Methane is a by product of aerobic bacteria....micro -beasties...they generate the heat and break down the solids...Methane is explosive.
Compost piles stay outside...google
The genius of Jean Pain...Mother Earth news
Or the Jean Pain method..pdf
Or
The compost powered water heater by Gaelan Brown.... Hot water in house compost outside....pain also collected methane to run machines on his farm....
