I am running through schemes to heat a 24x60' hoop house with wood. Currently it is heated with an LPG unit heater and consumes around 2000 gallons annually. The current useage is only March through the end of the heating season, and our farm manager would like to expand that to year round use. The easiest scheme I can see is to use the existing LPG tank (1000 gallons) as a heat source by moving it inside the greenhouse and heating the water with a wood boiler. How can I calculate the heat output of a bare tank at various temperatures? We could partially bury the tank in the ground if the heat output is too great. Obviously such a scheme would require maintenance fires to prevent the system from freezing up since that amount of glycol is not possible. Alternatively, we could buy a hydronic unit heater and run a glycol system. I see some advantages to the propane tank: first, it is free and a unit heater is not. Second, we could build frames over the tank and rotate seedlings through that hot zone.