HVAC Efficiency Calculator
Air conditioner efficiency is rated several ways, and they connect through exact definitions. This calculator converts an EER rating to its coefficient of performance, then estimates the seasonal cooling cost from your unit's cooling capacity, its SEER, the hours it runs, and your electricity rate. You see the season's energy use in kilowatt-hours and the dollar cost, plus the EER expressed as COP. The conversions are exact unit relationships; only your electricity rate, which is regional, is an input you supply.
HVAC efficiency formula
Seasonal energy (kWh) = capacity * run hours / SEER / 1,000
Seasonal cost = seasonal energy * electricity rate
Average power (watts) = capacity / SEER
COP = EER / 3.412142
SEER divides cooling output by electrical input over a season, so energy used is output times hours divided by SEER. Dividing watt-hours by 1,000 gives kilowatt-hours. The factor 3.412142 converts EER to a unitless COP.
HVAC efficiency context
- EER is measured at a single test condition; SEER averages over a cooling season.
- COP is a unitless ratio of heat moved to energy used.
- Higher SEER lowers seasonal energy use and cost for the same cooling.
- Electricity rates vary by region; use your own utility rate.
- Minimum SEER requirements are set by U.S. Department of Energy standards.
HVAC efficiency: frequently asked questions
What is the difference between SEER, EER, and COP?
EER (energy efficiency ratio) is cooling output in BTU per hour divided by electrical input in watts at a fixed test condition. SEER (seasonal energy efficiency ratio) averages performance over a cooling season. COP (coefficient of performance) is the dimensionless ratio of heat moved to energy used; EER divided by 3.412 gives COP.
How do I estimate seasonal cooling cost from SEER?
Seasonal energy in watt-hours is cooling capacity in BTU/hr times run hours divided by SEER. Dividing by 1,000 gives kilowatt-hours, and multiplying by your electricity rate gives the cost. Higher SEER means less energy and lower cost for the same cooling.
Why is COP equal to EER divided by 3.412?
EER mixes units (BTU/hr over watts), while COP is unitless. Because 1 watt equals 3.412142 BTU/hr, dividing EER by 3.412142 cancels the units and yields the coefficient of performance. This is an exact unit conversion.
What electricity rate should I use?
Use your own rate in dollars per kilowatt-hour from your utility bill, since rates vary by region and plan. It is an editable input, so the cost estimate reflects what you actually pay rather than an assumed national figure.
Are these conversions exact?
The EER to COP conversion and the energy-to-cost arithmetic are exact, using the defined relationship between watts and BTU per hour. SEER is itself a seasonal average rating, so the cost estimate is as accurate as the SEER and run hours you enter.
Official sources
- U.S. Department of Energy: Central Air Conditioning efficiency.
- U.S. Environmental Protection Agency, ENERGY STAR: Central Air Conditioners.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.