Saving Energy With Electric Resistance Heating
Summary: This section will provide you with information on how to reduce your home's heating costs if you have an electric heating system. It doesn't cover heat pump technologies. Electricity is a versatile but precious energy source. Because it is needed for refined power equipment such as computers and medical machinery, when it is used for less-refined needs such as heating it should be used as efficiently as possible.
Electric Resistance Heat: Electric resistance heating converts nearly 100% of the energy in the electricity to heat. However, most electricity is produced from oil, gas, or coal generators that convert only about 30% of the fuel's energy into electricity. Because of electricity's generation and transmission losses, electric heat is often more expensive than heat produced in the home with combustion appliances, such as natural gas, propane, and oil furnaces.
Electric resistance heat can be supplied by centralized forced-air furnaces or by zonal heaters in each room, both of which can be composed of a variety of heater types. Zonal heaters distribute electric resistance heat more efficiently than electric furnaces because you set room temperatures according to occupancy. In addition, zonal heaters have no ducts that can lose heat before it reaches the room. However, electric furnaces can accommodate central cooling easier than zonal electric heating, because the air-conditioner can share the furnace's ducts.
Electric resistance heat can be provided by electric baseboard heaters, electric wall heaters, electric radiant heat, electric space heaters, electric furnaces, or electric thermal storage systems.
Electric Baseboard Heaters: Electric baseboard heaters are zonal heaters controlled by thermostats located within each room. Baseboard heaters contain electric heating elements encased in metal pipes. The pipes, surrounded by aluminum fins to aid heat transfer, run the length of the baseboard heater's housing, or cabinet. As air within the heater is warmed, it rises into the room, and cooler air is drawn into the bottom of the heater. Some heat is also radiated from the pipe, fins, and housing.
Baseboard heaters are usually installed underneath windows. There, the heater's rising warm air counteracts falling cool air from the cold window glass. Baseboard heaters are seldom located on interior walls because standard heating practice is to supply heat at the home's perimeter where the greatest heat loss occurs.
Baseboard heaters should sit at least three-quarters of an inch (1.9 centimeters) above the floor or carpet. This is to allow the cooler air on the floor to flow under and through the radiator fins so it can be heated. The heater should also fit tightly to the wall to prevent the warm air from convecting behind it and streaking the wall with dust particles.
The quality of baseboard heaters varies considerably. Cheaper models can be noisy and often give poor temperature control. Look for labels from Underwriter's Laboratories (UL) and the National Electrical Manufacturer's Association (NEMA). Compare warranties of the different models you are considering.
Electric Wall Heaters: Electric wall heaters consist of an electric element with a reflector behind it to reflect heat into the room and usually a fan to move air through the heater. They are usually installed on interior walls because installing them in an exterior wall makes that wall difficult to insulate.
Electric Radiant Heat: Electric furnaces and baseboard heaters circulate heat by moving air. In contrast, radiant heating systems radiate heat to the room's objects, including its people. For example, you can feel a ceiling-mounted radiant heating panel warming your head and shoulders if you stand underneath it.
There are several types of electric radiant heaters. The most common are electric heating cables imbedded in floors or ceilings. Other radiant heating systems use special gypsum ceiling panels equipped with factory-imbedded heating cables. Newer ceiling-mounted radiant panels made of metal provide radiant heat faster than other types because they contain less material to warm up.
Radiant heat offers draft-free heating that is easily zoned. Unlike other heating systems, it occupies no interior space. This allows you complete freedom to place furniture without worrying about impeding air flow from floor registers or baseboard heaters. Manufacturers claim that radiant heat can provide comfort similar to other systems at lower indoor air temperatures, saving around 5% of space heating costs.
Critics of radiant heat say that it can be difficult to control air temperature with a thermostat. The large heat-storage capacity of the concrete or plaster surrounding the heating cables may result in greater-than-normal fluctuations in the room air temperature, since it takes quite a while to heat up the storage mass. Also, some occupants complain about their heads being too warm in rooms that utilize ceiling radiant heat.
Supplying heat at the ceiling or floor, which are locations that typically border the outdoors or unheated spaces, can result in greater heat losses. For example, if there are any flaws in a heated concrete slab or gaps in the ceiling insulation above heating elements, a significant percent of the electric heat may escape to the outdoors without ever heating the home.
