How Long You Can Leave Your Air Conditioner Running: Solved

An Air Conditioner blowing cold air

In these hot summer months, nothing could be better than that blast of cool air when you walk back in the door.

But the pleasant feeling can quickly be offset by an outsized electricity bill— or, worse, an air conditioner repair bill. Is it safe to leave the air conditioner running all day? And more importantly, is it expensive?

Because of the energy it takes to get started, an air conditioner can be more efficient when left on, even when we leave for errands. Only when you can leave it off for hours, like during the work day or at night, is it always a better choice to turn it off. Otherwise, just adjust the thermostat.

Keep reading for more efficient cooling!

When to Run Your Air Conditioner

Since we know we should use our air conditioner when it gets hot, the question we have to answer is when and how long should your air conditioner run?

First, we need to distinguish between active running and just being on.

Your air conditioner can be set to cool the house to 70 degrees all day, but if your house never gets higher than 68, it won’t spend very much time being active. Meanwhile, if your air conditioner is set to 70, but it can’t cool the house below 80, it will overstress itself chugging along endlessly.

The first thing to recognize is the limits of your air conditioner. Most air conditioners can cool a room or house by 20 degrees Fahrenheit (see our article on how cold to set your AC). On very hot days, this might mean setting your thermostat higher than you would like.

Of course, every degree difference in your AC setting can save up to 5% of the electricity it consumes, so you should already consider leaving it a little higher than you otherwise might. After all, there are plenty of other good ways to keep cool without relying on the AC.

How do you know if your air conditioner is working too hard? The general rule is that it should run for 15-20 minutes at a time.

If you don’t feel any change in that period, either your air conditioner is a poor fit for your home or there may be a problem with it. When you set the unit to cool down to a lower temperature, it might run longer, and that’s okay once in a while. However, if it regularly takes a half hour or more to make a difference, make sure it’s working properly and consider looking into buying a bigger one.

Surprisingly, the opposite issue also exists. It’s very possible to have an air conditioner that’s too big. An outsized unit will cool your house down, and it will do it very quickly. However, rather than running for twenty minutes every once in a while, this big unit will run less than ten minutes at a time, all the time.

Constantly turning on and off is a process known as short cycling. This doesn’t only lead to an unsteady temperature but also causes power spikes and inefficient electricity usage. In the long run, you’ll find yourself paying a lot more. Short cycling can also lead to humidity issues as the AC doesn’t run long enough to dehumidify the air properly.

Air Conditioner Hissing
An air conditioner running too long or too short of a cycle time may warrant a professional look.

The Costs of Running Your Air Conditioner

Although we all like easy answers, the truth is there are many factors that influence the cost of running your air conditioner. Some of these are obvious, such as the price of electricity or the outside temperature. Others are trickier to measure.

Whether your home is well-insulated, how large of an area you’re trying to cool, how the rooms are laid out (and whether doors are open)— and even where the thermometer is can affect how your air conditioner runs. See our window air conditioner running cost guide for all you need to know about what influences the cost, as well as some helpful calculators specific to window air conditioners.

There are a lot of online sources that tell us that running our AC all day every day can get expensive. Not only does it start to wear out the unit, but it can also drive up electricity bills. Some of these lists speak in the most dramatic terms, making us feel like running the air conditioner is the worst thing we can do. After reading that kind of article, we might want to just throw out the whole thing!

But the truth is summer is hot, and it’s important to our health that we have relief from the heat.

Honeywell Office Fan
It’s impossible to get work done in a hot room. When it comes to whether or not to run your air conditioner – you’re worth it!

Although running the air conditioner is more expensive than leaving the house sweltering, a hospital bill costs you all of those savings and then some: at $3000-$7000, a trip to the hospital costs so much that you could run a window unit for a century.

So while we might not want to run our AC on the first warm day of spring, there really is no other choice when the dog days of summer roll around again.

Should I Turn Off My Air Conditioner When I Go Out?

Coming home to an icy blast in the height of summer is the best part of the working day. But is it sensible to leave the AC on for eight hours or more while we’re out and about? In terms of simple energy consumption, it’s simply better to leave it off. However, that’s not the whole story.

There are a few variables to keep in mind:

  • How long you’re going out affects whether you should leave the AC on: Think about pushing a heavy shopping cart. It’s a lot of work to start moving it, but when it’s rolling already, it doesn’t take much to keep it going. It’s the same with air conditioning. It takes a lot more work, a lot more electricity, and a lot more wear and tear, to drop the temperature ten degrees than to keep the temperature ten degrees lower for the same amount of time. If you’re just stepping out for a few minutes, it can be better for your AC and your bills to just leave it running.
  • Don’t forget about your furry friends: Fido doesn’t have sweat glands, and even though animals have their own ways to keep cool, you shouldn’t let your house turn into a sauna if dogs, cats, or other pets are staying there all day. If you’re going out a long time, you can certainly turn the AC down, but make sure to keep it cool enough that the dog days of summer aren’t your dog’s worst days. You want your cool cats to stay that way! In general, pets don’t want it to be much hotter than 80 degrees Fahrenheit.
  • You can let the AC rest at night: Although the obvious time to turn down the AC, at least a little, is when you’re gone all day, nighttime is the best time to let the air conditioner rest. Not only is it cooler outside (maybe cool enough to crack the windows!), but when we sleep, we generate a lot less heat. Even under the blankets, we need less help keeping cool than when we’re hurrying about our day.
  • Experiment with a higher setpoint. If you’re heading out for the day, it’s often a great idea to leave the air conditioner on at a “higher setpoint”. All this means is leaving it running at a slightly higher temperature than normal, and adjusting it back down when you get home. This gives you the best of both worlds – it keeps the momentum going during the day, without ramping up your energy bills with a lot of wasted energy.


Although it’s never free to run the AC, it can be more efficient to keep it running more often than you’d think.

Take advantage of long hours out and of nighttime chill to let it rest, but don’t be afraid of your air conditioner. Especially on hot, busy days, we should all take the opportunity to chill out.

If this information helped you out, please consider taking a look at the related articles below.

Thanks for reading, and stay cool out there!

I've been helping homeowners with appliance repair since 2016. Starting out as an enthusiastic amateur, I've since worked with many Appliance, HVAC, and DIY experts over the last 7+ years. My mission is to help fix your appliances and prevent future issues - saving you stress, time, and money. Visit my author page to learn more! Read more