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Determining What Size Air Conditioner You Need

Posted on June 6, 2019
by Appleby Systems

Question mark regarding house

Buying the right sized air conditioner is important. You might be tempted to buy a larger air conditioner thinking that will be the best way to keep your home cool. Or maybe you want to try and save a few bucks by picking up an AC that’s on the smaller size.

In either case you’re probably not getting exactly what you want. Oversized and undersized ACs may be inefficient for different reasons, but in the end they both lead to uneven cooling and inefficiency (read: higher bills). Not to mention, oversizing or under-sizing also leads to frequent stopping and starting of the air conditioner, causing more wear and tear and resulting in reduced life span of the equipment.

So how can you fix this and determine the correct size AC that you need? Find out more below.

How Do I Find the Correct Sized AC Unit?

The capacity of an AC is measured in BTUs (British Thermal Units) – a measurement you probably don’t use every day. There are two ways you can calculate how many BTUs your home requires:

  • Manual J Calculation. This is the more precise method. It considers a variety of factors; everything from climate to the quality of insulation, even natural sunlight and the amount of people that use a room. Many utility companies will account for these factors (and others) in their calculation of your home’s needs. You can also reach out to an HVAC expert that can use this calculation to find the AC unit size best for your needs.
  • Square Footage. Alternatively, you can cross reference your home’s square footage to get your AC per square foot. This is a less precise, but still serviceable method of finding what size AC unit your home requires. Once you have determined your home’s square footage you can cross reference that number with a chart showing the recommended BTUs.

Different Air Conditioner sizes for homes

Using an Air Conditioner Calculator to Determine BTU Per Square Foot

If you want a more accurate measurement without having a professional come in, you can use a BTU calculator. This BTU calculator, for example, adds ceiling height to your square footage equation so that you are estimating what AC unit size you need based on a third dimensional idea of the space.

Additional Tips

Here are a few other quick methods you can choose to factor in if you are not using a calculator or the Manual J Calculation.

  • In a very sunny room, increase the capacity of the AC unit by 10 percent. Decrease by 10 percent for very shady rooms.
  • For the kitchen, remember that the appliances generate heat. Add around 4000 BTUs if you’re looking to heat this room specifically.
  • If the room will often have more than two people in it, add 600 per person.

Aside from doing heat loss/gain calculations for homes to determine sizing, we generally allow 1 ton of cooling for every 900 square feet. For your comfort, it’s best to buy a unit on the higher end of your estimate. The maximum would be 15 percent over the estimated BTU before it becomes too big.

Don’t be shy about contacting us to help determine what size AC you need for your home. We’d be happy to answer any questions and set up an appointment to get a better understanding of your needs.

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