Furnace

The heating component of a central HVAC system that generates heat by burning fuel (natural gas, propane, or oil) or using electricity. It contains a heat exchanger where combustion (or electric coils) warms the air, which is then blown through ducts to heat the home. In a split system, the furnace is the indoor unit that works with an outdoor air conditioner or heat pump. Furnaces are rated by their output (BTU/h) and efficiency (AFUE).