Residential Radiator Sizing

When installing a radiator, take under account the size and location of this room in addition to specific features, like the windows. These variables help determine how much heat a radiator must produce to keep the room comfortable. Heat output is measured in British Thermal Units, or BTUs. A BTU is the amount of heat required to raise the temperature of a pound of water by one degree Fahrenheit. Although commonly used in the heat and air conditioning business, BTUs do not mean much elsewhere, making it necessary to convert BTU dimensions into wattages when radiator shopping.

Doing the Math

First figure out the cubic footage of this space by multiplying the width, length and height of this space. Multiply the cubic footage from 5 when the radiator will be in a living room or dining room, 4 if in a bedroom and 3 to get a kitchen. Insert 15 percent to that amount if the space faces north and 20 percent when it contains a set of French doors. Deduct 10 percent when the windows in the space are double glazed. The amount you arrive in signals how many BTUs must heat the space. To convert BTUs into a measure of wattage, then split them by 3.41 since one watt of electricity will produce 3.41 BTUs in one hour.