Types of Electric Heaters for Your Home
A lot of homeowners consider that electric heating is the simplest way to warm spaces where a central heating system might not reach. Eventually, electricity is readily available, and many electric heaters can simply be plugged in—no hardwiring necessary. Electric heaters, which used when they truly needed, additionally can save users from turning up their main thermostat, a move that can translate into painful energy bills.
We’d like you to know about some types of electric heating, all with unique pros and cons.
The majority of Canadian households depend on a central furnace to provide heat. A furnace works by blowing heated air through ducts that deliver the warm air to rooms throughout the house via air registers or grills. This type of heating system is called a ducted warm-air or forced warm-air distribution system. It can be powered by electricity, natural gas, or fuel oil.
Inside a gas- or oil-fired furnace, the fuel is mixed with air and burned. The flames heat a metal heat exchanger where the heat is transferred to air. Air is pushed through the heat exchanger by the “air handler’s” furnace fan and then forced through the ductwork downstream of the heat exchanger. At the furnace, combustion products are vented out of the building through a flue pipe. Older “atmospheric” furnaces vented directly to the atmosphere, and wasted about 30% of the fuel energy just to keep the exhaust hot enough to safely rise through the chimney. Current minimum-efficiency furnaces reduce this waste substantially by using an “inducer” fan to pull the exhaust gases through the heat exchanger and induce draft in the chimney. “Condensing” furnaces are designed to reclaim much of this escaping heat by cooling exhaust gases well below 140°F, where water vapor in the exhaust condenses into water. This is the primary feature of a high-efficiency furnace (or boiler). These normally vent through a sidewall with a plastic pipe.
Heating system controls regulate when the different components of the heating system turn on and off. The most important control from your standpoint is the thermostat, which turns the system — or at least the distribution system — on and off to keep you comfortable. A typical forced air system will have a single thermostat. However, there are other internal controls in a heating system, such as “high limit” switches that are part of an invisible but critical set of safety controls.
Boilers are special-purpose water heaters. When furnaces carry heat in warm air, boiler systems distribute the heat in hot water, which gives up heat as it passes through radiators or other devices in rooms throughout the house. The cooler water then returns to the boiler to be reheated. Hot water systems are frequently called hydronic systems. Residential boilers usually use natural gas or heating oil for fuel.
In steam boilers, which are much less common in homes today, the water is boiled and steam carries heat through the house, condensing to water in the radiators as it cools. Oil and natural gas are commonly used.
A boiler uses a pump to circulate hot water through pipes to radiators, in lieu of a fan and duct system. Some hot water systems circulate water through plastic tubing in the floor, a system called radiant floor heating. Important boiler controls include thermostats, aquastats, and valves that regulate circulation and water temperature. Despite the fact that the cost is not insignificant, it is better to install “zone” thermostats and controls for individual rooms with a hydronic system than with forced air. Some controls are standard features in new boilers, while others can be added on to save energy.
As with furnaces, condensing gas-fired boilers are relatively common, and significantly more efficient than non-condensing boilers (unless very sophisticated controls are employed). Oil-fired condensing boilers are uncommon in Canada for several reasons related to lower latent heat potential, and potential for greater fouling with conventional fuel oil.
Heat pumps are just two-way air conditioners. An air conditioner works by moving heat from the relatively cool indoors to the relatively warm outside during the summer. In winter, the heat pump reverses this trick, scavenging heat from the cold outdoors with the help of an electrical system, and discharging that heat inside the house. Approximately all heat pumps use forced warm-air delivery systems to move heated air throughout the house.
Gas-Fired Space Heaters
In some areas, gas-fired direct heating equipment is popular. This includes wall-mounted, free-standing, and floor furnaces, all characterized by their lack of ductwork and relatively small heat output. Because they lack ducts, they are most useful for warming a single room. If heating several rooms is required, either the doors between rooms must be left open or another heating method is necessary. Better models use “sealed combustion air” systems, with pipes installed through the wall to both provide combustion air and carry off the combustion products. These units can provide acceptable performance, particularly for cabins and other buildings where large temperature differences between bedrooms and main rooms are acceptable. The models can be fired with natural gas or propane, and some burn kerosene.
Unvented Gas-Fired Heaters: A Bad Idea
Gas or kerosene space heaters that don’t have an exhaust vent have been sold for decades, but we strongly discourage their use for health and safety reasons. Known as “vent-free” gas heating appliances by manufacturers, they include wall-mounted and free-standing heaters as well as open-flame gas fireplaces with ceramic logs that are not actually connected to a chimney. Manufacturers claim that because the products’ combustion efficiency is very high, they are safe for building occupants. Meanwhile, this claim is only valid if you keep a nearby window open for adequate fresh air— which defeats the purpose of supplemental heat. Dangers include exposure to combustion by-products, as discussed in Ventilation, and oxygen depletion (these heaters must be equipped with oxygen depletion sensors).
Gas (and most wood) fireplaces are basically part of a room’s decor, providing a warm glow (and a way to dispose of secret documents), but typically not an effective heat source. With customary installations that rely on air drawn from the room into the fireplace for combustion and dilution, the fireplace will generally lose more heat than it provides, because so much warm air is drawn through the unit and must be replaced by cold outside air. Contrary to that, if the fireplace is provided with a tight-sealing glass door, a source of outside air, and a good chimney damper, it can provide useful heat.
State of the Art Heating
Radiant floor heat generally refers to systems that circulate warm water in tubes under the floor. This warms the floor, which in turn warms people using the room. It is highly controllable, considered efficient by its advocates, and is expensive to install. It also requires a very experienced system designer and installer, and limits carpet choices and other floor finishes: you don’t want to “blanket” your heat source.
Ductless, Mini-Split, Multi-Split. Residential ductwork is relatively rare outside 3Canada. “Ductless” heat pumps, which distribute energy through refrigerant lines instead of water or air, are widely used.
Combined heat and power (CHP) or cogeneration for houses is being seriously studied in some countries. The basic premise is to use a small generator to meet some of the electric demand of the house, and recover the waste heat (typically more than 70% of the heating value of the fuel) to heat the house (hydronic or water-to-air systems) and make domestic hot water. These systems are not yet widely available. They are likely to have the best economics in houses with high heating bills because the house cannot be feasibly insulated, such as solid stone or brick homes.