Determining your electric heating needs is calculated by the room size. This includes the total living area of the room to be heated. Remember that if you are in a particularly cold area of the country, check with your local inspector or heating and cooling contractor for correct sizing for you area. Just because your electric baseboard heaters have thermostats, doesn't mean you can always turn it up high enough to keep up with the heating demands. Do you know what wattage heater you need?