These measure the efficiency of air conditioners and heat pumps. The higher the number, the more efficient the system. The simplest example of how they compare is something most all of us understand, MPG or miles per gallon.

SEER - Seasonal Energy Efficiency Ratio
EER - Energy Efficiency Ratio
COP – Coefficient of Performance
HSPF - Heating Seasonal Performance Factor.

When considering a furnace or boiler this is the measure of efficiency.

AFUE – Annual Fuel Utilization Efficiency. A measure of a gas or oil, furnace or boiler in converting fuel to energy, by projecting the average thermal efficiency for a complete heating season. A higher AFUE rating means greater energy efficiency.

Keep in mind these rating factors all relate to the efficiency of HVAC equipment and not the entire system. Another key component of the system are the air ducts. A duct blast test can be performed to determine the amount of air leakage in ducts. More than a 6% leakage is unacceptable by today’s energy standards. When we visit homes built more than 20 years ago we typically find the air ducts leaking at least 10% and too often as much as 30% or more.

When it comes time to replace your HVAC system most contractors are eager to offer a price and rarely ask you how well does the existing system perform. That question is important for two reasons, efficiency and comfort. Installing a high efficiency system on a leaky or improperly designed duct system is like putting a new high performance engine in an old car with a bad transmission. They only work well when the entire system is designed and working properly.

So if you purchase a 20 SEER air conditioner or heat pump and it’s installed on a leaky duct system it may only perform to the level of a 15 SEER system.


I've never had any home contractor leave my house so spotless....thank you!

- Nancy 
Georgetown, Delaware