About EER

Energy Efficiency Rating is a measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level (usually 95 degrees F).  A higher EER means the system is more efficient.  The term EER is most commonly used when referring to window and unitary air conditioners and heat pumps, as well as water-source and geothermal heat pumps. 

About SEER

Seasonal Energy Efficiency Rating measures how efficiently a residential central cooling system (air conditioner or heat pump) will operate over an entire cooling season, as opposed to a single outdoor temperature.  As with EER, a higher SEER reflects a more efficient cooling system. 

SEER is calculated based on the total amount of cooling (in Btu) the system will provide over the entire season divided by the total number of watt-hours it will consume.

By federal law, every central split cooling system manufactured in the U.S. today must have a seasonal energy efficiency rating of at least 13.0.

About HSPF

Heating Seasonal Performance Factor is the measurement of how efficiently all residential heat pumps will operate in their heating mode over an entire normal heating season.  The higher the HSPF is determined by dividing the total number of Btu of heat produced over the heating season by the total number of watt-hours of electricity that is required to produce that heat.

Note:  When comparing energy systems that use different primary fuel sources with different costs per Btu, it is important that you understand that higher operating efficiency is not necessarily equivalent to better operating economy.  Although an electric heat pump might work with greater efficiency than a gas furnace, it won't necessarily be more economical to run due to the pricing difference between the two fuel sources.

About AFUE

Annual Fuel Utilization Efficiency is the measurement of how efficiently a gas furnace or boiler will operate over an entire heating season.  The AFUE is expressed as a percentage of the amount of energy consumed by the system that is actually converted to useful heat.  For instance, a 90% AFUE means that for every Btu worth of gas used over the heating season, the system will provide 0.9 Btu of heat.  The higher the AFUE, the more efficient the system.

Today, federal law requires most gas furnaces manufactured and sold in the U.S. to have minimum AFUE's of 78%. (Mobile home furnaces and units with capacities under 45,000 Btu are permitted somewhat lower AFUE's.)  Gas furnaces and boilers now on the market have AFUE's as high as 97%.

About R-value

R-value is the measurement of how effectively a material resists the transfer of heat via conduction.  The higher the R-value, the less heat transfer can take place.