SEER vs EER: Which is more Important in Houston, TX?


What is the difference between SEER and EER? And Why did SEER Win out? How Important is EER for AC systems in Houston, TX?

There are two prevailing measures used to measure the energy efficiency of the cooling portion of an HVAC system.  Air Conditioning efficiency is especially important to us in Houston, TX as it seems we use it nearly year round.  The two measures are SEER and EER.

The association that determines the efficiency of systems in the US is AHRI (Air Conditioning and Heating Institute).  This institute is a trade association that represents equipment manufacturers.  

For some reason along the way our industry agreed to measure air conditioning efficiency in two manners instead of just one.  We use SEER and EER to measure Air Conditioning efficiency.  Think of these as MPGs for your air conditioning unit.  There is a problem with this.  Aside from confusing people with two measures these two sytems are not equally created.  One is a better measure, especially for us hotter states like Texas, while the other is seemingly a lesser measure.  Even still SEER,  the 'lesser' measure, has risen to dominate the efficiency vocabulary of our industry.  Why?  Are HVAC contractors as a result not always providing customers with the absolute best product?

The DEFINITION of these two acronyms are as follows.

SEER = Seasonal Energy Efficiency Rating

EER = Energy Efficiency Ratio

These two terms are so similar but their individual words show striking differences in how they are each measured.  Simply put SEER is measured on the overall average efficiency of your system over the course of a year.  During the course of the year external temperatures vary from lower to higher peak summer temperatures(it does not take them a year to measure the efficiency they merely simulate).  On the other hand EER is only measures system efficiency in a high stress environment with an external temperature of 95 degrees.  Since there is less overall load when a unit is measured for SEER it always ends up with a higher number than EER.  For example a system with an efficiency of 13 SEER may have an EER of 10.5.    

Sure EER and SEER may be viewed as related measurements, however, if they are truly one to one then we should go to a single standard instead of two.  However the problem is that they are NOT always equally correlated.  To prove it look at these related RUUD high efficiency models.

The SEER and EER of each system is given side by side.  Compare the three ton to the 5 ton(#3 vs #5 in left column)  The 3 ton and 5 ton have the same stated SEER of 18.  Whereas the larger system has a lower EER.  14 EER compared to 12 EER.  This makes sense since the system has a larger capacity of 5 tons that it would of course use more energy than a 3 ton.  It can cool a larger space.  

AC Repair Contractors and Customers have a problem when we ONLY look at a systems SEER

We CANNOT assume when two air conditioning systems have the same SEER rating that they will have equal efficiency in "high stress" scenarios.  In the case of many southern states a 95 degree day is pretty normal.

Why did SEER win?

Probably because of the language used by the DOE (Department of Energy).  Government standards for newly manufactured equipment have a minimum efficiency of 13 SEER since 2006.  It appears we have a top down issue.  DOE Fact Sheet


Contractors and customers (especially in southern states) should not overlook EER when comparing HVAC systems.  

Energy Star Definitions of SEER and EER

Contact Us at Mission Air Conditioning for AC Repair Houston