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VERIFY: Don't set thermostat more than 20 degrees below outside temperature, if you have this kind of unit

Heat pumps typically can't cool more than 20 degrees below the temperature outside. Traditional AC units can -- but you'll want to take other energy precautions.

GREENSBORO, N.C. — Whew, it's hot this week. Much of the country is in a typical July weather pattern, and our thermostats are sweating almost as much as we are. 


It's a perfect time to answer viewer Pamela's inquiry. She wrote to the VERIFY team, "A heating and cooling company told us that the AC can't cool more than 20 degrees below what it is outside...so we adjust the thermostat accordingly. We have a heat pump."

Is it true you shouldn't set your thermostat more than 20 degrees below the outside temperature?



Both the U.S. Department of Energy and Triad-based custom builder Tom Garcia, who specializes in high-performance and environmentally-friendly homes, conclude the answer is -- true, depending on your system.

"That is true in some instances (like) when a person has a heat pump system. Heat pumps are very efficient, and they're great for our area, because we don't have extreme highs and extreme lows. So, heat pumps are wonderful. The thing about heat pumps is when we get really cold, they lose efficiency. If we get really hot, they lose efficiency." Garcia said.

That's why, Garcia explained, "A 20-degree margin is about right, although some heat pumps are better than that. It depends on the quality of the heat pump."

If you don't have a heat pump, and have separate AC and furnace units, you don't have to follow the 20-degree rule. However, do adjust the thermostat before you leave house.

The Energy Department suggests setting it to as high as comfortably possible in the summer and bumping it up even higher, when you're not home. The smaller the difference between the indoor and outdoor temperatures, the lower your overall cooling bill will be. 

But, if constant adjusting is too much of a hassle, Garcia suggested using a programmable thermostat.

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"These little babies are sleek, and they're not expensive anymore. They used to be. You can set them when you leave to go to work. You drop the temperature in your home or raise it four to five degrees," he said.

After that, it's all remote-controlled. "And then, before you come back -- maybe an hour or half hour before you get home -- let the system start to cool, or warm it back up again for you. That can really save a lot of energy," he explained.

Credit: tab62 - stock.adobe.com
Male hand holding smart phone to operate heating or cooling of thermostat for home

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One more key point Garcia emphasized is the importance is maintenance. He said a heat pump needs routine, easy service. Change out the filter every 30-or-so days and wash the coils with a hose to keep the air flowing well.


Yes, if you have a heat pump, don't set your thermostat more than 20 degrees below the outside temperature. If you have a traditional, standalone AC unit, you can set it to your desired temperature -- just adjust the thermostat when you're not home to save energy.

Do you have a VERIFY inquiry? Submit a post, screen shot or selfie video of the claim to Meghann via:

E-mail: VERIFY@wfmy.com

Facebook: Meghann Mollerus News

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