Choosing The Correct Size Air Conditioner For Your Home

When shopping for a new air conditioner, most homeowners are focused on the price tag; however, choosing the right sized unit is equally important in order to ensure that you get the most out of your investment. An air conditioner that is too big or too small for the size of your home will work harder, which will reduce its life span and cost you more to operate. An improperly sized unit will also not maintain the temperature and humidity in your home at optimal levels, so you will not be as comfortable. Understanding the basics of air conditioner sizing will also help you to compare apples to apples as you price various units.

Manual J Load Calculation

The most common method of determining the correct air conditioner size is known as the Manual J Residential Load Calculation. Manual J is a rather complicated formula that takes into consideration a number of factors, including:

  • the number and location of the windows in your home,
  • the size of the rooms in your home,
  • the materials used to build your home, and
  • how well your home is insulated.

Instead of learning this complicated formula used by HVAC professionals, you can arrive at a close approximation using a much simpler formula. By dividing the square footage of your home by 600, you can estimate the required AC tonnage that you will need to cool your home. Be sure not to include your garage or basement in your calculation. The following can serve as a rough guide:

Square Footage of Home/Size of AC Unit

The unique characteristics of your home, such as the age, layout, and orientation, may require you to install a larger or smaller AC unit. For example, a new, energy-efficient home may require a smaller air conditioner than an older home of the same size.

As a general rule, your rough estimate should be within a half ton of the load calculation provided by your HVAC contractor. If the numbers vary by more than a half ton, you should request that the contractor assess the air return to ensure that it is adequate for the amount of cooling capacity. Of course, it never hurts to ask for a second opinion or to request a money-back guarantee in the event that you are not satisfied.

You can also get a basic idea of the appropriate size air conditioner by looking at your existing unit. The unit’s load capacity is incorporated into the model number of the unit. For example, a model number of GCGD18 would indicate that the unit has a maximum capacity of 18,000 British thermal units. There are 12,000 Btu in a ton, which means that the unit has a cooling capacity of 1.5 tons. The following is a handy Btu to ton conversion guide:

Number of Btu/Number of Tons 


Of course, make sure that you are looking at the model number instead of the serial number. If you are unsure, we are happy to assist.

Types of Central Air Conditioners

There are two basic types of central air conditioning systems. The first option is where the entire air conditioning unit is installed outdoors. The second option is known as a split system. With a split system, the compressor and condenser are installed outdoors while the blower and evaporator are installed indoors on the furnace. This allows the furnace blower to deliver the cool air through your existing duct system, which is more economical.

Window Air Conditioners

The process used for sizing window air conditioners is different than for central air conditioning systems. The first step is to determine the square footage of the room to be cooled by multiplying the width of the room by the length of the room. For example, a 12-foot-by-12-foot room would have a square footage of 144 square feet. You can then refer to the following guide to determine the AC capacity that you will need based on the square footage of the room:

Square Footage/Btu Requirement 

150 to 350 sq. ft./5,000 to 8,000 Btu*
351 to 550 sq. ft./8,000 to 12,000 Btu*
551 to 1,050 sq. ft./12,000 to 18,500 Btu*
1,051 to 1,600 sq. ft./18,500 to 25,000 Btu*

* These ranges are broad estimates and are as meant as a rough guideline for homeowners.
Our process for determining the proper size unit is much more in depth & takes a number of other factors into account.

Just as with central air conditioners, certain conditions may alter your cooling needs. For example, a smaller unit may suffice if the room is heavily shaded. You may want to opt for a slightly larger unit if the room receives a lot of direct sunlight, is heavily used, or if it is used for activities that generate a lot of heat, such as the kitchen.

Whether you need routine AC maintenance, an emergency repair, or a new HVAC system, you can trust Swan Heating & Air Conditioning to provide prompt, professional service. Our team of HVAC technicians has more than 40 years of combined experience and is equipped to handle your air conditioning needs no matter how large or small. With Swan, you will always know the exact cost of your service up front, and all of our work is backed by a 100 percent satisfaction guarantee. Call today for more information about our AC repair and installation services.

Posted in