What Temperature to Leave a Vacant House in Summer?

average house temperature in summer

Summer 2024 might officially be over, but September can bring a wide variety of weather across the U.S, including late-season heat waves.

Whether you leave your house to go to work every morning or planning a late summer vacation, you might be wondering what temperature to leave your vacant house to avoid ranking up the energy bills.

Turning the AC Off Is a Bad Idea

One of the most commonly held beliefs is that turning the air conditioning off while you are gone will save electricity, but that’s not always correct. When it’s hot outside, returning to a home that’s been ‘baking’ on the sun all day won’t be pleasant and your AC unit will have to work a lot harder to cool it down again.

In addition, your HVAC system doesn’t only control the heat levels, but humidity levels as well. If you turn off the AC for a prolonged period of time, especially in a hot season, you can return to discover any of the following unpleasant problems:

  • Mold
  • Musty smells and odors
  • Peeling paint
  • Warped wood furniture (floors, cabinets, etc.)

That’s why energy experts advise that rather than turning your air conditioner off completely, you should just set back the thermostat temperature which can save as much as 10 percent on annual heating and cooling energy use.

So what’s the best thermostat setting for an empty house in the summer?

Thermostat Settings in Summer

During summer, it is generally recommended to set the thermostat to 78 degrees Fahrenheit when you are at home (and 68 degrees in the winter). When you are going away (whether for several hours or 1-2 weeks), consider raising the setting of your AC by 10 to 15 degrees, so that the cooling system doesn’t kick in until the temperature tops 88 degrees Fahrenheit or higher.

Use a Smart Thermostat

That being said, having to remember readjusting the thermostat every day before leaving for work is frustrating. If you are in a rush or forget, it can cause you extra stress and unnecessary energy costs. Luckily, thanks to technological progress, we can now train our machines to do the thinking for us.

What are we talking about? Smart thermostats of course.

smart thermostat is perhaps the most effective way you can manage temperatures in your home. You can set it to automatically adjust the air conditioning at preprogrammed times that coordinate with your schedule. By the time you return home, your air is cool again and you don’t have to deal with a hot, stuffy house.

Other Ways to Make a Vacant Home Energy Efficient

Don’t put all your eggs in one basket, meaning don’t rely only on your air conditioning to cool down your house. There are other, less costly tricks that you can implement to keep the heat out and fresh air in.

Close Blinds and Curtains

Sunlight beaming in through the windows can heat up the place really quick – according to the U.S. Department of Energy, 76% of the sunlight that falls on standard double-pane windows enters to become heat.

What to do? Close your curtains on your way out or even when you are at home. The DOE notes that medium-colored draperies with white-plastic backings reduce the heat gain by 33 percent.

Another option is insulated cellular shades, made of pleated material and designed to fold up in an accordion-like fashion. In heating seasons, tightly installed cellular shades can reduce heat loss through windows by 40% or more.

Turn Down the Water Heater

One often overlooked saving is turning down the water heater to the lowest setting when you are away. Just make sure to remember to turn it back up before you take that first shower when you return!

Unplug the Appliances

Even items (be it the TV, toaster, microwave, or a stereo) that are turned off with a button still consume electricity and when added up, cost you a few extra dollars on your utility bill. Make sure you unplug everything before you leave for your vacation! Even better, consider getting a smart power strip, which shuts off electronics that are no longer in use, to avoid high standby power costs.


Is 78 degrees too hot for a house?

Department of Energy recommends keeping your home at no more than 78 degrees when you’re home in the summer. When you’re at work or away for a week or two, adjust the thermostat up by 10 – 15 degrees, meaning that it won’t kick in until the heat reaches at least 85 degrees.

How long can I leave my house vacant?

Whether you have to leave your house to go to work every morning or you are going on a short trip, it might be more economical for your air conditioning to stay on at a higher degree, then being turned off completely. So what temperature for an air conditioner is ideal for an empty home? According to DOE, you should adjust the thermostat up by 10 – 15 degrees from your normal setting when you are at home. If you are going on a trip that is longer (more than a month), you are probably better off turning the AC off completely. However, the problem you are facing in that scenario is moist air entering the building and the potential development of mold.

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