What is SEER for a Heat Cool Air Conditioner?

The EPA establishes the minimum SEER rating for new air conditioning units.  That minimum is 13 SEER.  Most consumers will choose a 13 SEER unit because it has the lowest first cost.  In most installations, SEER should be the last consideration when reducing operating cost.  Factors such as ductwork design, location, insulation and installation quality have significantly more effect on energy consumption than unit SEER.

Before we define SEER, let’s discuss EER “Energy Efficiency Ratio”.  EER is the ratio of output cooling in Btu/Hr and the input power in watts W at a given operating point.  EER (Btu/(W*hr)) EER is a snapshot of efficiency at a given time.  Modern AC units would have an EER of 12. Typical EER for residential central cooling unit = 0.875 X SEER

SEER is the theoretical seasonal efficiency for a unit over an entire cooling season under conditions defined by the American Refrigeration Institute (ARI). 

The SEER is calculated using a part-load standardized ARI test. This more closely represents the performance from changing weather conditions and equipment cycling.

SEER is always a higher value than EER for the same equipment.

SEER = [Total Cooling Output Over the Cooling Season] / [Total Electrical Energy Input Over the Cooling Season]

Older air conditioning systems may have a SEER as low as 5 or 6. EPA required a SEER of 10 for years.  The minimum standard for air conditioners and heat pumps beginning in 2006 is 13 Seasonal Energy Efficiency Rating (SEER). 

To achieve the 13 SEER standard requires changes to the equipment. Generally speaking the new efficiency standard was achieved in two ways. Improved compressor technology and increase in the size of the evaporator and condenser coils.

Remember that SEER is based on the performance of a new unit under laboratory conditions.  After a unit is installed and coils get dirty or fouled the Energy Efficiency can change dramatically.  The EER can be measured before and after service to evaluate effectiveness of the service.