A heater is a catch-all term for any device that heats up interior air. Furnaces, whether oil- wood- or induction-burning are heaters, as are steam-generating boilers and electrical resistance heaters. Heat pumps use the same heat transference principles as air conditioning to act as heaters. In our southwest Florida area, where heating needs are limited, many of our air conditioning units—whether central air or window unit—also include heaters for those rare times every year when heat is needed. Air conditioning heaters typically use electrically heated coils inside the air handler to heat air that is then blown into the home.