How Do I Know What Size Air Conditioner I Need For My House?

Thinking of buying an air conditioner? Of all the things you should consider, size should be at the top of your list. Purchasing an air conditioning unit that’s too large will be a waste of money, while a smaller unit won’t be adequate to supply cool air into your home.

The good news is that determining the proper size of your air conditioning unit doesn’t have to involve guesswork. Here’s how you can make sure you purchase the ideal air conditioner for your house:

Calculating the Size of Your Air Conditioner

The first (and only) step is to determine the required tonnage of your AC unit. The tonnage, measured in BTUs (British Thermal Units), refers to the unit’s ability to cool an area. Typically, air conditioners require 20 BTUs for every square foot.

To calculate the BTU, multiply the length times the width of the room where you’re planning on installing the unit. Then, multiply that number by 20 BTUs. For instance, if the room is 15 feet wide by 10 feet long, that would mean 15 x 10 = 150 square feet. By multiplying 150 by 20 BTUs, the cooling capacity your home would need is 3,000 BTUs.

Keep in mind, however, that certain factors may affect the size of your air conditioner. These include:

• The square footage of your house.
• The location of your house.
• The climate / outdoor temperature.
• The quality of your house’s ductwork and insulation.
• The size and number of windows in the house.
• The number of persons living in the home.
• The number of appliances that produce heat (e.g. portable heaters)

To ensure that you purchase the most energy-efficient unit, Energy Star recommends making the following adjustments:

• Reduce the cooling capacity by 10% if the room is in a shaded area.
• Increase the cooling capacity by 10% if the room is in a sunny area.
• If more than two persons occupy the room, add 600 BTUs for the third, fourth, etc. person.
• If the AC unit will be installed in the kitchen, add 4,000 BTUs

Cheat Sheet for Determining the Best Size AC Unit

Don’t have the time to measure the space? You can ballpark the square footage of your room and follow the recommendations below

• 100 to 300 square feet = 5,000 to 6,000 BTUs
• 250 to 400 square feet = 7,000 to 8,500 BTUs
• 350 to 650 square feet = 9,800 to 12,500 BTUs (best for homes with an open floor plan)

Ask the Pros

Resist the temptation to search for the ‘best 6,000 BTUs air conditioner’ on Google. To ensure that you purchase the adequately sized unit for your home, consider asking your local HVAC technician for assistance. They can help you select an air conditioning unit that’s the proper size and model

Remember, an air conditioner is an expensive investment. It pays to put in the extra effort into making sure that your AC unit meets your needs. Otherwise, you may end up with one that maxes out your electricity bill each month.