Efficiency ratings: What's in a number?

Efficiency ratings: What’s in a number?

Efficiency is everything when it comes to heating and cooling, so when you’re buying a heating and cooling system, efficiency ratings count!

As a general rule, efficiency compares what you put into a system to what you get out, no matter what system you’re talking about. Efficiency answers the question, “How well does this thing work?”

The most efficient systems take in little, but return a lot. As systems, ductless air-source heat pumps and air conditioners take in energy and return heated or cooled air.

Since these devices run on electricity and electricity can be expensive, the devices with the best efficiency ratings take in less electricity, but return more conditioned air.

A collection of efficiency ratings

The heating and cooling industry uses a collection of efficiency ratings to compare systems.

Some systems have EER ratings. Others have SEER ratings, and still others have CEER ratings. What are all of these xEER ratings, and how do they compare?


The Energy Efficiency Ratio (EER) is the oldest of the efficiency ratings for air conditioners, and has been around for about 40 years.

An EER rating is calculated using a standard outside temperature of 95°F, a standard inside air temperature of 80°F and a relative humidity of 50%. The ratio tells you how well the system will perform under very specific conditions. The trouble with EER is that systems don’t operate in tightly controlled conditions. EER ratings are most commonly seen on labels for small, window air conditioners and in technical specs.


The Seasonal Energy Efficiency Ratio (SEER) was an attempt to correct the flaws in the EER rating. SEER is calculated using a range of temperatures.

It recognizes that performance varies under different operating conditions. Even though a SEER provides a better approximation of a system’s efficiency, it still suffers from the same problem that EER does: test conditions and performance conditions differ in different parts of the country and at different times during the season. The SEER is most commonly seen on labels for larger, home-sized air conditioners. Ductless air-source heat pumps also use SEER efficiency ratings.


The Combined Energy Efficiency Ratio (CEER) is a standard used for window air conditioners and measures the combined efficiency of the unit when it is in standby and when it’s actually cooling a space.

EER, SEER and CEER efficiency ratings (which are numeric), make it easier for consumers to compare one system to another in terms of energy input and cooling output. Generally, the higher the number, the more efficient the device is. These ratings don’t provide highly accurate information about how much it will cost to operate a system in a specific location. A system with a SEER of 25 is more efficient than a system with a SEER of 15, and generally, the SEER-25 device would cost less to operate than a SEER-15 system in the same circumstance.

Another note: it’s not really possible to compare a device with an EER rating to one with a SEER or CEER, because the ratios measure different things. For the comparison to be valid, compare EER to EER, SEER to SEER or CEER to CEER.

If you’d like more information about air-source heat pumps, efficiency ratings and what they mean for your home, please contact us at New England Ductless or call (781) 995-2665 for more information!

Photo Credit: Larry Cole, via FreeImages.com