One of the most important aspects in your selection of an Air Conditioning System is proper sizing. A properly sized system will not only cool your home but just as importantly, it will remove moisture. A home that maintains low humidity levels will feel much cooler at any given thermostat setting. 

An oversized system will "short-cycle", meaning that it will cycle on and off more frequently. Short cycling will not allow the run time the system needs to maintain proper humidity levels. In addition the system life expectancy is reduced and your operating cost will spiral upward from the frequent on/off power surges. 

So how do you select the proper system size for your home? Here are your options in descending order of most accurate to least accurate. 

1) Download a system sizing program ( available here ) and input all the construction data about your home. This is by far the most effective as all of the guesswork, opinion, and "rules of thumb" are removed. Your system will perform as the manufacturer intended, your power bills will be as low as possible, and your comfort is assured. (Our sizing program is free with any equipment purchase.) 

Software sizing calculations are required by many municipalities across the country when permitting a new construction home. No "best guesses" are allowed when it comes to a professional, code-correct installation. 

2) Have a contractor visit your home and provide an evaluation of the sizing needed. An experienced contractor in your area may be familiar with your home's floor plan and already know the size needed based on previous evaluations and installations. Unfortunately, contractors will not always agree on the proper size for your home because they may use different criteria. If not, ask them what criteria they used in their evaluation. If they are using only square footage in the evaluation there is absolutely no assurance that the recommended system will function properly. 

When a simplistic evaluation is done, normally the contractor will err on the side of equipment over-sizing as this seems safer to them than under-sizing. The real answer, however, is to purchase the proper size system that is neither too large or too small. 

Don't be afraid to ask questions and expect well thought out answers. Use your judgment when determining who really seems the most interested in providing you with straight-forward, valuable information. 

3) If you are replacing an existing system within your home, locate the model number from the outdoor section. Most manufacturers code the system Btu capacity into the model number. 

For example, model CKL24-1 is a 2 ton unit. Why? There are 12,000 Btu's per ton. The number 24 in the model number indicates the unit is 24,000 Btu's, divided by 12,000 Btu's per ton, equals 2 tons. 

24,000 Btu's/12,000 Btu's per ton = 2 tons 

Use the following conversion information to determine your existing system size (use the model number NOT the serial number) 

18 = 1.5 tons 
24 = 2 tons 
30 = 2.5 tons 
36 = 3 tons 
42 = 3.5 tons 
48 = 4 tons 
60 = 5 tons