How Long Can You Run a Window or Portable AC Continuously?

A window AC or portable air conditioner can run 24 hours a day, 7 days a week without shortening its average lifespan. Running continuously will not cause overheating, excessive wear and tear to the unit, or any other damage that will shorten its life.

How Long Can You Run a Portable or Window AC Continuously

Indefinitely. It isn’t running that causes the most damage – it is turning on and off. As one HVAC technician put it, when an air conditioner is properly sized, “we want the condensing unit to run all the time, a hundred percent of the time with no cycling [off and back on].”

Manufacturers’ warranties are based on a consideration of the number of times the unit starts rather than on how long the unit runs. In fact, if you keep the unit well maintained, you can expect to see a lifespan of up to 50,000 hours of use.

Is it Better to Run the AC Continuously or in Intervals?

It is better to leave the air conditioner running continuously. When an air conditioner runs with frequent cycles or is turned off and on repeatedly, it creates wear and tear to the compressor and will shorten the life of the unit.

Air conditioners that run on short cycles because they are oversized for the application, which means they start and stop frequently, will not last as long as units that run for long periods.

Inverter Variable Speed Air Conditioners Are Made to Run Continuously

With a single speed or non-inverter type AC, the system turns on full blast and continues running at full capacity.  When the desired temperature on the thermostat is reached, the compressor turns off. This is hard on the compressor. From a climate control perspective, a lot of on/off cycles can cause temperature swings that might be noticeable. Plus, an AC that runs in short cycles doesn’t remove as much humidity. The result can be a cool, clammy feeling in the air.

Finally, starting the air conditioner frequently uses more energy than leaving it running.

An inverter AC can run at capacity anywhere from about 25% or 40% depending on the unit to 100%. And it will run at the lowest capacity needed to keep up with the cooling demand.

When the room temperature reaches the set temperature on the thermostat, the inverter AC lowers the capacity to a level that will maintain the set temperature. The AC continues to run at that power level preventing the indoor temperature from rising.  This keeps the room more comfortable, better dehumidified, and actually saves energy even though the unit may be running continuously.

Why Does My AC Compressor Continue Running Without Any Cycles or Stops?

Two common reasons the compressor runs all the timer are AC design and outdoor temperature.

1). An AC with an inverter compressor is designed for longer, even continuous, cycles. That’s a good thing, reducing mechanical wear, extending the air conditioner’s life and creating a more comfortable indoor environment.

2). The outside temperature is very high, and the unit needs to run all the time to keep up.

As we’ve noted, an inverter AC will commonly run continuously instead of cycling on and off. When the desired indoor temperature is reached, the unit runs at a lower speed to  maintain the desired temperature.

Buying tip: If you live in a region where the temperature is often above 95F, purchase a portable or window AC that is slightly oversized. Don’t rely on the general rule of 20-25 BTUs per square feet.

When sizing a room air conditioner, consider your square footage, of course, but there are other factors that affect an air conditioner’s ability to cool the room:

  • How well insulated your space is
  • How many windows you have (more windows, more heat inside)
  • How much direct sunlight you receive (does the room face west?)
  • How many people live in the home or usually occupy the room – people create a lot of heat.

An HVAC professional or knowledgeable salesperson can guide you on properly sizing an AC based on your situation.

An air conditioner might also run continuously if the air flow is blocked from a dirty filter or the unit needs repair or maintenance. Dirty coils, low or leaking refrigerant, a faulty thermostat, or the AC being very old are also reasons an air conditioner may run constantly. But these aren’t good reasons the AC runs all the time. A well-maintained AC will cost less to operate and will be more durable.

Why Does the AC Fan Continue Running After the Room Has Reached the Desired Temperature?

It is normal for the AC fan to run for a couple of minutes after the compressor has shut off. It does this to blow the last of the cooled air into the room. If it runs for a long time without the compressor kicking on, check if the AC is set to Fan Mode, which will run continuously.

The fan running continuously will not harm it. It uses very little energy. Running the fan when the compressor is off helps circulate the air creating a more even distribution of the cool air. Less frequent starts and stops of the fan can extend its lifespan.

If the fan continues running for longer than a minute or two after the compressor has turned off and you’ve set the AC on auto, meaning the fan will only run when the compressor is on, it could mean several things including  that the compressor isn’t working or isn’t receiving power.

My AC Runs All the Time – Is that OK?

On a very hot, humid, day, it’s best to allow your air conditioner to run continuously. If the AC reaches the desired temperature, it will turn itself off, but it’s not going to save you much money to manually turn it on and off. This creates wear and tear on the compressor and can shorten its life.

Turning your AC off when you are gone will not save much energy either because when you return to a hot room, the air conditioner will have to run much longer to cool the overheated room. When an AC runs constantly it will control the humidity better creating a more comfortable environment.

Can You Leave a Portable Air Conditioner Running When No One is Home?

Yes, you can leave a portable air conditioner running when you are not home. Some online posts do say no, but those are primarily concerned with energy usage. An AC will obviously consume more energy when it’s running than when it’s turned off. But leaving a portable or window AC running will not damage it or cause it to overheat and catch fire.

If you have a portable AC, running it when you are not home is fine with some considerations. If you don’t have a hose to drain the condensation the unit collects as it dehumidifies the air, make sure the condensate tank is empty before you leave.

Also, make sure that your portable air conditioner has a proper, dedicated plug so it won’t blow a fuse or cause a short.  And check to make sure the filter is clean as well.

If you plan to frequently leave your portable AC running when you’re not home, for instance while you are at work, consider an inverter unit. An inverter AC will run on a lower speed once the desired temperature is reached, running just enough to maintain that temperature. This will save more energy than running it all day at full speed.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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