How are new AC units rated?

Before most people buy something new, especially for high ticket items, they will look at the ratings and measurements of the product.  For a car someone might look at MPG, or the resolution if they are buying a new television. But how do you compare new air conditioning systems with so many different manufacturers and models?After the type of system and correct size is determined, you can begin to make “apples to apples” comparisons. The first step is to determine how many stages or speeds does the system have.  This is most applicable for the cooling mode if you are in South Texas. A single stage system is the most basic and affordable. It is either on or off and is controlled by the temperature in the home.  A two stage system has a low and high cooling mode. The benefit for this type of system is humidity control, in other words, this system monitors both temperature and humidity to determine what stage to turn on.  There are also five stage and “true” variable speed systems which improve upon the benefits of the two stage system.  Basically, the more stages the better.

You should also become familiar with terms like SEER and EER.  SEER stands for Seasonal Energy Efficiency Ratio, and EER stands for Energy Efficiency Ratio.  There is an independent company that tests the systems under fixed conditions and applies the appropriate rating.  Without getting too deep in the math behind SEER, it is a measurement of how efficiently a system cools over the course of the summer.  So the higher the number the more efficient a system is. EER is a more direct measurement of how efficient a system operates when running at 100%, but less consideration should be given to this rating especially when looking at multi-stage equipment.

SEER and EER are important numbers and also determine utility rebates (utility companies like CPS and GVEC incentivize customers to upgrade their AC systems).  The SEER range starts at 14 and can exceed 20 on some higher end systems. You should use your budget to maximize the efficiency rating and the number of stages, but be sure to have the duct work checked as well.  Installing a 20 SEER variable speed system on a leaky, poorly designed duct system is like putting wooden wheels on a Ferrari.