Deciphering Energy Efficiency Through the HERS Index

Originally published by: Realtor.comApril 13, 2016

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We're all looking for ways to be more efficient—at work, with our money, with our time. We measure how fuel-efficient a car is by calculating the miles per gallon. To measure the energy efficiency of a house, builders and homeowners use a scale called a HERS Index. So what exactly is the HERS Index, and how does it affect your home?

The Home Energy Rating System (HERS) Index was developed by the Residential Energy Services Network, or RESNET, to gauge how energy-efficient a new home is. The HERS Index applies specifically to new construction or down-to-the-foundation renovations of an existing home. To determine how energy-efficient your existing home is, you'll want to get an energy audit.

The HERS Index

A standard new home earns a HERS Index score of 100. Most house scores fall between 0 to 150. The lower the number, the more energy-efficient the home.

The HERS Index measures the energy efficiency of a house.

According to the National Renewable Energy Laboratory, a home with a score of 20 could save you close to $2,000 on your annual energy bills. (Check out the comparisons here.)

What happens during a HERS Index assessment?

The assessments are performed by a certified HERS Rater who visits the home to perform a comprehensive analysis of how well (or poorly) it conserves heat and uses energy. As part of the assessment, the rater will make recommendations on which upgrades should be considered and their relative benefits.

"The energy efficiency of a home can be improved by reducing the air leakage, adding insulation, or upgrading the heating and/or air-conditioning system,” says Jay Best, owner of Green Audit USA in Islandia, NY.

The comprehensive assessment, which typically costs between $1,500 and $3,000, includes:

  • A duct leakage tester
  • Thermographic imaging that pinpoints exactly where energy is escaping
  • A “blower door test,” which uses a fan to test the air infiltration rate of the home and reveal leaks

According to RESNET, a HERS Rater will assess the following:

  • The amount and location of air leaks in the building envelope
  • The amount of leakage from HVAC distribution ducts
  • The effectiveness of insulation inside walls and ceilings
  • The home’s orientation (with north/south exposure being more efficient)
  • The number and kind of windows (double-pane is a plus)
  • Presence of solar panels or other energy generation methods

Why a HERS Index score is important

Builders use the HERS Index score to specify the minimum efficiency of new home construction before a Certificate of Occupancy is issued.

“Not only does the home design have to meet certain criteria, but the HERS Rater has to test the house and perform and document inspections,” Best explains. These inspections during the construction process ensure the house is built as designed and the insulation is installed correctly.

A home with a lower HERS Index score will save energy and money. While some home listings may include HERS information for new constructions, it hasn't been standardized nationwide. You can also check the HERS Index database to see if your home has been rated in the past.

“Savvy consumers and people shopping for a new home should inquire about the HERS score—an efficient house is more comfortable, healthier, and costs less to operate," Best says.