ASK THE EXPERT:
Is the old “rule of thumb” on watts needed to heat a room still relevant with new, tighter envelope homes?
Today’s new homes built to green standards may require much less heating. Most furnaces are typically way oversized for the space, and are geared to “worse case” low temperature needs. A homeowner desiring a heat pump or gas furnace can save money by sizing to average outdoor temperatures, and use supplemental heat for the main living areas during the limited days of sharp temperature drops.
With electric heat, Cadet has always advocated a general rule of thumb of approximately 10 watts per square foot for homes built prior to 1980 (R11 walls, R19 ceiling, single pane windows, 9 foot ceilings), and 6 watts per square foot for homes built after 1980 (R19 walls, R30 floor and ceilings, standard window thermal panes, 8 ft ceilings).
However, most new homes built after 2008 have tighter envelopes: R21 walls, R30 floors, and R38 ceilings are standard. Under this format, 4 watts per square foot will typically heat the room very comfortably; unless the room has greater than average window space or it is an extremely cold climate (add 2 watts per square foot). If you are still following the old rules of thumb, you may be adding more heat than is required.
What’s the harm in adding more watts than required? The heater will have more on/off cycles if it is oversized for the room. This reduces the life of the heater, may waste energy, and doesn’t maintain an even comfort level as well as a “right sized” heater.
Visit our online heat calculator at http://www.cadetco.com/heatloss.php if you have questions about sizing electric heat to newer home standards.