I've moved to a "new" house - built about 350-400 years ago. Firewood in a stove kind of works for heating a few rooms, but not the full house. So far it seems like the grid power tends to die about twice a month. Temperatures is expected to reach -25C (-13F) for the coldest couple of weeks every winter. Hence I need some kind of backup power and heat source. The house is located in a small hill side, facing south-west. From about 15th of November some near by mountains is blocking the sun, so solar energy will be zero for at least 2 months/year. On the property trees grow faster than I'll ever be able to burn them, so there is unlimited access to firewood. Energy required to heat the house seems to be about 3kw at 0C outside. That should indicate the need for 7kw for the coldest days. I have an idea: What if I install water tubes in all floors and build a wood burning waterheater in a "stove house" somewhere down hill from the house. Could this be made in such way that water will circulate from thermosyphon effect, without any pump (needs to work even when grid power dies). A convenient place to put the stovehouse will be 16m from the house. Then the base of the stove will be 5,5m below the floorlevel. Could this be enough to make the thermosyphon work? Will it be able to transport 7kw of heat? (What is required in order to make such system work?) I'm thinking of making the stovehouse burn logs, maybe 2m long, maybe some kind of autofeed. Also I'm thinking of storing logs on top of the stovehouse to let the waste heat help to dry the logs. Hence the time consumed to deal with firewood should be minimized.