An AC should run 12 to 16 hours a day on average summer days when the air conditioner is properly sized.
On the very hottest days of summer, don’t be surprised if your AC runs 20 hours or more, especially if the weather is well above the normal heat range.
What Determines How Many Hours of AC?
How long your air conditioning runs each day is affected by a number of things including:
- The outdoor air temperature
- The temperature your thermostat is set to
- The air conditioner’s size
- What type of air conditioning unit you have
- The amount of insulation in your home and other factors related to your home’s energy efficiency
In general, a properly sized single stage (one speed) air conditioner will run in 15 to 20 minute cycles throughout the day, one to two per hour, and sometimes three, depending on how hot it is outside.
These cycles will come to about:
- 8-14 hours total run time for central air
- 12-18 hours run time for a window unit
- 16-24 hours run time for a portable air conditioner
Below we provide you with all of the details so you can answer the question based on your own circumstances.
What is Design Temperature?
We’re answering this now because the term is important for later. Your AC’s size should have been chosen by an HVAC contractor with your location’s specific design temperature in mind. This means that if they did their job, they should have selected an AC “design” with your annual hottest “temperature” in mind.
Let’s explain a little more.
Design temperatures are specific to the area where you live. Arizona’s design temperature is 108. Michigan’s is 86. It’s not hard to understand the difference, right?
Design Temperature is based on a 30-year average of the maximum temperature that the area gets for 99% of the hours of the year.
There are 8,760 hours in a year. If the Design Temperature of your area is 92F, you should only get 1%, or 88 annual hours, where the temperature rises above 92F.
The higher the temperature is, above the Design Temperature, the more hours per day that your air conditioner will run. The chart below will give you an idea of how this works and then you’ll find a list of the Design Temperature for every state in the US.
Average Design Temperature By State:
|1.0% Cooling Temperature (°F)
|1.0% Cooling Temperature (°F)
|District of Columbia
|Northern Mariana Islands
|Virgin Islands, U.S.
You can check the accurate design temperature by county here.
How Many Hours Per Day Should the AC Run?
Find the Design Temperature for your area in the chart above.
Now, use the chart below to answer the question – How many hours per day should the AC Run?
Start with the column on the left. For example, if the outdoor temperature is at your Design Temperature for your state, the AC will run about 12 to 16 hours each day.
You’ll see that as the outdoor temperature rises above the design temperature, the AC will run more, and as the outdoor temperature goes down, the AC will run fewer hours each day. This chart is based on a single-stage, central air conditioner keeping the indoor air temperature at 75F
How many hours per day should the AC run per day?
|Average Outdoor Daytime Temperature
|How Many Hours AC Runs Per Day
|Design Temp + 15 F
|Design Temp + 10 F
|16-22 hours per day
|Design Temp + 5 F
|14-20 hours per day
|12-16 hours per day
|Design Temp -5 F
|6-12 hours per day
|Design Temp -10 F
|Less than 4 hours
Note: The indoor temperature is based on 75 F. Design temperature is based on Manual J/D and ASHRAE 1% cooling temperature. This chart can be used for single-stage central air conditioners, non-inverter portable ACs and non-inverter window ACs. Other factors like humidity and sunlight can also impact the running time. Also dirty filters, leaking ducts, undersized units, etc. will extend the running hours per day.
A Properly Sized Air Conditioner
Whether your air conditioner is properly sized is the most important factor in how long your AC runs and how comfortable it keeps the air in your home.
BTUs per square feet is not the only factor when properly sizing an air conditioner. You, or an HVAC tech, will need to consider the square footage of your home but also how efficiently your home is insulated, is the home shaded or in full sun most of the day, the number, age, and placement of your windows, how many people live in the home, and the Design Temperature of your area.
An Air Conditioner That is Too Big Doesn’t Run Long Enough
An air conditioner that is too big will run for less than 10 minutes each cycle. The air becomes cool and the unit turns off, but quickly warms again, because it hasn’t cooled down your house. The walls, furniture, flooring all retain heat, and so when the AC is off, the heat in those items heats the air. And the AC turns back on.
This is called “short cycling”. An air conditioner needs between 15 and 30 minutes run time to completely cool and dehumidify the indoor air, and over time, the structure and items within your home.
Specific run-time depends on the outdoor temperature, the size of your home, and insulation. When the AC short cycles, the air will remain humid and the temperature will be inconsistent, leaving you uncomfortable.
An Air Conditioner That is Too Small Runs All the Time
An air conditioner that is too small will not be able to cool the indoor air to the desired setting, especially when 100 degrees outside or hotter, and will run at 100% power constantly.
Other Factors That Cause the Air Conditioner to Run Longer
There are other reasons that your air conditioning system might run longer than it should – reasons not related to design temperature or outdoor temperature. They include:
- Restricted air flow due to a clogged filter or a blocked vent
- A dirty or poorly maintained AC
- Undersized or damaged ductwork
- Leaking or low refrigerant.
How Long Does My AC Run Each Day?
Manually tracking how long your AC runs each day would be a time consuming task, but there are smart thermostats on the market that will easily accomplish this for you.
Google Nest and Ecobee are both smart thermostats that keep track of your HAVC system including how long the AC runs each day. Google Nest can track for up to 10 days, but if you’d like to keep track for an entire season, or even year, consider the Ecobee which can track HVAC performance for up to 18 months.
Will a Two-Stage or Variable-Speed/Inverter AC Run Longer?
Yes it will, and it will be more efficient than a single stage AC unit. Standard or one-speed air conditioners always run at 100% power, and when the desired indoor temperature is reached, they turn off. The indoor air warms up again, how quickly depends on the outside temperature, and the AC turns back on again, cycling like this throughout the day.
Short cycles are hard on the compressor, shorten the life of the AC, and use a lot of energy.
A two-stage air condition has a 100% capacity setting and about a 60% to 70% setting, but a variable speed unit can run at any capacity using only the power needed to maintain a consistent temperature in the home.
So, a two-stage or variable speed air conditioner will run longer, and possibly even all the time, but it will keep your home more comfortable, less humid, save energy costs, and reduce wear and tear to the compressor.
Is There Any Disadvantage to Running the AC Continuously?
If you have a properly sized single speed unit or a two-stage or variable AC, then no, there are no disadvantages. In fact, running constantly, rather than frequent on-off cycles, will actually extend the life of the unit.