Room Calculations for Electrical Heaters

Sizing the Heater

• The first piece of information needed is the overall square footage of the room. This is obtained by taking the length of the room and multiplying it by the width. The next step is to check the size of the heater. Most space heaters sold for home use are rated at 1,500 watts, and have a conversion ratio of 10 to 1, meaning that it takes 10 watts to heat 1 square foot of space. This means that a 1,500-watt heater is capable of heating a 150-square foot room. A larger room will require more space heaters in order to completely heat it.

Considerations

• Various factors will affect how well a space heater is actually able to heat a room. A room that is poorly insulated or drafty may require more wattage than a well-insulated room that has no drafts. The type of heater also makes a difference to the user. A radiant heater will warm people and objects directly in line with the front of the unit, but will not do much to warm the room as a whole. Convection heaters use fans to circulate the heated air throughout the room. These take longer to warm an area but are appropriate when the room is in continuous use and when the occupants will not be located directly in front of the heater.

Power

• It is important to be sure that the electrical heater being used does not exceed the capabilities of the outlet it is plugged into. The average American homeowner has 120-volt power throughout the house, with some appliances, such as an electric dryer or stove, plugged into 240-volt circuits. In most cases, a portable electric heater will be plugged into a standard 120-volt wall outlet that is rated at 15 amps. It is important that the heater does not exceed 80 percent of the 15-amp limit, as this will result in blown fuses or a fire hazard.

Safety

• Improperly used space heaters can be a serious fire hazard. A shut-off switch is an essential safety feature. This switch will shut off the heater if it is tipped over, preventing it from catching anything on fire. Extension cords can overheat if used for space heaters, and should be avoided if at all possible. If an extension cord must be used, it should be rated to carry the amount of current the heater requires, and the cord should never be placed under rugs or across walkways.