British thermal units (BTUs) is the measure of heat. Residential grade oil (NO.2) provides 138,600 BTUs per gallon. Propane only provides 91,600 BTUs per gallon. Anotherwords, propane only provides 66% of the heating BTUs as NO.2 oil. The current price for No.2 oil in Maine, as of Dec 1, 2008, is about $2.70 per gallon, and current price for propane is in Maine is about $2.85 per gallon. Assuming that there are two furnaces, one that burns oil and one that burns propane, and they are both 83% efficient. If you burned NO.2 oil, it would cost you $23.47 for every million BTUs of output. If you burned propane, it would cost you $37.49 for every million BTUs of output. Fuel doesn't necessarily burn more efficiently, but one boiler or furnace can be more efficient than another, based on its construction and how it burns the fuel. Some gas furnaces, such as condensing types, are as nuch as 93% efficient. One good way to save fuel, whether you burn oil or propane, is to get the most efficient unit as possible.
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