“Your home is 1,500 square feet, so you need an AC with 30,000 BTU’s.”
If you run into companies or techs who have said something similar, BEWARE.
Sizing your new air conditioner based solely off of square footage is never the best option. That method is a rough estimate (at best), but not exact. If you only base your sizing decision on square footage, you’ll likely end up with an AC that’s under or over-sized.
Hint: Over-sized/undersized AC’s cost you a LOT in the long run.
And if you’re about to drop several thousands on a brand new AC, you might as well size it correctly, right?
So what’s the “correct” way to size an AC? Well, the only way to get an accurate AC size is to have a professional perform a “cooling load calculation.”
Don’t worry—we’ll explain what a cooling load calculation is, and we’ll also go into more detail about how AC size is measured. The following is an overview of what we’ll cover in this article:
- BTU’s & Tons: How AC size is measured
- Why you need a correctly-sized air conditioner
- A cooling load calculation: The only accurate way to find the right size AC
Want a professional to answer your AC sizing questions?
BTU’s & Tons: How AC size is measured
When we talk about size, it’s important to know that air conditioners are sized according to how much heat they can remove from your home—not their actual physical dimensions.
So the “bigger” the AC, the more heat it can remove from your home.
Now AC size is expressed by either…
Note: Both BTU’s and tons mean the same thing—they both refer to the same size, they’re just a different way of expressing that size.
A BTU (British Thermal Unit) is a measurement of heat. More specifically, 1 BTU equals the amount of heat energy needed to heat 1 pound of water by 1° F. Most air conditioners in Kansas City range from 18,000 to 60,000 BTU’s.
So an air conditioner’s “BTU output” simply refers to the amount of heat it can remove in one hour.
To simplify those large numbers, you’ll often see AC size referred to tons. 12,000 BTU’s equals 1 ton. Most AC’s range anywhere from 1 to 5 tons (increasing in increments of 0.5—i.e. 2.5, 3.5, 4.0, etc.).
Below is a chart to help you quickly compare BTU’s with tonnage:
- 12,000 BTU’s = 1 ton
- 18,000 BTU’s = 1.5 tons
- 24,000 BTU’s = 2 tons
- 30,000 BTU’s = 2.5 tons
- 36,000 BTU’s = 3 tons
- 42,000 BTU’s = 3.5 tons
- 48,000 BTU’s = 4 tons
- 60,000 BTU’s = 5 tons
Why you need a correctly-sized air conditioner
When it comes to air conditioner size, bigger isn’t always better. Like a shoe fits a foot, the AC size needs to fit your home’s cooling needs. No more, no less.
In fact, getting an AC that’s too big or too small for your home leads to the following problems:
- An under-sized air conditioner means you’ll be uncomfortable during the summer because it will struggle to cool your home to your thermostat setting. The AC will run longer, leading to higher energy bills, frequent repairs and a premature breakdown.
- An over-sized air conditioner will cool your home quickly and then shut off (this problem is called “short cycling”). If your AC cools the home too quickly, it won’t run long enough to properly dehumidify the home, leaving you uncomfortable—even at a lower temperature setting. Plus, you’ll waste energy and lower the system’s lifespan because the AC turns on and off frequently.
A cooling load calculation: The only accurate way to find the right AC size
Like we mentioned in the very beginning, the only accurate way to find the high AC size for your home is to have a professional perform a cooling load calculation.
A cooling load calculation takes into account the following factors:
- Square footage of your home
- Materials used in the construction of your home
- Structure of your home (for example, if you have vaulted ceilings)
- The climate zone you live in
- Number of windows, doors and skylights in your home
- Home’s orientation in relation to the sun (east-facing, north-facing, etc.)
- How well your walls and attic are insulated
- The condition and quality of your duct work
- How many people live in the home
- And much more
Once a professional knows all of these factors, they can recommend the right size air conditioner you’ll need for your home.
Need help sizing your AC? Ask our Kansas City pros
We’ll perform an in-home cooling load calculation—for FREE—so you know exactly what size air conditioner you need.