Heat Pump Efficiency

Ask Cool Cat: Buying a New AC–What Size Do I Need?

Hey out there Myrtle Beach, Garden City, Socastee! It’s Cool Cat dropping in to answer some of the hot, burning questions we’ve gotten this summer from my peeps out in the Grand Strand. This first one is a doozy of a question and I bet with this crazy, insane, totally wicked heat, there might be a few of you with the same question as my friend Bryan here.

Dear Cool Cat,
My AC just cannot keep up with this summer’s heat! It’s an older unit that came with my house when I bought it. I’m pretty sure it’s time for a new one. I’ve tried doing some research but I can’t figure out what size I need. Can you help?
Sincerely,
Bryan in Surfside Beach

Well, Bryan in Surfside Beach, you are in luck! While I can’t tell you what size AC unit your home needs, I can tell you how the pros figure that out and get you connected up with some cats in the know. So, Bryan, check it out… the industry pros evaluate a set of criteria called Manual J calculations that are provided by the Air Conditioning Contractors of America. First, beware of anyone who says they can tell you what size you need just based on the square footage of your house–it’s so much more than that.

Manual J calculations do include the square footage of your house but also other elements such as roof color, shade around your house, what direction the house is oriented, measurements of the walls, ceilings and windows. They also look at the number of occupants in the home, what types of heat-generating appliances you have, fireplaces, and what the insulation is like in your walls, attic and crawlspace. They look at what kind of siding you have or the exterior material of your home, the sizes of different rooms and the quality of windows and doors (and the seals around them). If it could impact your comfort, they look at it. When they get done gathering all of this information, they use it to generate your cooling load calculations. Make sure you get a copy of those so you can compare contractors.

This cooling load calculation helps determine how many BTUs (British Thermal Units) your system should be able to put out. If the BTU calculation is between two sizes, go with the bigger size so it can more adequately handle extreme temperatures like we’ve been experiencing this year. And Bryan, of course, you can always call the cats at Carolina Cool for help! They are the pros in the know on this topic and can help you determine exactly what size system you need for your pad.