Bob's Tip of the Day: Furnaces heat air. If your heating appliance heats water, then it’s a boiler. If your appliance sources heat from the air, the ground, or a water reserve, then it’s one of several types of heat pumps. If there are ducts through which warm air blows, then you have forced-air distribution. If you have baseboard radiators, your distribution system is hydronic (hot water). If the heat comes from your floors (or walls or ceiling), you use radiant heat distribution.