Choosing and Using Electric Heaters
Mar 12, 2001 (Updated Mar 30, 2001)
The Bottom Line Choosing and using the right type of electric heater can keep you both warm and safe.
Electric heaters can be an excellent and safe way to keep warm, and they can even help you save energy by allowing you to warm up the room you're in and turn down the heat in the rest of the house. Following a few tips will help you choose the most effective model for your intended use and also use it safely.
To begin with, all portable 120 volt electric heaters are limited by the Electrical Code to a maximum wattage of 1500. Almost all models available will offer from 1200 to 1500 watts of heating capacity, and the difference between 1200 and 1500 watts is not especially significant in terms of heating ability. All portable electric heaters heat through the principle of electric resistance, meaning that they create heat by using a heating element which gets warm when power flows through it. This means they are all 100 percent efficient; all models of the same wattage will produce the same total amount of heat and deliver the same 100 percent efficiency, producing 3,413 btu/hour of heat for every 1000 watts they consume.
HOW BIG AN AREA WILL THEY HEAT?
This depends on different factors, such as the insulation level of the room, the height of the ceiling, and whether the heater is the sole form of heat or just a supplemental heat source.
As a rough rule, with standard electric heating (anything but a heat pump) you need ten watts of heating power for every square foot of floor area. The maximum wattage you can get in a portable, 115 volt electric heater is 1500 (due to safety and code requirements), so this means that a portable electric heater can be the sole heat source for an area up to 150 square feet. As a supplemental heat source the area can be much larger.
If you want to use electric heating for a large area, you either have to use many portable heaters, each on a separate circuit, or install a 240 volt circuit and use a higher wattage model. For instance, on a 20 amp 240 volt circuit, up to 3840 watts of electric heating can be used.
HOW HEAT IS DELIVERED
While plug-in heaters are limited to 1500 watts, this does not mean that all heaters will produce the same heating results in any given situation. The key to effective heating lies in choosing the proper heating method for the area to be heated. The available options are fan-forced convection, natural convection, and radiant.
Fan-forced convection electric heaters use a small fan to force air past heating coils and out into the room. Heaters of this type can be very compact and inexpensive, with some models costing as little as $15. The advantage of a fan-forced heater is that it can warm an area relatively quickly since air is moved past the heating coils rather than being allowed to move throughout the room naturally. Some disadvantages are that heaters of this type can make a room feel drafty due to the moving air, and that the area nearest the heater is likely to be warmer than areas farther from it.
Safety-wise, fan-forced convection heaters are not quite as advantageous as natural convection models because a failure of the fan could allow the unit to overheat. Also, objects placed near the heater could block the airflow and likewise cause the unit to get too hot. Many good quality fan-forced models offer overheat sensors and tip-over switches to counter these disadvantages. Also, all-metal construction is a safety advantage since a metal heater that did overheat would not melt down or ignite the way a plastic one could.
Baseboard units and electric radiators are examples of natural convection heaters. These units take longer to heat up a room than fan-forced models, but once the room is warm, it will be uniformly so from wall to wall. Air moves past the warm surfaces of the heater by natural convection, with cool air being drawn in at the bottom of the heater and warmed before it is discharged back into the room.
Natural convection heaters are the best choice if you plan to use a heater often and want the safest possible option. Because they use no fan, there are no moving parts to fail, and the possibility of overheating is reduced. Electric radiators in particular are a safe and comfortable choice because the heating elements are completely inaccessible to the user, being immersed in a special type of oil. This oil also causes the heater to retain warmth even when the thermostat on the unit cycles the elements off, keeping the room at a very constant temperature.
With natural convection heaters, users just need to be careful not to block the airflow around the heater, especially above it, which is the primary direction the heat will move.
Radiant heaters are easy to identify by the fact that they have visible coils or quartz tubes that glow orange to red while they are in operation. Radiant heating is a different principle entirely from fan-forced or natural convection: Radiant heaters warm people and objects in a room. The air acquires warmth too, but only as it is given off by people and objects that have been warmed by the heater. Radiant heat is perfect for a workshop or other area that's usually unheated but where some heat is needed when a person is working there. Radiant heaters will make people near them feel comfortable far sooner than either type of convection heater.
As with fan-forced heaters, users need to be careful of how a radiant model is placed. Since objects in the path of the radiant heat can become very warm, it's crucial to keep a 3 foot space in front of the heater free of obstructions. A tip-over switch is a very good feature, too, since radiant heaters without that feature could pose a fire hazard if knocked over by a pet or a child.
General Safety Tips
While electric heaters can and do start fires, the vast majority of these are totally preventable if the user of the heater had followed basic safety precautions:
Don't overload circuits or outlets. Never use a small lamp-type extension cord for a heater, as the heater's high wattage (1200 to 1500) far exceeds these cords' rated capacity. It's best not to plug a heater into an extension cord at all, but if you have to, use a minimum of a 14 gauge (AWG 14) extension cord rated for more than the heater's wattage.
Make sure the outlet into which the heater is plugged is in good shape. If the heater's plug is held loosely in the outlet and tends to fall out, the outlet is worn out and should not be used to power the heater. Plug it in somewhere else or have the receptacle replaced, because a loose fitting plug will tend to get hot due to the fact that it's not making good contact inside the receptacle.
A heater poses an especially hard load on your home's wiring because 1200 to 1500 watts is a lot of power to draw through a circuit which may already have other things plugged into it. If you have an older home, consider a heater of 1200 or 1300 watts rather than the maximum allowable 1500, since that leaves a little extra capacity for other things that might be plugged in. Alternatively, consider a multiple wattage model that can be set to run on 750 or 1000 watts rather than 1500.
Use natural convection heaters, especially radiators, where possible. These are the safest type of electric heater because while their surface does get quite warm, it is not hot enough to burn people, and also is probably not hot enough to start most household materials on fire. They do not depend on a fan to keep the elements cool, so there is very little chance of a unit malfunctioning and overheating.
Be extra careful using heaters in bedrooms. Covers or blankets inadvertantly tossed off the bed during the night can cover a heater and start a fire. It's best by far not to operate any type of electric heater unless someone is awake to keep an eye on it, but if you have no choice, use a radiator or baseboard unit and place it where there is good airflow around it and no chance of anything falling onto or into it.
Shopping for the right type of heater and using it carefully can ensure that you not only stay warm on those cold nights but also that you and your family stays safe.