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Is it okay to leave a central air conditioner on all day?

The short answer is "no." A central air conditioner should only be left on when it's needed, and leaving your AC on all day can reduce its lifespan.

For most homes, the temperature in the house will not change significantly throughout the day. The setpoint of an air conditioner is usually between 74-76 degrees Fahrenheit, so if that temperature never varies, then there is no reason to leave your AC system running all day long.

This means that your AC system will run less, which reduces energy costs and increases your unit's life. Also, turning off your central AC system eliminates any chance of mold growth inside the ductwork.

A sized and installed central air conditioning unit will usually be able to efficiently cool your home when called upon, even in hot weather. During mild weather, you may not need to run the central AC unit at all during the day.

And finally, if your central air system is left on too long without cooling people and surfaces in the house, it can cause humidity levels inside the house to increase above comfortable levels... While only uncomfortable for humans by increasing relative humidity levels, this can quickly dehydrate wood or other materials over time. This means that leaving an AC unit on continuously will eventually rot out floorboards or damage furniture.

With all the benefits of turning off your central air conditioning system, why would you ever want to leave it running?

It's recommended that you set a timer for approximately six hours in the morning and then again in the evening. This will ensure that surfaces and furniture don't get too dry or hot inside your home by controlling humidity levels while not leaving an air conditioner unit on all day.


By following these guidelines, your central AC system should provide ideal temperatures when needed without outside influences affecting the process. The answer is pretty straightforward, no, you should not leave a central air conditioner on all day, which can damage the unit and increase costs. Leave it on only when it's needed!