In days of old, homes were poorly heated. Most rooms were cold because they had no heaters at all, so people gathered in the kitchen where the cook stove made the room the warmest in the house (the presence of food probably also attracted them). Or they gathered around the fireplace. The arrival of central heating systems greatly improved comfort throughout the home.
A central heating system has three parts: 1) a device that creates heat (furnace, boiler, or heat pump), 2) a means of moving the heat from the source to all the rooms in the house and 3) something to control the whole system. For us the heat maker is usually a furnace, a boiler or a heat pump. The heat mover we call a distribution system, which is usually comprised of ducts through which warm air moves or pipes through which hot water moves. We call the controller a thermostat, and it is usually located in the living room or in a hallway near the living room.
Furnaces and boilers
Furnaces and boilers use fuel to make heat. Furnaces heat air that is then moved to the living space through a network of ducts. Boilers heat water, which is then pumped through a network of pipes to the living space. Natural gas, oil and electricity are the most common fuels used in furnaces and boilers. We call furnaces and boilers that burn natural gas or oil combustion devices. They cannot be 100% efficient in making usable heat. This is because it is very difficult to completely burn any fuel and because some of the heat produced must be used to move the waste products of combustion up the chimney and outside the home. Combustion devices differ in efficiency from unit to unit. New units today range from about 80% to 95% efficient in putting the heat potential of their fuel into the distribution system. Older units can have efficiencies as low as 50%.
Electric furnaces and boilers do not burn fuel. Instead they convert electrical energy to heat energy and are 100% efficient.
Virtually all heat pumps run on electricity and are much more efficient in heating a home than an electric furnace. In fact, they can have an efficiency of 200% or more. Here's how.
Heat naturally flows from warm places to cooler places. That's the Second Law of Thermodynamics. But even wintertime air outside contains some heat. A heat pump moves that heat into the home. It's sort of like pumping water up hill. If your home has a heat pump the amount of heat it puts into the distribution system includes both the heat it pumps from outside your house to inside and the heat contained in the electricity used to run the heat pump. In the summer, heat pumps can reverse the process, moving heat from inside to outside.
There are two basic types of heat pump which are defined by the source of the heat they pump. The most common type is called an air source heat pump because it draws heat from the outside air. The other type is called a ground source or geothermal heat pump because it draws heat from an underground source, such as a well. Underground water usually stays at a temperature of about 55 degrees, so it contains more heat than wintertime outside air. Ground source heat pumps are generally more expensive to install because they require drilling a well (or laying pipe in the ground).
Currently, the minimum Federal Energy Efficiency Standard for heat pumps requires them to provide about twice as much heat as the potential contained in the electricity they consume. Therefore, heat pumps cost much less than electric furnaces to operate. How they compare with oil or natural gas furnaces depends on the current price for each of the fuels.
If you are interested in finding out if a heat pump is right for your home, take a look at our publication entitled: Purchasing a Heat Pump.
For more information from Seattle City Light on home heating, please
SCLEnergyAdvisor@seattle.gov or call 206.684.3800.
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