In much of the United States, space heating is by far the largest energy user in the home, and the venerable forced air furnace is the most popular means to meet this need. Furnaces are present in nearly 50 million homes around the country. It’s no wonder that manufacturers and researchers have spent considerable effort improving the combustion efficiency of furnaces—so much so that some models can wring more than 95% of the energy from their input fuel.

But until recently, the push to develop and promote energy-efficient furnaces has largely ignored the fact that furnaces require a lot of electricity to operate. The furnace fan motor is often the largest motor in the home, and it can easily rack up more than 1,000 hours of operation per year in the course of distributing heat in the winter and cooling in the summer. Furnace electricity use is an especially significant expense in homes where the furnace fan is run continuously for air filtration and other reasons.

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