When is constant AC operation a sign of trouble?

[FatimaandAhmed]

Hi all, is it normal for a central AC to run constantly on really hot days, or could that be a sign it’s undersized or needs servicing?

[machinist]

Hi!
It’s pretty normal for a central AC to run for long periods on really hot days. When the temperature outside is very high, the AC has to keep running to maintain the set temperature and control the humidity inside.

However, if it feels like the AC is running all day and the house still does not cool down properly, that could be a sign of a problem. It might be a bit too small for the space, or it could need maintenance like cleaning the air filters, checking the coils, or refilling the refrigerant. Sometimes poor insulation or air leaks in the house can also make the AC work harder than it should.

If the AC is keeping the house cool, long run times during a heatwave can be normal. But if it is not cooling well, it needs to be checked.

[FatimaandAhmed]

Thank you! How do you figure out if an AC is properly sized for your home, and is there a way to calculate what size unit you actually need?

[machinist]

AC sizing is usually measured in tons (cooling capacity), and the basic rule of thumb is around 20 BTUs per square foot of living space. But this is just a rough estimate. Things like ceiling height, number of windows, insulation quality, how much direct sunlight a home gets, and the local climate all play a big role.

For example, a 2,000 sq. ft. home typically needs a 3.5 to 4-ton unit, but if the house is poorly insulated or gets a lot of sun, it might need more.

To get a precise size, HVAC professionals use something called a Manual J load calculation. It is a detailed assessment of a home’s cooling needs, considering all these factors. If the current AC’s size or performance is uncertain, it might be worth having a professional perform this calculation.

But as a simple check:
If the AC runs all day on hot days but keeps the home cool and comfortable, it might be sized fine.
If it is running non-stop and still not cooling well, it could be undersized or need servicing.

Hope this helps!

[FatimaandAhmed]

With all these factors in mind, is there an easy way to figure out if the AC is simply working hard because of hot weather, or if it’s too small for the home and needs an upgrade?

[machinist]

When it is extremely hot, even a properly sized AC will run for long periods. The key thing to focus on is how well it is maintaining comfort inside the home. If the house consistently reaches and holds the set temperature, and all areas feel evenly cooled, then the AC is likely sized correctly and is just working harder because of the weather. However, if the thermostat never quite reaches the set temperature, or some rooms always feel warmer than others, or if the AC seems to run endlessly even on milder days, then it could be undersized or may need servicing.

There is no simple at-home way to precisely confirm if an AC is the correct size because it depends on multiple factors like insulation, window exposure, airflow, and even how much sun the home gets. But as a general rule, if the AC is running constantly and still keeping you comfortable, it is probably fine. If it runs non-stop and still struggles to cool the house, it is a good idea to have a professional do a proper load calculation to figure out if a larger unit is needed or if the current system just needs maintenance.

Hope that helps!

[FatimaandAhmed]

Thanks for the helpful explanation!