Comparing Fuel Costs

To further complicate matters, the amount of usable heat we get from a fuel also depends both on the efficiency of a given heating device and on how efficiently that heat is distributed to the conditioned space. The efficiency of combustion appliances varies widely, from a low of about 40% for older woodstoves to over 95% for condensing gas furnaces. Electric-resistance baseboard heaters are 100% efficient, while heat pumps, which use electricity to move heat from one place to another instead of converting the electricity directly into heat, range in efficiency from 200% to over 300%. (These numbers don’t account for the “upstream” energy costs of fuel production, nor do they begin to account for environmental costs—which are pretty significant with some forms of electricity generation.)

As for distribution efficiency, forced-air heating is often a lot worse than hydronic baseboard heating. If poorly sealed ducts are run through an unheated attic and insulated only to R-4, as is typical in the U.S., the heat-delivery efficiency will likely be only 60%–65%. Multiply that by a standard furnace efficiency of 78%, and you’re getting only about half of the heat you’ve paid for.