Electric Space Heaters: Electric space heaters come in a wide variety of models, either built-in or portable. These heaters may have fans to circulate heated air and may also be designed to transfer some of their heat by radiation. All of these heaters must be given adequate clearance to allow air to circulate safely.
Portable space heaters, as well as many built-in space heaters for small rooms, have built-in thermostats. Larger rooms heated with built-in electric space heaters should have low-voltage thermostats installed in an area that maintains the room's average temperature (see Thermostats for Electric Heating).
Portable electric space heaters can pose a significant safety hazard unless they have safety features and are used properly. Many cheaper or older portable electric space heaters are not safe for most home uses. Their red-hot elements and lack of safety features can lead to fires. When buying a portable electric space heater, select one with all of these safety features:
Tip-over switch that automatically shuts off the heater if it falls over,
Protective grille to prevent anyone from touching the heating elements, and
Sealed heating elements encased in metal or ceramic.
To use your portable electric space heater safely, follow these guidelines:
Check what other appliances share the space heater's electric circuit to prevent overloading circuits.
Avoid using extension cords.
Inspect the cord on the heater for any cracks or worn spots, and replace the cord or heater if any are found.
Make sure the area in which you are using the heater has a properly functioning smoke detector.
Keep combustible objects, such as blankets, furniture, drapes, toys, etc., at least six feet (two meters) away from the heating elements.
Electric Furnaces: Electric furnaces can be a more expensive long-term heating option because of their duct heat losses. The home's air is delivered to the furnace through return ducts, and heated air is delivered back to the home through supply ducts. If these ducts run through unheated areas, they lose some of their heat through air leakage as well as heat radiation and convection from the duct's surface.
Blowers (large fans) in electric furnaces move air over a group of three to seven electric resistance coils, called elements, which are each rated at five kilowatts. The furnace's heating elements activate in stages to avoid overloading the home's electrical system. Overheating is prevented by a built-in thermostat called a limit controller. This limit controller may shut the furnace off if the blower fails or if a dirty filter is blocking air flow.
Electric Thermal Storage: Some electric utilities structure their rates in a way similar to telephone companies and charge more for electricity during the day and less at night. They do this in an attempt to reduce their "peak" demand.
If you are a customer of such a utility, you may be able to benefit from a heating system that stores electric heat during nighttime hours when rates are lower. This is called an electric thermal storage heater, and while it does not save energy, it can save you money because you can take advantage of these lower rates. However, electric thermal storage is a seldom-used type of electric heating.
The most common type of electric thermal storage heater is a resistance heater with elements encased in heat-storing ceramic. Central furnaces incorporating ceramic block are also available, although they are not as common as room heaters. Storing electrically heated hot water in an insulated storage tank is another thermal storage option.
Some storage systems attempt to use the ground underneath homes for thermal storage of heat from electric resistance cables. However, this requires painstaking installation of insulation underneath concrete slabs and all around the heating elements to minimize major heat losses to the earth. Ground storage also makes it difficult for thermostats to control indoor temperatures.
Energy-Saving Measures: No matter what electric heating system you use, there are steps you can take to reduce your energy consumption. These methods include maximizing insulation, perhaps installing quality windows, reducing air leakage, using zone heating, and regularly replacing or cleaning filters in forced-air systems, all of which will make your home more comfortable and efficient and will save you money.
Insulation: To keep heating costs reasonable, electrically heated homes should be very well-insulated. Insulation's ability to slow heat flow is measured by R-value ( "R " stands for thermal "resistance"). The higher the R-value, the better the insulation restricts heat flow.
However, just because you have an adequate R-value does not necessarily mean your home is well-insulated. The insulation must be properly installed as well. Gaps and voids in the insulation-even small ones-create air convection or air leakage that markedly reduce rated R-values. See section Insulation.
Windows: Instead of R-value, windows are usually rated by their heat transfer coefficient, or U-value. The lower the U-value, the better the window's thermal resistance, or resistance to heat loss. While energy efficient windows are important in any house, electrically heated homes especially should have windows with U-values of less than 0.40. Advanced window designs incorporate multiple glazing layers, heat-reflective coatings, or gas fillings to reach U-values less than 0.25. Installing storm windows-even over double-pane windows-is often cost effective for homes in cold climates with high electricity costs. See section Windows.