What is the difference between a furnace and a boiler? The major difference is the medium used to distribute heat. Boilers use water or steam and furnaces use air. Furnaces can heat the air with any number of sources and the most common ones are electricity, gas and oil. There are two primary types of hot air systems; gravity systems which move the hot air naturally upward through ducts in the home and forced air systems that push the hot air using a fan.
Forced air systems allow for more flexibility than other systems by allowing integration of humidifiers, dual use of ductwork for cooling and a limited ability to control heat in individual rooms. Care is required when closing ductwork, as closing too many registers can damage system components.
Heat pumps are another option, see the Heat Pump section for details.
Conventional gas furnaces come in many sizes (measured in BTUH) and they can be installed or mounted in many locations if there is enough room for venting the products of combustion outside. The most common spots are the attic, crawlspace, basement or utility closet.
Boilers frequently use baseboard or radiator distribution systems. In these heating arrangements, hot water or steam is pumped throughout the home. As it enters the baseboard units or radiators, fins or ribs allow the heat to radiate into the room, warming the air. A less common method of distribution is through tubing in the floor.
Baseboard systems are not a flexible as forced air as it is difficult to turn off sections of radiators.
Baseboard electric is commonly used in locations with milder winters and lower electric rates. It can be the least expensive system to install, but a consideration should be taken with the cost of operation. The advantage of baseboard electric is the ability to use it in areas without ductwork or hot water/steam piping. Another advantage is the ability to control the heat in each room individually.