Hello Permies,
Long time lurker, rare poster.
I saw an interesting article today that Finland built the world's largest sand battery to store energy. It reminded me of something my Dad built back in the 80's. I did a little searching and could not find it by the name I remembered it called, but it was Nordic/Scandinavian and it was pronounced "hah-suh". Doing a few web searches, I tried many spellings (hassa, hasse, huhsa, etc.) but did find an old Mother Earth News article that didn't use the name, but described it completely.
https://www.motherearthnews.com/sustainable-living/renewable-energy/outdoor-wood-burning-furnaces-zmaz77zbon/. I rarely post, but didn't find anything like this in the forum and thought it was worth sharing as people are looking for better ways to manage their energy.
The basic principle was this:
1. obtain a metal oil tank and cut it in half for the burn chamber
2. have a house nearby with hot water/baseboard heat (ours was about 20' away)
3. build a small 10x10x8' building out of concrete blocks around the burn chamber
4. add a door and smokestack to the burn chamber, with air inlet to control combustion
5. connect the water from the house baseboard to a copper coil (125'-200' iirc) and locate that above the burn chamber
6. fill in everything with sand
7. slap a roof on it
We heated our house from spare wood for years with that. Aside from the burn chamber melting, which was then replaced with 1/2" plate steel with railroad rail reinforcements, it ran pretty well for almost 15 years before we moved. Sadly, the new owners removed it.
If I were going to do something like this today, I would maybe combine it with a rocket mass heater in such a way to use less wood and be more efficient with the heat transfer and smoke output. I have considered doing something similar for heating a greenhouse, but smoke always gives me and my wife headaches so it isn't the right fit for us.
Roger
