Energy Efficiency Ratio Calculator
Calculate EER and SEER ratings for HVAC equipment to compare energy efficiency.
Results
How to Use This Calculator
Enter the cooling capacity of the air conditioning system in BTU per hour. This value is found on the unit nameplate or in the manufacturer specifications. A typical 3 ton residential unit has a cooling capacity of 36,000 BTU/hr. Next, enter the total electrical power input in watts. This includes the compressor, condenser fan, and indoor blower. For a 3 ton system, total power input might be 3,200 watts at ARI test conditions. The calculator divides the BTU output by the watt input to produce the EER. For the example above, 36,000 / 3200 = 11.25 EER. You can also enter SEER to convert to EER using the approximation EER = SEER x 0.875, or enter EER to convert to SEER. The tool also displays estimated annual energy costs based on your local electricity rate and cooling hours.
Understanding the Concept
Energy Efficiency Ratio (EER) and Seasonal Energy Efficiency Ratio (SEER) are the primary metrics for comparing air conditioning equipment efficiency. EER measures efficiency at a single operating point: 95 degrees F outdoor, 80 degrees F dry bulb indoor, and 50% indoor RH. It represents steady state performance at near peak cooling conditions. SEER measures seasonal efficiency across a range of outdoor temperatures from 65 to 104 degrees F, weighted to represent a typical cooling season. SEER is always higher than EER because it includes part load conditions where equipment runs more efficiently. As of January 2023, the DOE minimum efficiency standard for residential split system air conditioners is SEER2 14.3 in the northern US and SEER2 15.2 in the southern US, tested under AHRI 210/240 with updated test procedures. Higher SEER equipment costs more upfront but saves on electricity over the system's 15 to 20 year lifespan. ASHRAE Standard 90.1 establishes minimum efficiency requirements for commercial equipment.
The Formula Explained
EER is calculated as: EER = Cooling Capacity (BTU/hr) / Total Power Input (Watts). A unit producing 36,000 BTU/hr while consuming 3,000 watts has an EER of 12.0. SEER accounts for seasonal variations and is calculated using weighted test data at multiple outdoor temperatures: SEER = Total Seasonal Cooling Output (BTU) / Total Seasonal Energy Input (Wh). The approximate relationship between SEER and EER is: EER = SEER x 0.875 (or more precisely, EER = 0.9 x SEER minus 0.6, based on AHRI data). COP (Coefficient of Performance) is the SI equivalent: COP = EER / 3.412, where 3.412 BTU equals 1 watt hour. A 12 EER system has a COP of 3.52, meaning it moves 3.52 units of heat energy for every unit of electrical energy consumed. These efficiency metrics are defined in AHRI Standard 210/240.
Frequently Asked Questions
What is a good SEER rating for an air conditioner?
As of 2023, the federal minimum is SEER2 14.3 in the northern US and SEER2 15.2 in the south. A SEER of 16 to 18 is considered high efficiency and offers good return on investment. Units rated SEER 20 and above are ultra high efficiency, typically using variable speed compressors. The best choice depends on your climate, electricity rates, and how many hours per year you cool.
What is the difference between EER and SEER?
EER measures efficiency at one specific test condition (95 degrees F outdoor). SEER measures average efficiency over an entire cooling season with varying outdoor temperatures. SEER is always a higher number because it includes milder conditions where equipment runs more efficiently. EER is more relevant for hot climates where the AC runs at full load frequently. SEER better represents overall seasonal costs.
How do I convert SEER to EER?
The commonly used approximation is EER = SEER x 0.875. A more accurate formula used by AHRI is EER = (0.9 x SEER) minus 0.6. For a SEER 16 unit: EER = (0.9 x 16) minus 0.6 = 13.8. This is an approximation because the actual relationship depends on the specific equipment design and operating characteristics.
What is SEER2 and how is it different from SEER?
SEER2 uses updated test procedures from AHRI 210/240 2023 that include higher external static pressure on the indoor unit, simulating more realistic installed conditions. SEER2 values are approximately 4.7% lower than equivalent SEER values. A system rated SEER 16 would test at approximately SEER2 15.2 under the new procedure. Federal minimum standards are now expressed in SEER2.
Does higher SEER save money on electricity?
Yes. Each point of SEER improvement reduces cooling energy consumption by approximately 7 to 10 percent. Upgrading from SEER 14 to SEER 18 reduces cooling electricity costs by about 22%. Whether the upfront cost premium is worth it depends on local electricity rates, annual cooling hours, and how long you keep the system. In hot climates with high electricity rates, high SEER equipment pays for itself faster.