time dramatically.

Once it reached operating temperature, the exhaust ran clear and odorless. I recorded a maximum of almost 80k BTU of actual heat being transferred to the water. When I have good wood to work with, I’ll be able to calculate how many BTU of wood is being burned and get a good idea of overall efficiency.

On a huge positive note, at that peak BTU production, I only measured the exhaust to be 145*F, meaning I’m pulling the vast majority of the heat out of the exhaust. I do wonder if having potentially condensing exhaust could become a problem. Time will tell.

Not much is left to do on this project. I need to install a rope gasket on the door, build a shed around the stove, and insulate it with mineral wool for maximum efficiency.

Tomorrow, I’ll release a video showing how I purge the air out of the plumbing system.

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