A home energy rating "HERS Rating" is a formal method of scoring the energy efficiency of a home.  Although sometimes used interchangeably with the term "energy audit," most audits are not conducted to the same rigorous standards as a formal HERS rating.  An HERS rating is recognized by both the federal government and private industry and may be used for IRS tax credits, energy efficient/energy improvement financing and for EnergyStar certification.  Many web-sites allow you to conduct your own home energy audit but only an accredited HERS rater can perform a formal HERS rating.

Testing involves either slightly pressurizing or depressurizing the home and measuring the pressure changes to the home and the air-conditioning/heating ductwork.  This is known as a blower-door test.  Like your lungs inflating a balloon, the equipment either pressurizes the home by blowing air in or depressurizes the home by sucking air out.  From this information it is possible to measure the amount of air leakage occurring in the home.  Air leakage may account for 40% of a home's heating and cooling costs.  The testing method is completely safe and superbly reliable.

Air-leakage by itself is not necessarily a bad thing.  In some circumstances a very "leaky" home is desireable.  In fact, all buildings must have sufficient air leakage or it becomes necessary to install some kind of ventilation system to provide fresh air and remove pollutants.  Very "tight" homes may become unhealthy for the occupants when contaminated by moisture and indoor pollutants such an carbon monoxide and outgassed chemicals such as formaldehyde.  More information on this critical topic is available at http://www.epa.gov/iaq/homes/hip-ventilation.html

Other methods used to determine air leakage include infrared imaging and tracer-gas analysis.  Ultimately though, a blower door test is the most cost effective.

THE HERS INDEX  A critical step to evaluating your home energy efficiency is determining your Home Energy Rating Index.  The Index is based on a comparison to a computer generated reference building located in the same climate zone and that has the same general physical characteristics as your home.  The reference house meets the minimum requirements of the IECC 2004 and is given an Index rating of 100.  Your home Index is determined using pressure diagnostic equipment and a comparison is made between your home and the reference building.  Each one point difference between your home and the reference building represents one percent difference in energy usage.   So:  If your home scores 85 then your home is using 15% less energy than a home that just meets the standards of the IECC 2004 Code.  Conversely, if your home scores 117 then your home is using 17% more energy than the reference building.

THE STAR SYSTEM  We are often asked about the "Star" rating classification.  The star classification system was developed by the government of Australia and adopted by the Energy Star program here in the United States.  The star system was phased-out in 2006 in favor of the HERS Index as a more uniform way of rating the energy performance of a house.  There are, however, some local code enforcement officials that still refer to the star system.  The HERS rating certificate included with each official rating also still includes the star rating.

Take the first step to energy efficiency.