Measuring Energy Efficiency Using the HERS Index
With everything that’s measured, there has to be a benchmark, a starting point. And that’s true for measuring the energy efficiency of a home. Otherwise, how would we know if we’re meeting goals, getting where we want to be, making progress in decreasing overall energy consumption and the related carbon emissions that lead to climate change? And that’s where the HERS (Home Energy Rating System) comes in.
The HERS Index is a scoring system established by RESNET (Residential Energy Services Network), the national standards-making body for energy efficiency ratings and certifications of buildings in the U.S. It’s derived from the RESNET Reference Home, based on the 2006 International Energy Conservation Code.
Homes built to the specs of the RESNET Reference Home score a HERS Index of 100. The lower the HERS score, the more energy efficient it’s deemed to be. Each one-point decrease in the HERS Index equates to a one-percent reduction in energy consumption compared to the Reference Home.Even though the standard is 100, most houses don’t perform that well. In fact, the U.S. Department of Energy has determined that a typical resale home scores 130 on the HERS Index. Remember, the higher the score the worse the energy performance. For example, a home with a HERS Index Score of 70 is 30% more energy efficient than a RESNET Reference Home.A HERS rating of 100 may be code compliant, and yet still require many solar panels to meet the home’s energy needs. That same house with Passive House features could achieve this with one-fourth the solar panels. This makes a home more affordable to build as well as significantly lowers the cost of ownership. Other than the mortgage, heating, cooling and water heating account for the largest costs of homeownership. And a good place to start is knowing how your home or a home you’re planning to buy performs from an energy standpoint.A HERS Report evaluates the energy features of a home and the expected cost of utility bills. It also answers important questions like, “how efficiently is the home operating?” And “where can modifications be made to increase energy savings?” When you’re selling your home, a low HERS Index Score can bring a higher resale price. And when you’re buying, you can anticipate the costs of energy bills and efficiency upgrades.
A certified RESNET Home Energy Rater can assess a home’s energy efficiency, resulting in a relative performance score or HERS Index Score. To arrive at a HERS Index Score, a certified rater does an energy rating on your home and compares the data to a reference home. The software uses a reference home of the same size and shape as the actual home, so your score is always relative to the size, shape and type of your house.The HERS Rater considers many variables when rating a home, including:
- Exterior walls (above and below grade)
- Floors over unconditioned spaces like garages or basements
- Ceilings and roofs
- Attics, foundations and crawlspaces
- Windows and doors, vents and ductwork
- Air leakage in the home
- HVAC system, water heating system and thermostat
- Leakage in the heating and cooling distribution system