Advanced Air

What Size Air Conditioner Do I Need for My Southwest Florida Home?

January 11, 2016

Need a new air conditioner for your Florida home? Wondering what size to get? You’re in the right place.

In this article, we’ll show you:

  • Why the right air conditioner size is so important
  • How an air conditioner's size is measured
  • How to get the right sized AC

Why a correctly sized air conditioner is so important

When you buy a new pair of shoes, do you purchase ones that are too small? Probably not. They’d crush your toes. And shoes that are too big would trip you (or just fall off your feet).

Buying the wrong size air conditioner has similar consequences. For example...

An air conditioner that’s too small will run non-stop and never cool your home to your desired temperature.

An an air conditioner that’s too big will short cycle. That means it will turn on, cool your home very quickly and then shut off. While this might seem like a good thing, it actually results in:

  • Increased energy bills. Just like your car gets better mileage on the highway than in stop and go traffic, long run times are more efficient for your AC.
  • Hot/cold spots in your home. Since the fan doesn’t run very long, it doesn’t have time to circulate the air throughout your home evenly, creating uneven temperatures in your house.
  • Shorter lifespan. The frequent turning on and off wears out the air conditioner parts more quickly, leading to a shorter lifespan.

So now you know why the right size AC is so important. But before we get into how to find the right one for your home, let’s look at…

Tonnage: how AC size is measured

An air conditioner’s size is a measure of its cooling capacity, or how much heat it can remove from the air, (not its physical size/dimensions).

Cooling capacity of air conditioners is measured in tons or BTUs (British Thermal Units). 1 ton of cooling is equal to 12,000 BTUs. (BTUs are a measure of energy where 1 BTU is the energy needed to raise the temperature of one pound of water by one degree Fahrenheit.)

Home air conditioners range in size 1-5 tons in half-ton increments (1, 1.5, 2, 2.5, etc.), with 1 being the smallest size.

So how do you know what size you need for your home? You need to know the amount of energy necessary to cool the air in your home. And that requires a heat load calculation

Determining the AC size with a heat load calculation

A good air conditioning installer will perform a heat load calculation to determine the correct size AC for your home.

A heat load calculation is a complex algorithm that takes into account your home’s:

  • Location
  • Insulation levels
  • Construction materials
  • Size and layout of your home
  • Height of ceilings
  • Orientation of home (north-south, east-west, etc.)
  • Size, location, age and type of windows
  • Size, location and orientation of rooms
  • Number of people in the home
  • Type of roof
  • And much more

If you want to see how complicated this calculation is, check out this online calculator for yourself.

Beware: rules of thumb

Run if you hear your AC installer say something like, “You need 1 ton of cooling for every 500 square feet in your home.” Every home is different and there is no single magic formula. Rules of thumb like this lead to oversized air conditioners.

As one of our colleagues explains:

“What we find is that most newer homes come in no lower than 800 square feet per ton... High performance homes can be as high as 1500 or 2000 square feet per ton. That means that a contractor using 500 square feet per ton is installing an air conditioner that's 2, 3, or even 4 times larger than it should be.”

Energy Vanguard (emphasis ours)