Is It Safe to Leave an Air Conditioner On Unattended 24/7?

Walk into your home after hours outside and you will be greeted by a blast of warm or cold air depending on the season.

This is one of the reasons why you may want to turn on your A/C system before leaving for a long trip.

It can be an energy-saver as well: it takes more energy to cut the air conditioner on/off every time you need it than letting it run for a long time at a specific setting.

So, Is It Safe to Leave an Air Conditioner On Unattended 24/7?

The straight answer to that question is “no” although a few factors may come into play, such as the quality and type of the unit.

Here is why it’s unsafe to leave the device running for that long:

1. Window Air Conditioners Are Prone to Fires

Never let a window air conditioner run unattended 24/7. This class of air conditioners is the likeliest to cause a home fire.

Most of the home fires caused by window A/C units are attributed to problems in the electrical wire or sometimes the insulation materials covering the wires or both.

Often, the culprit is the extension cord that links to the window unit to the power source.

Extension cords link the window A/C unit to the power outlet on the wall.

The issue, however, is that residential extension cords (plus their surge protectors) are mostly rated for minor electronics.

They are seldom rated highly enough to service a window A/C unit.

That’s why window air-con units are prone to fires, and almost always start somewhere on the cord or wall outlet.

If such an electrical mishap occurs when you are away – say, you left the unit turned on on your way out for a 1-week outing – chances are you will return to a scorched home.

It is important that a homeowner planning to use this kind of air conditioning unit understand the risks and how to avoid them.

2. UNSAFE If Your A/C Unit Is Old and You’re in A Heat Wave

The worst time you could leave the unit running that long is when everyone in the neighborhood is using their units.

During heat waves, for example, when more people in your neighborhood are running their air conditioning units at high power settings simultaneously, the unit can trip your circuit breaker or cause a power outage/brownout on your block.

This is especially likely if your air conditioner is older and sucks more power than an average energy-efficient system.

Also, old units are highly vulnerable to short-circuiting which often causes the system to overheat with time and subsequently ignite.

Another culprit is frequent power fluctuations or surges in voltage – it can cause overheating which may progress into a major fire if no one is around.

The worst thing that could happen to anyone is losing the A/C unit during a searing heatwave.

If you have family members or pets that can’t tolerate heat, you need to find another solution fast enough to avoid it.

If you are aware that most people in your neighborhood are running their air conditioners during hot weather, don’t think of leaving yours running 24/7, or even a full day unattended.

3. UNSAFE If You Don’t Want to Bloat Your Electricity Bills

Whether leaving the air conditioner on 24/7 is safe for your electricity can depend on a range of factors. Generally, it is unsafe.

The best way to find whether your system won’t suck a lot of power during this long period is to obtain personalized advice from your local Gold Star Services A/C technician.

For many users, leaving the unit active for extended periods may actually be a money-saver and more efficient than having to turn it on/off often.

One of the easiest ways to bloat your electricity bill is to strain your unit by turning it on/off way too often.

Fortunately, most modern devices can be programmed.

This removes the need to choose between leaving the running at a specific temperature or turning it off.

Depending on your room conditions and situation, raising and reducing the temperature by a small range of degrees at specific times can be the best and most efficient practice for your machine.

4. Your AC Doesn’t Fit the Size of the Room

The surest way to waste your electricity (and money) is to run the unit for too long without knowing the unit is too small or big for the room.

But, how do you even tell if the unit isn’t the right size?

If it struggles consistently meeting the specific temperature you set on a timely basis, then chances are it is small for the room. In such a case, it will need to run longer to attain your set temperature.

Conversely, an oversized AC will keep cycling between on and off (called “short-cycling”).

Other than bloated electricity bills, either of these two situations may also wear down your air-con faster.

So How Long Should the A/C Unit Run?

Assuming your air conditioner is the right size for your room, it should cool it in a 15 – 20-minute cycle. During warm weather when the air is hot or wintertime when the air is humid, it will likely take longer to achieve your preferred temperature.

Measure the amount of time it takes to achieve your desired temperature.

If the device runs for up to 20 minutes without changing the room’s temperature, chances are the machine is too small or inadequate for the room.

In this case, you will need to upgrade to match the size of the space.

An A/C system that is larger than your room will short cycle to cool your space too quickly, in just 10 minutes or less.

Achieving a cool temperature point faster may sound beneficial, but this short cycling could mean your machine won’t effectively reduce the humidity in the room, leaving you feeling sticky and hot.

Even worse, the device will become overworked, start to break down too often, and demand costly repairs or replacements.

What are the factors Impacting the time taken by the Air Conditioner to cool the room?

They are numerous. Some of the things you’d take for granted like the location of the device may have a considerable impact.

Here are some of the most impactful factors:

1. The temperature outside

If it is hot outside, the air-con will need to operate longer to reach the desired temperature.

2. The thermostat’s setting

If you set it low in the summer, it will take a long time to achieve it

3. The size of the air conditioner

The bigger the air-con, the faster it will achieve the set temperature

4. The state of the air conditioner

If you care for your machine well, it will keep operating efficiently for longer.

The long lifespan means you don’t need to invest in a new product too early.

A badly run or neglected machine does the opposite

5. The size of the home

The larger the home the longer it will take to cool. This can be even worse if the air-con is smaller than what the home needs.

6. The insulation on the home

The absence of quality insulation on a home means much of the cool air ends up leaking outside.

This means it will take such a long time to cool the rooms.

The idea of leaving the unit running all day brings one thing into the mind – fire.

However, the good news is that the least likely appliance to start a home fire is your air conditioner although it’s going to depend on the type and other factors.


So, is it safe to leave an air conditioner unattended 24/7? The answer to that question is “no.”

If you own a window air conditioner, never leave it active and unattended – this type of air-cons is prone to fires.

Depending on other factors, leaving the air-con of any kind running can bloat your power bills.