The tarm solo 30 has been in operation about 3 weeks. Initially the oil backup was hooked to a two stage thermostat that was firing the oil burner when heat calls were over 1 degree. Experts on the forum suggested a different thermostat with an adjustable differential (Thank You). After much deliberation I decided to mount an aqua-stat on the storage tank that is currently set to fire the boiler on calls for heat when the tank water is below 120 degrees. The oil boiler does not heat the storage tank, only the heat zone for the house. I will let you know how this works out, I think it will work pretty well if we are away for a few days. Testing it today with no fire in the Tarm to see how close it will match the setting on the aqua-stat compared to the tank temperature thermometer. Again thanks to all the good people and information on this forum and Happy Holidays.