Understanding Efficiency Ratings

There is a lot of talk about energy efficiency these days. Since your heating and cooling systems are responsible for a large part our your home’s energy use, efficiency is important. You want to make sure you are not wasting money. When it comes to efficiency, there are a few pretty simple rules of thumb.

  1. New units almost always outperform units that are 10 years old or more.
  2. More efficient units cost more upfront, but will pay for themselves over time because your energy bills will be lower.

Energy Efficiency Ratings for HVAC Systems

Understanding the rating methods used and how they apply to you is not difficult. A simple review of these terms can help you to make more informed buying decision. The terms that are used are:

SEER (Seasonal Energy Efficiency Ratio)

SEER stands for Seasonal Energy Efficiency Ratio.  This rating compares electrical power consumption of an air conditioning unit and evaporator. Federal standards call for all air conditioning units and heat pumps installed in the Charlotte metro area to be at least 14 SEER. For SEER, higher numbers are better. We explain a lot more about SEER in our article All About SEER.

EER (Energy Efficiency Ratio)

The EER or Energy Efficiency Ratio is similar to the SEER. However, a SEER takes into account the seasonal changes which will result in an air conditioning unit having to work harder in hotter weather, but not so hard in cooler weather. EER traditionally measures efficiency in window air conditioners, rather than central air conditioning systems. However, EER is the cooling efficiency rating used by Geothermal heat pump manufacturers like WaterFurnace. How does an EER compare to a SEER? The same cooling system would generally have a somewhat lower EER than SEER. For example, a 13 SEER air conditioner would roughly have an 11 EER. It isn’t a perfect comparison, but it does show you that the most efficient geothermal units with EER ratings around 40 are much more efficient than the average air conditioning system.

AFUE (Annual Fuel Utilization Efficiency)

AFUE stand for Annual Fuel Utilization Efficiency and is used to rate the energy consumption of a natural gas furnace. Just like with SEER, higher numbers indicate increased efficiency. As of 2015, all furnaces must have a minimum AFUE rating of 80%. This means that 80% of the gas used becomes heat for the home, while 20% escapes up the vent pipe or is otherwise wasted. AFUE measures only the efficiency of the furnace, not the duct system. Older furnaces with a continuous pilot light may have an AFUE of 56% to 70%. Most gas furnaces installed in the past 20 years would have had to meet the 80% standard.  The Department of Energy is working toward increasing the minimum required efficiency rate to 92% by 2021, but for now the 80% standard remains.

COP (Coefficient of Performance)

This is another measure of heating system performance. The Coefficient of Performance or COP is a different way of measuring how much of the original energy put into the heating system is utilized as heat. Like everything else in the energy efficiency ratings, a higher COP is a better COP. While measuring gas furnace efficiency uses AFUE, COP is more commonly used in geothermal heat pumps.

CFM (Cubic Feet Per Minute)

CFM stand for Cubic Feet Per Minute. The method of measuring air volume for fans and ducts. SEER ratings are based on air volume of 400 CFM per ton of air conditioning. This is more important for air conditioning than it is for heating.

BTU (British Thermal Unit)

BTU stand for British Thermal Unit which is a measurement of cooling or heating capacity. 12,000 BTU’s equal one ton of air conditioning.  As an example, a 4-ton air conditioner would have a capacity of 48,000 BTU’s.

What the Efficiency Ratings Mean

The higher the SEER or AFUE rating, the less power or gas is used. In theory a 14 SEER air conditioning unit would operate at half the cost of a 7 SEER device or unit. The question one must ask though is does the unit actually perform to the SEER rating the manufacturers’ claim? Should you simply find a unit with a high SEER rating and expect dramatic reduction in your power bills for years to come? The answer is sometimes but more often not.

The ratings of the equipment were calculated in a laboratory setting. There were no allowances made for the air duct system, no consideration for the actual installation, or the building in which it is installed. SEER ratings are based on the assumption that the air conditioning system is correctly installed in the home with a properly designed and installed duct system that is capable of delivering the standard 400 CFM per ton air volume.

Systems that are installed to old, deteriorated, and improperly sized ducts do not even come close to delivering the rated system efficiency. Proper installation of ductwork, grilles, refrigerant piping and system startup procedures are essential for a reliable energy efficient operation. These ratings may be a good way to compare manufacturers’ cooling or heating equipment but are not reflective of how the system will actually perform in your home. There is a lot more to consider in the selection of a quality comfort system than SEER and AFUE ratings alone.