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Efficiency Rating Information
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AFUE Annual Fuel Utilization Efficiency
COP Coefficient of Performance
EER Energy Efficiency Ratio
SEER Seasonal Energy Efficiency Ratio
HSPF Heating Seasonal Performance Factor


AFUE Annual Fuel Utilization Efficiency        Back to Top

Applies to fuel burning furnaces, boilers and other combustion heating equipment.

The AFUE compares the annual output energy of the system to the annual input of energy. Since the AFUE rating is averaged for an entire year, it takes into consideration variations in operation due to starting, stopping and seasonal differences.

The AFUE is expressed in percent. For example, a natural gas furnace with a 60% AFUE indicates that the system is only 60% efficient with the remaining 40% of unburned fuel lost up the stack.

Since 1992 all furnaces must have an AFUE of no less than 78%.

Furnaces with AFUE ratings exceeding 95% are readily available.

Furnaces manufactured prior to 1985 usually have an AFUE in the 50 to 60% range. By 1990, the typical efficiency had risen to around 80%.

                   AFUE = Annual Energy Output divided by Annual Energy Input

The purchase and installation of a furnace with a high AFUE is no guarantee that it will actually operate at the listed AFUE. An incorrectly sized furnace for the structure and/or a poor installation will degrade the actual operating AFUE. The AFUE listed on any furnace assumes it is correctly matched for the application and is properly installed.

Note: Replacing a typical residential 60% AFUE gas furnace with a 95% AFUE furnace reduces greenhouse gas emissions (Carbon Dioxide) into the atmosphere by approximately 1,500 pounds per year. Higher AFUE furnaces greatly reduce pollution and help prevent global warming.

COP Coefficient of Performance        Back to Top

Is applied to mechanical cooling systems using refrigerants which also includes high, medium and low temperature systems as well as heat pumps.

Is the ratio of how much energy a system uses versus how much energy the system produces.

Is found by dividing the output by the input.

For example, a coefficient of 2.5 indicates that a heat pump produces 2.5 times more heat output in BTuh than its electrical input in BTuh.

                                      COP = Bthu Output divided by Btuh Input
                                                              or
                      COP = Btuh Output divided by (Input Watts times 3.41 btu/watt)

Ground source heat pumps have the highest Coefficient Of Performance, obtaining COPs as high as 5 as of 2004. A COP of 5 indicates that the heat pump is providing five times as much heat output as it consumes in electrical power.

Typical air to air heat pumps have COPs ranging between 2 and 3.5

The COP listed on the system is not the actual operating COP. An incorrectly sized and/or installed system will operate at a lower efficiency than its rating. Proper selection and installation is critical.

A field determined COP after the installation is complete is the only actual guarantee that the systemis performing at its expected efficiency.

EER Energy Efficiency Ratio        Back to Top

Is applied to mechanical cooling systems using refrigerants. This is an older efficiency rating system which has been replaced with SEER.

Is the ratio of the cooling capacity a system provides as compared to its energy input.

Is found by dividing the name plate output by the name plate input.

The EER fails to consider operational factors such as geographical location, seasonal differences and cycling rates.

                                        EER = Btuh Output divided by Input Watts

SEER Seasonal Energy Efficiency Ratio        Back to Top

Is applied to mechanical cooling systems using refrigerants. Also used to compare heat pump efficiency in the cooling cycle.

The SEER rating is found by dividing the output by the input. However, in addition the SEER rating is adjusted to take into consideration seasonal operational variations and system cycling rates. Therefore, the SEER rating is more realistic and has replaced the EER rating.

                                       SEER = Btuh Output divided by Input Watts
                                         (adjusted to reflect operational variables)

Seer ratings for air conditioning equipment prior to 1992 were in the range of 6 to 8 SEER. Systems manufactured between 1992 and 1998 had SEER ratings between 10 and 13 SEER. SEER ratings have risen to as high as 20 SEER as of 2004. The higher the SEER rating the more the energy savings. However, the initial purchase cost is also higher. A careful calculation comparing initial cost to energy savings can determine the most cost effective SEER for a particular application. The current minimum SEER as mandated by the DOE is 10 SEER. As of January 2006, the minimum SEER will increase to 13.

The SEER listed on the system is not the actual operating SEER. An incorrectly sized and/or installed system will operate at a lower efficiency than its rating. Proper selection and installation is critical.

HSPF Heating Seasonal Performance Factor        Back to Top

Applies to the efficiency of heat pumps.

The HSPF is the ratio of the btuh heating output capacity of a heat pump to the energy input. The HSPF only applies to the heating cycle of the heat pump operation.

The HSPF is an adjusted ratio taking into consideration seasonal operational variations and system cycling rates. Therefore, the HSPF is a fairly realistic energy efficiency rating.

                                       HSPF = Btuh Output divided by Btuh Input
                                        (adjusted to reflect operational variables)

The HSPF listed on the heat pump is not the actual operating HSPF. An incorrectly sized and/or installed system will operate at a lower efficiency than its rating. Proper selection and installation is critical.
 Thermal Efficiency (Boilers Only)

Definitions
Thermal efficiency (Et), also known as “boiler efficiency” or “overall efficiency,” is the boiler’s energy output divided by energy input, as defined by ANSI Z21.13. In contrast to combustion efficiency (Ec), Et accounts for radiation and convection losses through the boiler’s shell.

The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) is working, in conjunction with other groups, to develop a seasonal efficiency rating for boilers. This measure will account for varying efficiency at part-load operation. FEMP expects to adopt this rating method in the future once it is developed and sufficient product ratings are available.

a) This Recommendation covers low- and medium-pressure boilers used primarily in
commercial space heating applications. It does not apply to high-pressure boilers
used in industrial processing and cogeneration applications.

b) These “Best Available” efficiencies do not consider condensing boilers, which are
generally more efficient, but are not readily ratable with ANSI Z21.13.
Cost Effectiveness Example
Lifetime energy cost is the sum of the discounted value of annual energy costs based on average usage and an assumed boiler life of 25 years. Future gas price trends and a discount rate of 3.4% are based on Federal guidelines (effective from April 2000 to March 2001).
U. S. Department of Energy





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