S.E.E.R. Explained – Seattle HVAC Service & Repair

With the ever rising cost of oil, gas and electricity, if you are considering replacing your home’s HVAC system, it is essential that you understand the Seasonal Energy Efficiency Rating (SEER) before making your final decision. The experts at Seattle HVAC Service & Repair can help determine the best system for your needs. There are also measures to be taken if you aren’t quite ready for a full replacement just yet.

Calculate S.E.E.R.

The formula for the SEER for an air conditioner, as determined by the Air Conditioning, Heating and Refrigeration Institute is:

Cooling Output (BTU) x total hours of operation ÷ wattage input

Total hours of operation for the season (ie. 8 hrs/day x 125 days in season = 1,000 hrs)

Cooling output (specified by manufacturer) in British Thermal Units (BTU)

Total wattage input is energy consumed for that same period of time for the system

SEER is expressed as BTU/Watt-hour

From the SEER, you can calculate the expected cost to operate the unit per hour. For example, a unit with a SEER = 10, you can easily compute the wattage consumption average:

(BTU/hour) ÷ (SEER BTU/W-hour) = # Watts

From which the average cost to run the air conditioner for one hour can be calculated:

Wattage consumption x cost/kW-hour

As you can see, as the SEER increases, so too does the efficiency of the unit. Additionally, as the SEER increases, the cost to operate decreases.


The Energy Efficiency Rate (EER) of a cooling unit is calculated using a specific outdoor temperature (95°F) and a specific indoor temperature (80°) at 50% relative humidity. The EER is related to the Coefficient Of Performance (COP). The COP has no units, because the ratio between the cooling load and the power to run the cooling unit are both expressed in Watts, which in ration, cancel each other to make the COP unit-less.

The SEER of a cooling unit is calculated at a constant indoor temperature at the air ducts, but unlike the EER, is the average over a range of outside temperatures in a given geographical location. The range of temperatures used in calculating the SEER is  64° F to 104°F; each calculation is determined by measuring the SEER for a specified percentage of time spent at each of eight temperature ranges (bins) of 5°. As such, the SEER is the specific EER as affected by outdoor temperature differences. The resulting SEER is higher than the EER for a given unit:

EER = 0.875 x SEER

The specific formula for calculating EER:

EER = (-0.02 x SEER2 ) + (1.12 x SEER)

Please note: this calculation method is not for use in all climate conditions. The calculated value is for benchmark purposes only.

The COP is a measure of the number of heat energy units removed from an indoor area per unit of work energy needed to run the cooling unit. Both measures are expressed in Watts. As the COP is without a unit of measure, it can be used for any system of measure.

The experts at Seattle HVAC Service & Repair can perform a complete survey of your home’s cooling needs to determine the best cooling unit for your home.