Summer days and even nights can be hot (even above 90°F). To fight the heat, we use air conditioners. When it’s consistently hot and we need continuous air conditioning, we start to have questions like ‘how many hours should AC run per day?’ and ‘how long can AC run continuously?’.
The basic principle of if you should run an AC unit continuously is fair simple:
- We can’t live comfortably in hot homes.
- The only job AC units have is to lower temperatures (they also reduce moisture levels; we will talk about the con of this in the section about how long can AC run continuously).
- If it’s uncomfortable hot, we have to use AC units continuously or until the indoor temperature is agreeable with our comfort levels.
This is unfortunately not information we can get from the specs sheets. No spec sheet will say ‘you can run this portable air conditioner for up to 12 hours per day’. We run air conditioners when it’s hot. What happens if it’s hot all throughout the day or even 24/7?
Singapore Example: In June 2021, the average temperature in Singapore was between 76°F and 91°F. Based on ‘Duration Of Air Conditioner Use Per Day’ study by Statista, most people run an air conditioner between 3 and 6 hours per day (41% of respondents). 25% of respondents said they run an air conditioner between 1 and 3 hours per day, and 34% of respondents said they run their AC for more than 7 hours per day
Here’s the deal:
Some homeowners run their air conditioner for 1 hour per day and others run their AC units continuously. Is it OK for AC to run all day? There are no generally set directions from institutions like the Department of Energy (DOE) or Energy Star on how many hours should you run AC per day.
We can, however, give some practical directions on how many hours per day should you run your AC given the outdoor temperature.
Example: If the temperature day highs are in the 90s and the lows in the high 70s, you should run an AC for about 8 hours per day. The daily temperature should be about 75°F during the day and about 72°F during the night.
What is more, we can use estimated yearly electricity use (found on the EnergyGuide label) as a guiding point on how long should you run an AC per day.
Of course, running an air conditioner all the time (24/7) has its cons as well. We are basically overwhelming the AC unit. We will look into 3 aspects of air conditioning running hours, namely:
- How many hours per day should you run your AC? We will look into some guidance on how many hours per day it makes sense to run an AC unit (depends on how hot it is).
- How long can AC run continuously? We have to check if it’s normal to run AC run continuously and if AC units are actually engineered to be able to run continuously for days on end.
- Disadvantages of running an air conditioner 24/7 for days or even weeks. These include increased wear-and-tear and running costs, shorter AC lifespan, and problems with dry air.
Let’s start by looking at recommended AC running hours per day:
How Many Hours Should AC Run Per Day?
Let’s say that we can’t comfortably live if the indoor temperature is above 78°F. When we run an AC unit, the temperature falls below 78°F. When we shut off the AC, the indoor temperature can shoot over 78°F pretty quickly.
Here is the general rule on how many hours per day should you run AC:
If you find the indoor temperature too high, you should run your AC unit. Here are rough directions of how many hours per day makes sense to run an AC:
- Run an air conditioner for 2 hours per day if the highs are in the high 80s and lows are in the 70s.
- Run an air conditioner for 4 hours per day if the highs are in the low 90s and lows are in the high 70s.
- Run an air conditioner for 8 hours per day if the highs are in the high 90s and lows are in the low 80s.
- Run an air conditioner for 12 hours per day if the highs are in the low 100s and lows are in the 80s.
- Run an air conditioner for 24 hours per day (continuously) if the highs are consistently above 100s and lows are in the high 80s or even 90s.
This is are not government-directed running times. It’s just a rough estimate of how many hours per day a majority of homeowners run their AC unit in the summer.
Nonetheless, we have some government guidance, as mentioned before. Here is an example of an EnergyGuide label for a popular window AC unit:
When they calculate the running costs, Energy Star always presumes that we will run an air conditioner for 8 hours per day (and for 3 summer months). Here we have to understand that these electricity expenditures have to include conditions of running an AC unit that is closest to how long we practically use air conditioners.
That simply means that the assumed use of the AC unit is 8 hours per day. This is the best indication we have of how long AC units are expected to run per day.
Of course, as we see from the running hours per day recommendation above, we usually run an AC for more than 8 hours per day in hot weather and less than 8 hours per day in merely warm weather.
Now, one of the key questions we need to answer is about how long can AC run continuously:
How Long Can AC Run Continuously?
AC units are engineered to be run continuously.
Technically speaking, air conditioners are quite robust. The main part of the AC – air compressor – is a device that can run 24/7 without a fault.
Of course, there is a difference in the durability and reliability of air compressors used in different types of air conditioners.
The question of ‘how long can you run a portable air conditioner continuously?’ and ‘how long can you run a mini split continuously?’ does not always yield the same answer.
Mini splits are very reliable. You can run a 2-ton or 3-ton ductless mini split for days or even weeks on end without any problems.
You can also run a portable AC unit continuously for days on end but you run into a higher risk of portable AC failure. For example, it is not recommended to run a portable or window air conditioner continuously for a whole week.
Here is the practical aspect of running any air conditioner continuously:
If it’s too hot to live in your home, you have to run an AC unit all the time.
There is just no way around it. It’s not like we have other sources of cool air. If we want a comfortable temperature in our home during a summer heatwave, AC units usually have to be run continuously (even at night).
The pro of running an AC unit continuously is apparent to all:
We get comfortable living temperatures.
What you have to take into account, however, are the cons of running an AC all the time:
Cons Of Running AC Continuously
The majority of key AC specs – lifespan, power consumption, expected humidity levels – are calculated based on an 8-hour use during a 3 month period.
For example, we know that window air conditioners last for about 10 to 15 years. However, this is if we use them for 8-hours during a 3-month period.
Obviously, if we run an AC continuously, we run into some apparent issues. These include:
- Decreased lifespan due to increased wear-and-tear. If we run an AC too much, the expected lifespan of air conditioners you can check here are inevitably decreased. A good analogy is if you have two same 5-year cars: one has 20,000 mileage and the other has 100,000 mileage. It’s quite obvious that the increased wear-and-tear will reduce the expected lifespan of any AC, be it portable, window, mini split, or central air unit.
- Increased cooling costs. If you run an air conditioner all the time, you will see a spike in your electricity bill. In the above EnergyGuide example, we see that the expected yearly cost of running an AC is $125. That is if we run it for 8 hours per day. If we were to run it for 24 hours per day, the running costs would triple to $375.
- Running AC continuously can cause dry air. If you check how portable air conditioners work here, you will see that every AC unit reduces relative indoor humidity levels. Even if you only use it continuously for 8 hours, you might see the moisture levels dip below 40%. If you run an AC continuously for days, the indoor relative humidity can fall even more (below 20%). We will experience this as very dry air and most of us find such low humidity levels fairly unpleasant.
Needless to say, if we desperately need our AC to run 24/7, we will have to face these disadvantages.
That doesn’t really mean that we can’t run an AC all the time. We just have to keep in mind that we will have to pay the cost for overwhelming our air conditioning system.
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