The US Department of Energy (D.O.E.) recognizes several different classes of residential heating equipment, including:
- central warm-air furnaces
- steam or hot-water systems (generally called “boilers”)
- heat pumps (both air-source and geothermal)
- floor, wall, or pipeless furnaces
- built-in electric units
- heating stoves (which burn wood, coal or pellets)
- room heaters (which burns gas, oil or kerosene)
- portable heaters
FurnaceCompare.com has comprehensive data on warm-air furnaces and boilers. Several of the D.O.E.’s definitions are included below for your convenience.
Central Warm-Air Furnace: A type of space-heating equipment in which a central combustor or resistance unit–generally using gas, fuel oil, or electricity–provides warm air that circulates through ducts leading to the various rooms. Heat pumps are not included in this category. A forced-air furnace is one in which a fan is used to force the air through the ducts. In a gravity furnace, air is circulated by gravity, relying on the natural flow of warm air up and cold air down; the warm air rises through ducts and the cold air falls through ducts that return it to the furnace to be reheated, thus completing the circulation cycle.
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Steam or Hot-Water System: Either of two types of a central space-heating system that supplies steam or hot water to radiators, convectors, or pipes. The more common type supplies either steam or hot water to conventional radiators, baseboard radiators, convectors, heating pipes embedded in the walls or ceilings, or heating coils or equipment that are part of a combined heating/ventilating or heating/air-conditioning system. The other type supplies radiant heat through pipes that carry hot water and are inlaid in a concrete slab floor.
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Heat Pump (Reverse-Cycle System): A year-round heating and air-conditioning system in which refrigeration equipment supplies both heating and cooling through ducts leading to individual rooms. A heat pump generally consists of a compressor, both indoor and outdoor coils, and a thermostat.
Floor, Wall, or Pipeless Furnace: Space-heating equipment consisting of a ductless combustor or resistance unit, having an enclosed chamber where fuel is burned or where electrical-resistance heat is generated to warm the rooms of a building. A floor furnace is located below the floor and delivers heated air to the room immediately above or (if under a partition) to the room on each side. A wall furnace is installed in a partition or in an outside wall and delivers heated air to the rooms on one or both sides of the wall. A pipeless furnace is installed in a basement and delivers heated air through a large register in the floor of the room or hallway immediately above.
Wood and Pellet Stoves: heating stoves can burn logs, wood pellets and other biofuels (such as corn). They can be configured as stove inserts (which fit into an existing fireplace and vent up a chimney — often retrofitted with a liner), or as stand-alone units, which vent out of specially installed stainless steel flue.