Central AC Btu Calculator – What Size AC Unit Do I Need?

What size central AC unit do I need? That’s the question smart homeowners ask as they consider installing a split system air conditioner or replacing an aging unit.

This central AC BTU calculator helps you choose the right capacity for your home. Even if your AC contractor does a BTU load test, this air conditioner BTU calculator will give you a very close idea of the size air conditioner you need.

Getting Central AC Size Right

We get questions like, “what size AC do I need for 2000 square feet?” or “how many BTU AC for 1500 square feet?” This calculator gives you the answer you’re looking for based on house size, climate and other key factors.

The PickHVAC AC BTU Calculator

Here is our AC unit size calculator. Each of the four data – Zone, Size, Insulation and Sun – are explained below. You might find it interesting to see the difference each part makes by inputting different values. For example, all else being equal, a home in warm Zone 1 needs an AC about twice the size of the same home in Zone 6 or 7.

AC Btu Calculator

How to Use the AC Unit Size Calculator

Using our AC unit size calculator is really quite easy. Here’s a step-by-step guide, if you’d like to be walked through the process.

1. Find your Location: The Climate Zone Map is part of the International Energy Conservation Code funded by the US Department of Energy.

Pro Tip: If you’re on a Zone boundary, choose the warmer climate. It is better to have a central AC that is slightly too large than one that is slightly too small.

2. Home Size: Enter your home’s square footage. If you don’t know its size, the information might be found in your closing documents or a blueprint or other drawing of your home. If you end up having to measure your home, measure each rectangle separately and add them up. Double the square footage for two-story sections, of course.

3. Insulation: If you know that your attic insulation is as thick as it should be and your home has house wrap (Tyvek, for example), and you have newer doors and windows, choose Good. If your home is older and/or you feel drafty areas around doors and window, choose Poor. Otherwise, go with Average.

how much attic insulation

4. Sun Exposure: There are two aspects to this. How sunny is your climate? Do you know how many days of sun you get per year? The Mean Annual Sunshine map gives you a good idea. Secondly, how much shade is around your home, especially on the south and west sides, which are usually hot in the summer afternoon? Use these factors to decide how much Sun Exposure your home gets.

Annual Sunshine

The Importance of Proper Sizing a Central AC

Our AC size calculator will help you get it right. Here is an approximate guide for an average home in a moderate climate. 

Room/Area Size:

Recommended BTU:

what size ac unit for 600 square feet

12,000 BTU / 1 ton

what size ac unit for 800 square feet

18,000 BTU / 1.5ton

what size ac unit for 1,000 square feet

24,000 BTU / 2 ton

what size ac unit for 1,200 square feet

24,000 BTU / 2.5 ton

what size ac unit for 1,600 square feet

30,000 BTU / 3 ton

what size ac unit for 1,800 square feet

36,000 BTU / 3.5 ton

what size ac unit for 2,000 square feet

42,000 BTU / 4 ton

what size ac unit for 2,400 square feet

48,000 BTU / 4.5 ton

what size ac unit for 3,000 square feet

60,000 BTU / 5 ton

Our AC size calculator will help you get it right.

Also, if you hire a local certified AC contractor using our Free Local Quotes service, you won’t get it wrong.

The risk of hiring an unqualified, cheap installer is that they will install an AC size that might or might not fit. We won’t belabor the point, other than to say that a central air conditioning system must be the right size to give you the efficiency and indoor comfort you expect.

A central AC that is:

  • Too large will run short cycles since it has more power than you need – cooling beyond the thermostat set point and creating temperature imbalances. They don’t remove as much humidity as a properly sized AC-think “cool and clammy.” That’s not very comfortable! Short cycles also produce a higher risk of mechanical failure.
  • Too small, so it won’t adequately cool your home on the hottest days – or you might find there are rooms on upper levels or far from the indoor system that are noticeably warmer on hot days.

This AC BTU calculator is the first step in getting the right size central air conditioning system to make your home comfortable – the right temperature and perfect humidity.

Central AC Sizes

AC capacity is measured in BTUs – actually BTU/hour, or the number of BTUs the unit moves in one hour of running. ACs shouldn’t run non-stop, but that’s how the measurement is taken.

Residential central air conditioners are produced from about 18,000 to 60,000 BTUs. They are typically in increments of about 6,000 and/or 12,000 BTUs, but not always. The Trane XV18 is an example of a unit sized in increments of 12,000 BTUs. It is available in these sizes: 24,000, 36,000, 48,000 and 60,000 BTUs.

The Trane XR14, one of Trane’s most affordable models, is offered in many more sizes: 17,000, 24,000, 28,000, 34,000, 40,000, 47,000 and 56,000. See all the Trane options in our Trane Central AC Reviews and Guide.

When you use our central AC BTU calculator and know what size air conditioning system is needed, you can discuss options that fit with your HVAC salesperson.

Did you know? Many homes especially in warm climates have more than one central air conditioner. For example, consider a 3500 square foot home in Zone 2 with a Very Sunny rating. It would need between approx. 76,000 and 104,000 BTUs of cooling! The largest residential central ACs are 60,000 BTUs.

In cases like this, either a commercial unit is used or, more often, the home has two or more residential central air conditioners.

An experienced HVAC system contractor can help homeowners in this situation to choose the right size units and divide the home into the best zones. For example, the “sleeping area” of the home is often considered one of the zones while living areas are the other. Another good option is to make the upper floor its own zone, since heat rises, and the second floor might need more AC power per square foot than the ground floor.

There’s More to Choosing an AC than Size

Our BTU AC calculator helps get the air conditioner’s capacity correct.

You might also want to consider the right AC efficiency for your climate and the performance (1-stage, 2-stage or variable capacity) that will give you the indoor climate control you want given the budget you’re working with.  Obviously, the warmer your climate, the more efficient your AC should be. In cool zones like 6 & 7, a highly efficient AC won’t pay for itself. In zones 1-3, it probably will pay you back in 8-12 years.

Our Central Air Conditioner Reviews and Prices Guide might be the most comprehensive Buying Guide available. It is updated annually to reflect current pricing, performance options and much more.

BTUs are Heat, Right? BTUs and Central Air Conditioners

BTUs are British Thermal Units, a measurement of heat. So the obvious question is, “why are air conditioners rated by BTUs?”

As you likely know, the BTU rating of a central air conditioner refers to the amount of heat – the number of BTUs – the unit can remove from your home in one hour.

That’s how an air conditioner works. It cycles refrigerant from the outdoor coil to the indoor coil and back again. In the indoor coil, the refrigerant expands/evaporates and absorbs heat. It carries the heat outdoors – the outdoor unit is called the condensing unit.

There, the heat is released in the outdoor coil, a radiator-like piece of equipment. The heat disperses out of it, and the fan helps cool the coil.

Other HVAC Size Calculators

We’ve also produced BTU calculators for:

Heaters/Furnaces

Window and Portable Air Conditioners

Our goal is to help you determine the right equipment size for your home. When the size is correct, the equipment will give you the most comfortable heating and/or cooling for your home. 

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