How Do I Size an Air Conditioning System for My Home?

Why Proper Sizing Matters

One of the most important parts of selecting an air conditioning system is proper sizing. A correctly sized system not only cools your home, it also removes moisture. A home that holds low humidity feels much cooler at any given thermostat setting. An oversized system will short cycle, meaning it turns on and off more frequently than it should. Short cycling does not give the system the run time it needs to control humidity, and it shortens equipment life while pushing your operating cost upward from frequent on and off power surges. The goal is a system that is neither too large nor too small.

Your Sizing Options

Software Load Calculation

Running a sizing program with all of your home's construction data is by far the most accurate method, because it removes guesswork, opinion, and rules of thumb. Your system performs as the manufacturer intended, your power bills stay as low as possible, and your comfort is assured. Software sizing is required by many municipalities when permitting a new construction home, since no best guesses are allowed for a code correct installation. AC Direct provides a free sizing program with any equipment purchase.

Contractor Evaluation

A contractor can visit your home and recommend a size based on the floor plan and local experience. Contractors do not always agree, since they may use different criteria, so ask what method each one used. If the estimate relies only on square footage, there is no assurance the system will perform properly. A simplistic estimate often errs toward oversizing because that feels safer than undersizing. Do not be afraid to ask questions and expect well thought out answers.

Read Your Existing Model Number

If you are replacing an existing system, find the model number on the outdoor unit. Most manufacturers code the BTU capacity into the model number. There are 12,000 BTU per ton, so a model such as CKL24-1 is a 2 ton unit because the 24 stands for 24,000 BTU, and 24,000 divided by 12,000 equals 2 tons. Use the model number, not the serial number.