I have a 1400 sq. ft. apartment in central Maine in a renovated barn with radiant floor heating. The floors downstairs are concrete and upstairs wood. A Tarm gasification boiler with 820 gallon storage tank is used to heat the floors and DHW. This system was designed by professionals and the total heat load is 40kBTUs/hr. It is a passive solar design so when the sun shines it helps but it doesn't shine a lot in the winter. I have been very happy with the system but I would like to leave for a week or two and I'm looking for a back up system, any recommendations would be appreciated.