When do I use "Supl. Heat" setting on my Heat pump?
29 January 2005
A. No. Iím constantly amused at the myths and superstitions I hear about heat pumps and to some extent I blame the heat pump industry for not educating their customersóthe homeowners who have themóbetter. Heat pumps are and remain mysteries to so many and have among a large population a very poor reputation for heating. They are great air-conditioners. If sized properly and installed in a building that is well insulated with all the doors and windows tight and doing what they are designed to do then a heat pump should be both comfortable and economical to own and operate.
There are times when the weather outside is so cold that a heat pump canít keep up. Our recent weather, for example. The heating load of the house increases by losing heat through windows and around doors, out bath and dryer vents, up fireplace chimneys and other normal heat loss avenues while the available heat in the outside air drops and that combination causes the system not to be able to supply the heat demands. The designers of the systems know this and thatís why the supplemental, sometimes called auxiliary, heat is built into the works. The supplemental heat is nothing more than electric resistance heating coils built into the air-handleróthe thing in the basement, closet or attic that houses the fan, heat exchanger and filters connected to the ducts and pushes the air through the house. The coils are much like the elements that glow red in your toaster when you turn it on and most folks avoid using them for heat because they use a lot of electricity and cost much more to use than the heat pump itself. You know when the coils are heating because the thermostat will have a blue or green light that will glow telling you that the supplemental or auxiliary heat is on line.
If the controls sense that the heat in the room where the thermostat is located is more than a degree or two below the setting, they kick on the supplemental heat to allow and help the heat pump to catch upóif it can. The heat pump itself isnít being overworked. Itís just that the work itís doing under those conditions wonít do the job required and it needs help and thatís what the supplemental or auxiliary heat is for.
Now, the trouble that most homeowners get into is not being able to interpret the relative duration that the additional heat operates with respect to the health of the heat pumpís outside unit. And the manufacturers arenít much help either. Itís that interpretation that your friends may have been warning you about but may not fully understand themselves. If itís fifteen degrees above zero outside and the wind is blowing twenty knots at your front door and your supplemental heat light is on, I wouldnít question it. However, if itís fifty degrees outside, mild winds blowing and the green light is on and you havenít touched the thermostat in hours, if not days, then you may have a problem and I would begin investigating. To complicate things even more-- most, if not all, heat pump thermostats have an emergency heat setting with a red light. If you throw the switch over to that setting you completely take the outside heat pump unit off line and you will heat with the electric resistance coils only. You can heat the house that way all winter but you will pay for it with much higher than normal electric bills.
I would say that over half of the heat pump units I examine have not been serviced since they were installed, regardless of age. They may seem to be working but even things that seem to be working OK need periodic service, like automobiles. Heat pumps do double duty in providing both heat and cooling. The only maintenance the average homeowner can perform is limited to cleaning or changing filters-- that should be done four times a year at the minimum-- and ensuring the outside unit is free and clear of obstructions like debris, close bushes or trees and build-ups of snow and ice. If you havenít done any of the above recently, including professional servicing, do it now.