How to Determine the Right Size AC Unit for Your Home

We have heard a lot about how your AC system should be the right size for your house in order for it to work most efficiently. Yet most people still have no idea how to perform the right calculations to figure out the correct size. It is not an easy task indeed. But the concept is pretty simple to understand.

Your required AC size depends on a few conditions. Here are some of the key factors:

– Room Volume

The first thing you need to know is the area of the interior of your home in square feet. The height from floor to ceiling matters too. If your house has no blueprints, you can measure it manually.


British Thermal Unit is a unit of measurement that represents the energy required to increase or decrease temperature. Approximately, a square foot of room requires 25 BTUs. If your room height is over 8 feet, multiply the BTU by 25%.

For example, if a room is 30 x 50 square feet with a 7-foot ceiling, that would be 37,500 BTUs. You can also convert the measurement to tons by dividing it by 12,000. For this sample house, the result would be about 3 tons. That is the exact AC size you need to look for.

However, that is just a simple calculation. Professional technicians will include more factors in their calculation, such as:

  • Number of people living in the house
  • Windows and opening situation (how many, how large, how old, and which direction they face)
  • Existing ventilation system
  • Vegetation around your house

Calculating all of this can be pretty complicated. Hence, it is better to leave the job to professionals.

How can I be sure my system is the right size AC unit for my home?

A perfectly sized AC unit will be able to run its full cycle. Hence, it can provide stable comfort for a long time. The coldness will spread evenly throughout the entire room. At the end of the month, your energy bill will be reasonable.

If your AC unit is too big, you will notice that your room will get cool pretty quickly, but the machine will frequently turn on and off as it fails to finish its cycle. An oversized AC will cause you to have higher monthly bills.

On the other hand, if your unit is too small, your AC will not make your home as cold as you expect it to. The coldness will not spread evenly either, which can be noticeable. The machine will have to run continuously and harder to reach your ideal temperature, but it will be unlikely to get there. Hence, it will be a waste of energy.

It is fine if you don’t understand the calculation for your appropriate AC size, as long as you don’t completely ignore it. If you need professional help, make sure they are certified, so you know for sure that they have the expertise to perform a careful and accurate calculation. Making an effort to choose the right size AC unit for your home will save you a lot of money in the future.

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