AFUE, SEER, and HSPF Ratings Explained

 

SEER (Seasonal Energy Efficiency Ratio)

The Seasonal Energy Efficiency Ratio (SEER) was developed by the Air Conditioning, Heating, and Refrigeration Institute (AHRI) to serve as a national standard for evaluating the performance of air conditioners. At its core, a SEER rating is a comparative number that reflects how much electricity a unit consumes relative to its BTU output. The actual rating is determined by dividing the total cooling output by the total electricity used in a given period of time. A higher SEER rating always identifies a more efficient air conditioner.

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When shopping for a new AC system, the relative efficiency of two models with different SEER ratings can be calculated by subtracting the lower SEER number from the higher SEER number and dividing the difference by the higher SEER number. For example, the difference between a 10 SEER system and a 16 SEER system is six divided by 16. A 16 SEER unit is 38 percent more efficient than a 10 SEER model.

 

Consumers should be aware of the limitations of SEER ratings when determining overall efficiency. It is important to remember that baseline tests are performed at fixed indoor and outdoor temperatures of 82 degrees and 80 degrees respectively with relative humidity of 50 percent. As the outdoor temperature and humidity rise, the efficiency of the unit declines. Manufacturers conduct a variety of tests to establish the performance of their equipment in extreme temperatures. Always check the extended ratings data to ensure the capacity of the unit reflects the typical summer conditions in your area.

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HSPF (Heating Seasonal Performance Factor)

The Heating Seasonal Performance Factor (HSPF) is specific to heat pumps and used to calculate the efficiency of the unit in the heating mode. A higher HSPF rating identfies a more efficient unit. When operating as an air conditioner, heat pumps are evaluated according to their SEER rating.

 

AHRI developed the HSPF rating as a way to measure the average performance of a heat pump over an entire heating season. Since heat pumps transfer energy rather than extracting it through the combustion process, it is important to recognize that overall heat pump efficiency declines as the outdoor temperature drops. HSPF is calculated by dividing the total seasonal BTU output by the amount of energy consumed in an identical time period. Heat pumps are mandated to have a minimum rating of 7.7 HSPF. Since each watt of electricity yields 3.4 BTUs, a heat pump with a 7.7 HSPF rating will deliver 2.25 times the heat relative to the power it uses.

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AFUE (Annual Fuel Utilization Efficiency)

Furnaces, water heaters and boilers are assigned an Annual Fuel Utilization Efficiency (AFUE) rating, which was created by ASHRAE and mandated as a national standard by the Department of Energy.

 

AFUE is a measurement of combustion efficiency and provides a ratio of nominal energy output relative to fuel consumed. Expressed in percentages, an 80 AFUE furnace delivers 80 percent of the fuel it burns in the form of usable heat while exhausting 20 percent as waste gas.

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Modern furnaces are available in efficiencies up to 98 AFUE. Homeowners with older 70 AFUE furnaces can save up to 30 percent on annual heating costs by installing a new unit. Current AFUE standards include a minimum 90 rating for northern states and an 80 rating for southern climates.

 

Applying Ratings to Utility Costs

Ratings are a critical tool for establishing the efficiency of an HVAC unit and determining annual utility cost savings. An HVAC professional can help establish your current power and fuel usage and explain the benefits of installing modern high-efficiency HVAC equipment.