Sizing an Air Conditioner

A photo of a service consultation

What Size Air Conditioner Do I Need to Cool My House Efficiently?

An undersized air conditioner can struggle and struggle—using tons of extra electricity—and never fully cool your home. Instead of suffering a muggy Naples summer with an air conditioner that can’t beat the heat, learn about the air conditioner sizes best for a home or apartment.

What Is BTU in Air Conditioners?

BTU stands for British Thermal Unit, the unit of measurement commonly used to describe air conditioner size alongside tons. BTUs measure the amount of heat used to change the temperature of one pound of water by one degree. A 25,000 BTU air conditioner absorbs 25,000 units of heat in one hour.

We use BTU alongside tons because they measure different things. The tonnage of an air conditioner describes the capacity of heat your unit can remove from a space. A one-ton system removes 12,000 BTUs in an hour.

What Size Central Air Conditioner Do I Need?

To find the air conditioner size that will work for your home, hire an HVAC professional who knows how to calculate air conditioner size for a house or apartment. They’ll start by calculating the size of the area you need to be cooled. If you know the square footage of your home, the pros can use this number. If you don’t, or if you’re only cooling part of your home, calculate room size as shown below for window air conditioners and add the rooms together. Once you’ve got your square footage, your HVAC technician will use an AC sizing chart similar to the one below to estimate how big your unit should be.

Area To Be Cooled (square feet)

Capacity Needed (BTUs per hour)

100 up to 150


150 up to 250


250 up to 300


300 up to 350


350 up to 400


400 up to 450


450 up to 550


550 up to 700


700 up to 1,000


1,000 up to 1,200


1,200 up to 1,400


1,400 up to 1,500


1,500 up to 2,000


2,000 up to 2,500


Information from

Your capacity estimations could be higher if:

  • You have more than two people living in your home.

  • Your home is in full sunlight, with no shade.

  • You own multiple appliances that give off heat.

  • You have many or large windows and doors that can leak cooled air.


For example, let’s use the average home in Florida with a square footage of about 1,960 square feet. Assuming you have a family of four and your house has no shade, you’ll need a unit that can move about 34,200 BTUs per hour (BTUh) or 2.85 tons. Always round up to ensure your air conditioner has enough power to cool your home.

For the best performance, our AC installation crew can recommend the ideal unit size and type for your home.

Calculating Window Air Conditioner Sizes

Window air conditioners are less energy-efficient than central air, but they’re ideal for cooling apartments, single rooms, dorm rooms, and other living areas where it’s impossible or impractical to install central air.

If you only need to cool one room, they usually save you money since you avoid cooling the entire house just to keep one room cool.

Calculate the square footage of the room(s) you’ll be cooling. For a rectangular room, multiply the length of one side of the room by its width. For a triangular space, calculate length times width, and divide by two. Divide oddly-shaped rooms into squares and rectangles, adding the square footage for the total room size. Then, reference the above AC sizing chart to find the right size air conditioner for your home.

Two Alternatives to Traditional AC Units: Heat Pumps and Mini Splits

  1. Air-exchange heat pumps, which now come with substantial federal rebates/tax credits, can cool your Naples area home by removing heat and humidity and releasing it into the outside air—and they’re more efficient than traditional air conditioners. Heat pump efficiency is also measured in BTUs, so you can use the same AC sizing chart as standard AC units.

  2. Another alternative is a cooling-only ductless split system, ideal for homes without ductwork and much more efficient than portable window AC units. If you also prefer to have heating, most mini splits on the market will also serve as heaters for you from October through April, if needed, and they also come with new federal incentives since mini splits are a type of heat pump.

Call One Hour Air Conditioning & Heating of Naples for Sizing and Installation

If you’re stumped about sizing a new cooling system, call the experts at One Hour Air Conditioning & Heating of Naples. We’ll calculate the perfect cooling system size and professionally install whatever system you choose.

Ready to upgrade? We’re ready to install your perfectly sized air conditioner, heat pump, or ductless mini-split system in your Naples home. Call (239) 237-3360 or book online today.