The answer to 'what is furnace' is a central heating system that uses natural gas, propane, or electricity to warm air and distribute it throughout a home or building. A furnace consists of a heat exchanger, blower, and ductwork that circulates the heated air through vents and registers. Furnaces are a common and efficient way to heat homes, especially in colder climates.
Furnaces are usually located in a basement, attic, or closet, and are designed to provide whole-home heating. They work by drawing in cold air, heating it, and then pushing the warm air through the ductwork and out into the living spaces. Most modern furnaces are highly energy-efficient, with features like variable-speed blowers and multi-stage heating that can adjust the output to match the home's heating needs.