Size, aka Capacity
A synonym for the air conditioner’s cooling capacity, size is measured in British thermal units per hour (Btu/hr.) or in “tons.” One ton of cooling equals 12,000 Btu/hr. For rough sizing guidance, check the Energy Star website. But the best option is to have your contractor do a load calculation based on a recognized method, such as one in Manual J from the ACCA.
It’s important to pick the right AC capacity for the size of your home. A unit that’s too small will struggle to keep your home comfortable. An oversized unit will cost you more to purchase, and (unless it’s a model with a variable-speed compressor) will cycle on and off more often than it should, stressing the components and struggling to control the humidity in your home.
If you’re replacing your central air, you should look into whether you really need the same size system as your old unit or if you can shrink it a bit. Any changes you’ve made to improve your home’s energy efficiency, such as upgrading your windows or adding insulation, can reduce your cooling needs. On the other hand, if you’ve added rooms, you might need more cooling.
This describes how much cooling the unit delivers for each watt of electricity. Efficiency is expressed as the seasonal energy-efficiency rating, or SEER. The higher the SEER, the greater the efficiency. Higher-SEER ACs tend to cost more, but they’ll often pay for themselves over time through lower energy costs. The minimum SEER allowed for a new split system central air conditioner in the U.S. today is 14, which is at least 20 percent more efficient than minimum-efficiency models made even 10 years ago. Systems that meet the Energy Star guidelines for efficiency have a minimum SEER of 15. The most efficient models reach a SEER of 26.
According to our reader survey, quiet operation is the feature that’s the best predictor for an owner’s overall satisfaction with their air conditioner. Manufacturers publish the noise levels for their products across a variety of outdoor temperatures and fan speeds, measured in decibels. A lower rating is better, especially if the AC will be installed near a bedroom window.
Reliability is the second-best predictor for an owner’s overall satisfaction with an air conditioner (tied with how quickly it cools a room, though that has more to do with whether the AC is sized correctly for your home and whether it’s maintained properly). Consumer Reports members can see the predicted reliability ratings for 23 brands of central air conditioners, based on data that members have shared about the AC units they bought and installed in their own homes between 2007 and 2022.