How Long Should A Central AC Run At A Time?

While having cool air circulate the room consistently can be comforting, sometimes we might consider cycling the AC. However, if you're not familiar with running ACs in a cycle, you won't know how long it should run at a time. It can be disastrous and annoying because it might mean exposing ourselves to fluctuating temperatures. So, how long should a central AC run at a time? If that's what you're trying to find out, let's take a look!

Ideally, your central AC should run 15-20 minutes at a time. However, several factors might increase that runtime. So, if you've found yourself surprised at the answer, there might be a few things going on. The following could be impacting your AC runtime:

  • Temperature outside
  • The size of your AC
  • Insulation quality
  • The thermostat setting

Now you might be curious as to what we mean by the list above. Some of the reasons might seem obvious, while others might need further explanation. In addition, you might want to find out what it means for your electricity bill. So, if you'd like to take a deeper dive into AC cycles, keep reading ahead to find out more.

Four air conditioning units outside of an upscale apartment complex, How Long Should A Central AC Run At A Time?

Factors That Could Impact Your AC Runtime

Temperature Outside

Let's start with the temperature outside. This reason might be one of the more obvious ones. The hotter the temperatures are, the more runtime your AC will need to cool the rooms in your home. 

Depending on where you live, the runtime of an AC can last longer than the ideal 15-20 minute cycles. For example, if you're living in Nevada, it's not uncommon to see temperatures going up to triple digits (100 degrees Fahrenheit or higher). So, if you live in one of the states where high temperatures are a common occurrence, you don't need to be alarmed about long cycles. 

Size of the AC

Central air conditioner

The size of the AC is something some users might not consider when purchasing a unit to install in your home. Though, it's one of the most important aspects of a cool room. The size of it can also be a factor in why you might have varying runtime differences. 

To clarify, it might be the case that your central AC is too small or too big for the room. You'll be able to spot which applies to you depending on a few signs. Let's go over them.


If you have an AC that's too big, you'll likely notice shorter bursts of runtime. Meaning, it will cool the room you're in within 10 minutes or shorter. While that might sound like a good idea, it isn't. Your AC needs time to regulate temperature and remove humidity. 

So, if it's cooling the room too fast, you might still feel hot and sticky. Additionally, it won't turn out well for your AC in the long run. It can cause damage to the compressor. And, an AC that has short cycles constantly means your AC will run up your electricity bill.


Now, we look at the opposite side of things. An undersized AC will have a longer runtime. In some cases, it might be running the whole time! The reason being that it isn't capable of reaching the temperature you set on the thermostat. 

The consequences of having the AC run for so long will show up in your electricity bill. Still, you should proceed with caution if your AC has lengthy cycles. As mentioned above, your AC might be running longer if the temperatures outside are hotter than average. 

The way you'll know the AC is undersized is if you don't notice a temperature difference during the whole AC cycle. However, this can also be an indicator of other problems such as dirty filters and low refrigerant. 

Insulation Quality

Insulation is what helps keep warm or cold air inside your home. Without adequate insulation, the efforts from your AC will go to waste quickly. Since the air is allowed to escape, your AC will try to compensate by running longer. So, your AC might short cycle or run longer to keep the temperature consistent.  

Thermostat Settings

Thermostat is set on an energy-efficient setting of 68 Degrees

This reason will depend on the person. Some people like temperatures that might be too low for others. So, they will reflect that on the thermostat setting. In combination with the weather, your AC will require a longer runtime to reach that target. 

So, if you notice your AC running longer than standard, take a look at the thermostat to see if anyone has lowered it by a couple of degrees. Increase the settings and observe if it makes any difference in the runtime.  

Is It Bad for AC To Run Constantly?

To determine if it's bad for the AC to run constantly, we need to clarify the situation you might be facing. If you're referring to short cycling, having the AC stop and start again consistently over time can result in damage to the system. 

More specifically, it can cause permanent damage to the compressor. Once the compressor stops working, the AC won't work as efficiently or at all. As some suggest, the AC will run continuously without making any significant changes to the temperature. Consequently, you'll notice the difference only in your electricity bill. 

Still, you might wonder why that might be the case. It happens because the AC needs a lot of power when it starts initially. If it's short cycling, it will be exposed to a large amount that it might not be able to handle. In other words, it produces an environment for more wear and tear on the internal parts of your AC. 

What Happens if AC Runs All Day?

If short cycling is not the situation you were referring to, then an AC that runs all day might be the cause for concern. In this case, the answer will depend on the situation. More specifically, is it out of character for your AC to do this?

To get more detailed, if your AC goes from running in cycles of 15-20 minutes to a sudden change of all day, it might raise concerns. Still, some units might be able to handle running all day. It can be a design in the AC you have installed.

But, you still need to check what could be causing it. Are the temperatures extreme in your area? This situation could cause your central AC to run all day. It will try to compensate by running for the whole day to keep it in your comfort range. In this case, having it run all day won't do any damage to your AC.

Should the AC Fan Be on Auto or On?

Exhaust fan of an air conditioner

Setting the AC fan on auto or on will depend on what you want to get out of it. There are pros and cons to both situations. So, let's take a look and see what fits your needs the best. 


Leaving the AC fan on "auto" is the more energy-efficient choice. It will only run once it detects a temperature difference that's not in your comfort zone. It allows for fewer filter changes. 

However, since the AC is not running all the time, you might witness uneven air distribution. Additionally, the air quality might not be as ideal as you want it to be. This can be a concern for people with allergies. 


The "on" setting indicates your fans will be running all the time. So, it will filter the air and distribute temperature more evenly. The disadvantage to running the fans all day is that it will cost more. And, like many other devices, it will decrease the lifespan because of frequent usage. 

An In-between?

If you're not happy with setting your AC fan on "auto" and don't want to increase your power bills substantially by leaving it "on," there are options you can consider. You can install a variable-speed blower. This way, you leave the fan running at a slower speed as a compromise. 

Can You Leave the AC Fan on All Night?

It is possible to run the AC fan all night if that's what you want. As some forum users suggest, it's safe to do but could be an expensive choice to make. However, it might not be as expensive as others make it sound if your AC fan can run at lower speeds. This situation will not apply to those with only a single-speed system. 

Regardless, if you want better air circulation for the night, it could be a worthwhile consideration. 

Is It Cheaper To Leave the Air Conditioner on All Day?

Leaving the AC on all day could be a cheaper alternative in certain situations. In one such condition, your area might be facing extreme temperatures. So, to compensate, your air conditioner will cycle longer to reach the target settings. In this case, it can be cheaper to leave the AC on to combat the weather. 

This way, you leave less room for humidity and heat to settle. Still, if you're not sure if it's something you should do, consult with a professional to see if your system can handle it. 

Final Takeaway

Making sure your AC runs well should be one of the top priorities to ensure your summers go along smoothly. While it might be worrying that your AC is running longer than usual, there might be an explanation for it to soothe your worries. We hope you found the information above helpful! 

Before you go, do you have other air conditioning concerns? Is the garage an area you're planning on air conditioning? We go in-depth with the topic in our post here.

Would you rather have a window AC running all night instead of the central AC? You can check if it's a safe and cost-effective alternative in our post here. Until next time!

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