On hot summer days, you want your air conditioning to keep you cool—but you also want it to run as efficiently as possible, for both your wallet and the planet. 

When it comes to just how many hours a day your AC should be running, the answer really depends on the temperature outside. Of course, in order to really maximize efficiency, you’ll need to make sure it is the right size and type for your home. 

How Many Hours Should AC Run Per Day 

There is a general answer to the question of how many hours per day your AC should run: Between 12 and 16 hours on an average summer day. However, the actual number will depend on some specific factors, including the ones below:

  • The temperature outside
  • The temperature you are trying to achieve inside 
  • The size of your air conditioner 
  • The type of unit you have 
  • Your homes general energy efficiency 

How Often Should AC Cycle Throughout the Day 

You might be wondering if your AC is cycling too often—or not often enough—each time you hear it kick in. In general, you’re probably in the clear if yours is running once or twice per hour, for around 15 or 20 minutes. 

In some cases it may run more or less often, but, again, this will depend on the temperature outside, your AC unit, and the temperature you have set your thermostat to. 

How to Use Design Temperature 

There are some other guidelines that you can use to clock whether or not your AC is running a normal amount. One of those guidelines is by using the “Design Temperature,” of your area. 

Each state has its own “Design Temperature”, which is based on the 30-year average of the maximum temperature. Knowing this helps you determine how and if your AC is running efficiently, and it can help you pick the right unit to handle the average high temperatures of your area. 

Some states have drastically different “Design Temperatures”. For instance, Alabama’s is 93 degrees Fahrenheit, while Arizona’s is 108. 

When choosing an AC unit for your home, it helps to have an expert help you who can find a unit that works with this in mind. 

You can also use your “Design Temperature” to determine how long your unit should be running. However, keep in mind that these recommendations are often based on the assumption that the AC thermostat is set to 75 degrees, so if yours is higher or lower, you may notice your AC is running less or more often, respectively. 

If your area is currently at the design temp, your AC should run the “average” 12-16 hours per day. If it is five degrees higher, it will run 14 to 20 hours per day. At 10 degrees over, it will run 16 to 22 hours per day. At 15 degrees over, it will most likely run all day. If it is five degrees less than the design temp outside, your AC will run six to 12 hours a day. At 10 degrees under, it will run less than four hours a day. 

How Big Should Your AC Be

These numbers are developed with the assumption that your AC is the right size and type for your home. But how do you know what size yours should be? This is where a conversation with a professional can really make all the difference. Together, you can determine exactly what size your AC needs to be based on factors like:

  • BTUs per square feet 
  • Square footage of your home
  • Insulation of your home
  • Whether your home is in full sun or mostly shade
  • Number of windows in your home
  • Design Temperature of your area


If your AC unit is too small, you’ll find that it is working over time to cool off your house. If it is too big, it may end up short cycling, in which it cycles off and on for short periods of time. This is because it cools the air very quickly, and in turn the AC is signaled to turn off. Before you know it, that air has warmed again, and your home begins to rise in temperature — signaling your AC to start all over again. 


Contact us for 24/7 HVAC Services in North Carolina

If you’re a homeowner in Garner looking for HVAC services, you can turn to RS Mechanical. Our team of experts can help you select the right size and type of system for your home. Plus, our emergency services are available 24 hours a day, 7 days a week, to keep you cool all year round. We can provide you with proper AC installation and repair for your home. Call us at (919) 302-8956 to schedule an appointment today or fill out the contact form below to get started.