What Goes into Sizing an AC?

Published on: August 28, 2014
An HVAC tech checking his gauges | AC Southeast®

When buying a new air conditioner, the rule of Goldilocks applies — it shouldn’t be too big or too small but just right. This is the only way to ensure that your home is cooled evenly and that you maintain good energy efficiency. It sounds simple, and it is, but many homes are still less comfortable than they should be thanks to improper sizing.

Why an AC Shouldn’t Be Too Small

An air conditioner that’s too small simply doesn’t have enough cooling power to keep up. By the time the warm days of late spring and early summer arrive, the temperatures will match its cooling capacity and it will run non-stop to keep the temperature in your home stable. This also means that your electric meter will be spinning non-stop. And when summer heat waves arrive, an undersized AC will be outmatched and the inside temperatures will increase throughout the day even though the AC never stops running.

Why Bigger Isn’t Better

An air conditioner that’s too large will only come on for short periods of time before turning off again. That sounds better than running non-stop, but there are some downsides. First, one of an AC’s jobs is to dehumidify the home, but it can only pull humidity out of the air when it runs for long periods of time. Second, if the AC quickly turns off because the area near the thermostat has cooled off, there may not have been enough time for rooms farther away from the thermostat to cool down. This will lead to uneven temperatures throughout the home and decrease comfort.

What Goes Into Proper AC Sizing

When you start to research air conditioner replacements, you may see rules of thumbs such as get 24,000 BTUs of cooling power for every 1,000 square feet. This is a good starting point to get a rough estimate of what you need, but it is only a rough estimate that you’d never want to rely on to make a final decision. There are a number of additional factors that go into properly sizing an AC:

  • Climate: The farther south you are, the higher the summer temperatures that your AC will have to contend with will be.
  • Home layout: Multiple stories, high ceilings, and centrally-located, heat-producing appliances such as ovens are just a few examples of things that could increase your cooling needs.
  • Insulation: A well-insulated home will hold its temperature longer and can reduce your cooling needs.
  • Sun exposure: Direct sunlight can brighten a home, but it also sends heat pouring in that your AC has to deal with.

For a professional estimate of what size AC you need, contact AC Southeast®. We have trusted local contractors conveniently located throughout the Southeastern United States who can help you choose the best AC for your home.