Baseboard Heater Basics

Baseboard heaters are mounted at the bottom of walls and powered by electrical circuits via wiring, which is usually routed through wall cavities to the main service panel. The wiring may route through a wall-mounted thermostat, or the thermostats may be built into the heaters themselves. While portable baseboard heaters are available that can plug into standard wall outlets, these are recommended for temporary use only. For the most efficient heating, it’s best to install permanent baseboard heaters mounted to the wall.  Permanent heaters are available in both 120-volt and 240-volt models. Wherever possible, install 240-volt heaters, as these are more efficient in terms of energy use. When shopping for baseboard heaters, you may notice many different specifications, including the length of the baseboard heater along with its wattage, amperage, and voltage. For the sake of choosing heaters that are sufficient for the space you need to heat, the wattage rating is the most critical. In general, longer baseboard heaters will produce more wattage. Here is an example from one manufacturer: 

Calculating Heater Wattage: A Quick and Easy Method

A very simple method to determine how much electric baseboard heating wattage you need can be found by calculating the square footage of the room, then multiplying it by 10 watts to produce a baseline wattage requirement.  For example, if you are heating a 12-foot x 12-foot bedroom, the space includes 144 square feet. Multiplying this by 10 watts shows that the necessary heater wattage for the room is 1440. This base wattage calculation method presumes that the room uses modern construction methods with typical wall, ceiling, and floor insulation and that it has 8-foot ceilings. If the room differs from these specifications, it’s recommended that you make the following adjustments: 

Add 25 percent more wattage if the ceilings are 10 feet high rather than 8 feet.  Add 50 percent more wattage if the ceilings are 12 feet high rather than 8 feet. In an older home, multiply the square footage by 12.5 watts, not 10. In an ultra-insulated home, multiply the square footage of the room by 7.5 watts, not 10.

For the sake of our example, let’s assume that the room has normal specifications. With 144 square feet, the required wattage is 1440 watts, which means you could heat the room with a single 1500-watt baseboard heater or two 750-watt heaters.

Calculating by Length of Baseboard Heater

In this method, it’s assumed that 240-volt baseboard heaters typically produce about 250 watts per linear foot of length. This calculation is designed to tell you how long your baseboard heater should be. 

Each windowEach exterior doorEach exterior wallAn uninsulated space below the roomPoorly insulated wallsCeiling more than 8 feet tall

The resulting number will be the total wattage required for baseboard heaters to heat the room. Now, divide by 250 to arrive at the length of the baseboard heater required.  Using the same size room as described in the first calculation method, we’ll assume that our 144-square-ft. bedroom has one window and two exterior walls but is otherwise typical. The calculation runs like this: 

It is always best to slightly oversize when selecting baseboard heaters. There is no loss of efficiency by heating your space with baseboard heaters that are slightly larger than the minimum requirements. For example, a 30-amp circuit can accommodate a baseboard heater rated for 500 square feet or 4,500 watts, but the same heater will be more efficient at heating a smaller room (assuming the circuit size is appropriate). It’s also possible to put two or more baseboard heaters on the same electrical circuit as long as their total combined wattage is not higher than the circuit’s maximum capacity.