What Is a Furnace?

A furnace produces heat by burning fuel — natural gas or propane — and transfers it to indoor air through a heat exchanger, with combustion gases vented outside. It differs fundamentally from a heat pump, which moves existing heat rather than creating it by combustion.

Also called: gas furnace · propane furnace

Why it matters to you

In eastern North Carolina a furnace is more often the backup half of a dual-fuel system than the primary heat source, because the heat pump carries most of a mild winter. That changes the calculation on efficiency upgrades: a furnace running few hours a year accumulates less benefit from a higher AFUE.

What to do about it

Annual inspection matters on any combustion appliance, specifically the heat exchanger and the venting. Fit carbon monoxide alarms on every level of the house regardless of how new the equipment is.