Sizing Your A/C System

As the old saying goes, bigger isn’t always better. Of course, smaller isn’t always better, either. To get maximum efficiency and effectiveness out of your air conditioner, you’ll need to make sure it’s properly sized, and there are a number of factors to take into account to determine the proper size.

An air conditioner’s cooling power is measured in British Thermal Units, or BTUs. The more BTUs, the more heat your air conditioner can remove from your home per hour. Proper sizing means finding your home’s exact cooling load in BTU and choosing an air conditioner that’s made to match.

Pitfalls of Improper Sizing

Over the course of a half-century in the HVAC industry, we’ve seen a lot of over-sized air conditioners. Having too much cooling power is anything but a good thing, as it will cause the system to constantly cycle on and off. In addition to wasting electricity, this constant cycling leads to uncomfortable temperature changes as the system constantly overshoots your target temperature. Over time, all that turning on and shutting off can even wear out electrical connections, leading to other maintenance issues. Moreover, constant cycling inhibits moisture removal, increasing humidity levels in the home.

Under-sizing can be an even bigger issue than over-sizing, as your system will struggle to keep up with your home’s needs, leading to inadequate cooling. Over time, the increased wear and tear will shorten the lifespan of your air conditioner and lead to more maintenance problems and early system replacement.

In short, it’s critically important to make sure your air conditioner fits your home’s cooling load.

How to Properly Size

Many homeowners incorrectly assume that their home’s square footage is the only thing that determines the cooling load. To be sure, square footage matters quite a lot; all other things being equal, a bigger home needs a bigger cooling system. All other things are never equal, though, and factors like the number of windows, the amount of sunlight that reaches the home, insulation levels in the walls and ceiling, air leaks and load-generating appliances can all increase or decrease your home’s cooling needs.

Once you’ve assessed your home’s circumstances, one of our experienced home comfort advisers will work out the calculation procedures for sizing central air conditioners as provided by the Air Conditioning Contractors of America (ACCA) and the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). Usually this involves a simple computer calculation based on these procedures.

A new central air conditioner is a long-term investment in your home, and you’ll need to take steps to make sure it’s a good one. Proper sizing is the first step toward efficient cooling for years to come.