When buying both heating and cooling units, many people consider the efficiency rating, model number, features and price, but few consider the size. The size of an AC unit is arguably the most important part of an HVAC system — size can optimize performance and energy efficiency. So how do you know what size of unit you should buy for your home?

How the Size of an AC Unit is Measured

First, an air conditioner’s cooling capacity is based on how many British Thermal Units (BTU) it can remove from the air per hour. The larger the unit, the greater the BTU. Units can be as small as one-ton window units and as large as five-ton central air and gas furnace systems.

This doesn’t mean that you should go out and buy the largest unit possible. There is a correct size air conditioner for every home. If you choose an AC that is too large or too small for your home, it can greatly affect your comfort and energy bills.

Why Proper Air Conditioner Sizing is Important

When you buy an oversized air conditioner, you end up wasting money. A larger system will cool your space quickly, causing it to shut off and turn back on again periodically. When home air conditioners constantly turn on and off again they are less efficient, have higher operating costs and their evaporator coil needs to be repaired more frequently.

In comparison, a smaller air conditioner will run constantly to cool the space, leading to higher electrical bills and decreased efficiency. Although it does run constantly, this AC unit may never reach your desired temperature because of its smaller cooling capacity.

Sizing air conditioners to the space is important for energy efficiency and comfort. When you choose the right size air conditioner for your home, your house will be cool and comfortable. Your unit will also use less energy to cool your house, reducing your electric bills.

How to Choose the Right Size AC Unit

A general rule of thumb is that an air conditioner needs 20 BTU per square foot of living space. The 20 BTU to one square foot ratio helps distribute cold air easier.

Square Foot Heating Guide

Find the square footage range that fits best with your house then match it with the cooling power you need:

300 – 400 sq ft → 12,000 – 18,000 BTU
800 – 900 sq ft → 30,00 – 45,000 BTU
1,200 – 1,400 sq ft → 44,000 – 70,000 BTU
2,000 – 2,2000 sq ft → 80,000 – 115,000 BTU

If you have different total square footage you can easily calculate the correct size AC. Multiply the size of your home in square feet by 20 BTU to find the ideal system capacity for your unit.

Things to Consider When Choosing Air Conditioner Sizes

There are many things to consider when looking at cooling options for your house. In addition to the square footage of your home, it is important to consider these factors:

The age and quality of your home’s insulation: If your house is poorly insulated, then it will have trouble staying cold. As a result, your central or window AC unit will have to work harder to keep your house cool.
Your home’s windows: Newer-style windows tend to have additional insulation. This insulation allows them to hold hot and cold air in with ease. If you have older-style windows, you can expect some of your cold air to escape.
The number of floors in your house: Do you have a second floor? Heat rises, and the second story of your home will likely be warmer than your ground level. It could be a good idea to invest in two air conditioners if one floor acts as an oven and the other a freezer!
Ceiling height: Homes with cathedral ceilings will need greater air cooling capacity because of the extra air capacity.

If one or more of these factors play a part in determining what air conditioning unit you should purchase, it may be best to request a Manual J report from professional cooling contractors. They will complete a calculation based on the insulation, ductwork, climate zone, style of windows and heat loss to determine what BTU rating is best for your air conditioning unit.

Find The Best Air Conditioning Unit

Whether you are interested in a window air conditioner or an outdoor unit that connects to your HVAC system, it is important to find the right size unit. Polcomfort Heating & Cooling can help find the right size of unit for your home. Contact us today for more information.

What Size Air Conditioner Do I Need?