Buildings

Thermostat Setback

by Arnie Katz

Q:  I have a heat pump to keep my house warm. I have been told that it is better to set the thermostat at one temperature and forget it verses turning it down at night and when I'm not going to be home for several hours. What is the most energy efficient?

A: This is a great question. The short answer is that in general, you're better off setting the thermostat for your heat pump as low as possible for you to be comfortable and just leave it there. Let me explain, since this doesn't seem logical.

The idea of setting back the thermostat is that you can save money by letting your house get cooler during the day when no one is home or at night when everyone is comfortably covered by grandma's quilts. Keeping the house cooler for extended periods will definitely use less energy.

If you have a heat pump, however, it gets a little more complicated. If you let the house cool down, then when you want to heat it back up, the heat pump by itself may not be able to bring the house up to where you want it in a reasonable amount of time. When this happens, the back-up heat strips come on to help out. Also called "emergency heat" or "auxiliary heat," this back up is essentially a toaster that installed in the air handler unit.

The toaster (electric resistance coils) puts out a lot of heat quickly and can make the house comfortable. Unfortunately, this uses a lot of electricity, so you will spend a bunch of extra money. You've saved energy, but since the toaster uses a lot more electricity than the heat pump by itself, it will wind up costing you more money.

If you are comfortable with high tech gizmos—or have a teenager in the house—it may be worth considering installing a programmable thermostat designed specifically for heat pumps. These are programmed to gradually step up the heat over a long period of time without using the heat strips, and can save you some money both in the winter and in the summer.

But make sure you have a knowledgeable technician install it and that you are comfortable setting the program and "playing" with it until you get it where it works for you and your family.

If you have a gas or oil furnace, setting the temperature down during the day or at night will save you money, whether you do it automatically with a programmable thermostat or manually. In general, a heat pump is the lowest cost heating system in North Carolina, even if you don't set it back.