I am building a Hybrid Electric/Compost heated hot tub. The plan involves a 55gallon drum (single person) surrounded buy leaf compost contained by 5 pallets. I have a timer and 1000W electric bucket heater. I also have a drain spout and valve. I will insulate the top with a thick piece of styrofoam. I hope to keep my pile active through the winter and enjoy the hot tub. Thoughts?
I was thinking about your idea and I think that its definitely plausible. I would recommend doing something similar to this.
basically just running some pex pipe through a compost pile. Then have it circulate into an old used hot tub or well insulated 55 gallon drum or heck even an old deep freezer. You might need some additional heating but it would likely be pretty minimal compared to no heating from compost. Hope this gives you some ideas.