What Size of Wall Heater Do I Need?

The heat output of wall heaters in measured in watts (W), a unit of power equal to 1 joule (J) per second. In order to determine what size wall heater you need, you should determine the square footage of the space to be heated, estimate the heat losses from the space and match the heat output of a wall heater accordingly.

Square Footage

The square footage of a space can be determined be measuring its length and width and multiplying the two figures together. A typical 14-foot by 12-foot room has a square footage of 168 square feet.

Energy Efficiency

Heat loss from a space is important because older spaces with little or no insulation and single, rather than double, glazed windows will lose heat more quickly than newer, energy efficient spaces. It stands to reason that if more heat is lost, a more powerful wall heater is required to maintain a comfortable temperature in the space.


As a general rule of thumb, 10 watts of heat output are required to heat each square foot of a properly insulated space. So, assuming that a 14-foot by 12-foot room is above average for energy efficiency, a wall heater with an output of 1,680 watts or 1.68 kilowatts (kW) would be adequate to heat it comfortably.

About the Author

A full-time writer since 2006, David Dunning is a professional freelancer specializing in creative non-fiction. His work has appeared in "Golf Monthly," "Celtic Heritage," "Best of British" and numerous other magazines, as well as in the book "Defining Moments in History." Dunning has a Master of Science in computer science from the University of Kent.