There are several types of heating system technologies. Most heating systems work in one of three ways: they burn a fuel to create heat, they convert electricity directly into heat, or they move heat from outdoors into the home. Heating systems also differ in how they distribute heat throughout the home, which fuels they can use, and how much energy they require to operate.
Furnaces are the most common type of heating system in the United States. A furnace heats air and then uses a blower fan to distribute the warm air throughout the home through a network of ducts. This is often called a forced-air system.
Furnaces can be powered by natural gas, propane, fuel oil, or electricity. Fuel-burning furnaces create heat by burning fuel in a combustion chamber, while electric furnaces use electric resistance heating elements, similar to those in a toaster.
Because furnaces rely on ductwork to distribute warm air, the condition of the ducts can significantly affect system efficiency. Leaky or poorly insulated ducts can allow heated air to escape or lose heat before reaching the rooms they are intended to warm, especially when ducts pass through unheated attics, garages, or crawl spaces.
Boilers heat water rather than air. The hot water, or in some older systems steam, travels through pipes to radiators, baseboard units, or tubing installed beneath the floor. These surfaces then release heat into the room.
Heating systems that warm surfaces rather than blowing air are often called radiant heating systems. Many people find radiant heat especially comfortable because it warms floors and objects in the room and does not create drafts.
Boilers are commonly powered by natural gas, propane, or fuel oil, although electric boilers are also available.
Heat pumps work differently from furnaces and boilers. Instead of creating heat, they transfer heat from one place to another. During cold weather, a heat pump extracts heat from the outdoor air, ground, or water and moves it into the home. Even when it feels cold outside, outdoor air still contains heat that a heat pump can capture.
Because moving heat requires much less energy than creating it, heat pumps can deliver two to four times more heat energy than the electrical energy they consume. Heat pumps can also reverse this process in the summer to provide cooling, allowing one system to both heat and cool a home.
Heat pumps are often categorized by the medium they exchange heat with. Air-source heat pumps exchange heat with outdoor air. Ground-source heat pumps, also known as geothermal heat pumps, exchange heat with the ground. Water-source heat pumps exchange heat with water. Depending on the system, the water source or loop may be located above or below ground. Heat pumps can distribute heat through central ductwork, or they can use ductless mini-splits, which connect one outdoor unit to one or more indoor units mounted in individual rooms.
Older air-source heat pumps lost efficiency in very cold weather, but modern cold-climate heat pumps are designed to continue heating effectively at temperatures well below freezing. Most heat pumps also include backup electric resistance heating, often called auxiliary heat, that turns on when the heat pump alone cannot keep up with heating demand.
Heat pumps are powered exclusively by electricity.
Dual-fuel systems, sometimes called hybrid heating systems, pair an electric heat pump with a furnace that burns natural gas, propane, or fuel oil. The heat pump provides heating during most of the year, while the furnace takes over during the coldest weather.
Because the furnace still burns fossil fuels, dual-fuel systems continue to produce indoor combustion risks and greenhouse gas emissions whenever the furnace runs. Modern cold-climate heat pumps can now heat homes effectively in most US climates without a fossil fuel backup, making an all-electric heat pump system the cleaner long-term choice.
Electric resistance heaters convert electricity directly into heat by running electric current through a heating element. Common examples include electric baseboard heaters, wall-mounted heaters, and portable space heaters.
Electric resistance heaters are inexpensive to purchase and simple to install, and they can heat individual rooms without ductwork. However, they convert each unit of electricity into only one unit of heat, making them one of the most expensive ways to heat a home in most regions.
Wood stoves and pellet stoves burn wood or compressed wood pellets to heat a room or small area. They are most commonly used as a supplemental heat source alongside a home's main heating system.
Modern, certified wood and pellet stoves burn fuel much more cleanly and efficiently than older models. Open fireplaces, on the other hand, are generally inefficient heat sources. While they provide warmth directly in front of the fire, they draw large amounts of heated indoor air up the chimney, which can cause the home to lose more heat than the fireplace provides.
Wood-burning appliances also release smoke and fine particulate matter that can affect indoor and outdoor air quality, so proper installation, venting, and maintenance are important.