A.Martin Holladay responds: The short answer is that oil is almost always cheaper. Simply comparing the per-gallon prices of the two fuels does not provide a fair comparison, since a gallon of propane has a much lower thermal value (91,600 Btus per gallon) than oil (139,000 Btus per gallon). Remember that a fair comparison must take into account the heating efficiency (AFUE) of the furnaces or boilers being compared; these may be different, depending on the equipment you are considering. Finally, prices vary regionally. The following table shows how cheap propane must be in order to match the price of oil, assuming heating equipment of the same efficiency.

Martin Holladay is editor of Energy Design Update. For subscription information, call 800/638-8437.

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