Measuring Home Energy Efficiency: The HERS Index

Measuring Home Energy Efficiency Using The HERS IndexAn energy-efficient home not only cuts the cost of high energy bills, but reduces greenhouse gas emissions. Therefore these types of homes are becoming increasingly popular as buyers look for ways to save both money and the environment. But it can be hard to know what makes a home energy-efficient and how to tell if one house is more efficient than another. Fortunately the Residential Energy Services Network, or RESNET, developed the Home Energy Rating System Index, better known as the HERS Index. Introduced in 2006, the HERS Index is the industry standard for rating a home’s efficiency, as originally reported by RESNET in their new educational video.

MRIS, the industry-leading Mid-Atlantic Multiple Listing Service (MLS) has incorporated the HERS Index in both its listings and code jurisdictions. RESNET’s Executive Director, Steve Baden, commented on the issue, “Including the HERS Index Score in the MLS is a significant push to the mainstreaming of the HERS Index Score in the housing market in the Mid-Atlantic region. REALTORS® rely on the MLS to guide potential homebuyers and appraisers to use the service to locate comparable properties. Having this information will make it easier for builders to market their HERS Index Scores and appraisers to calculate the market value of rated homes.”

Government agencies, such as the Department of Energy and the Department of Housing and Urban Development, recognize a HERS Index score as a building code and compliance option and as an official verification of energy performance. But what exactly is the HERS Index?

The HERS Index is an easy to understand approach to measuring energy efficiency, and is used by homebuilders to demonstrate a home’s total efficiency. It does so by assigning a numerical value to a home, or a HERS Index score, based on the overall energy performance of the home. The lower the score, the better the efficiency leading to smaller energy bills. RESNET describes a HERS Index score as being similar to a miles per gallon sticker.

An independent and certified RESNET HERS rater determines the score of a home. The rater performs an energy rating by inspecting and testing the energy features of a home and entering the information into sophisticated HERS rating software. There are many different variables inside and outside of the home that the rater inspects or tests. Some of the variables inside the home included in an energy rating are: vents and ductwork, HVAC systems, the water heating system, the thermostat, the effectiveness of insulation inside walls and ceilings, and floors over unconditioned spaces, like garages or cellars. Some variables outside the home include: exterior walls, windows, doors, and the foundation. Raters use state-of-the-art specialized equipment to test the efficiency, such as: a blower door tester, duct leakage tester, combustion analyzer, and infrared cameras. These tests can determine the efficiency loss and location of air leaks.

Once the rater inputs the data, the software issues a HERS Index score. This score is in comparison to a reference home, or a model home that is approximately the same size and shape of your home, built to 2006 home building standards. So the score given for any home is always relative to a similar sized model home. According to the US Department of Energy a typical resale home has a HERS Index score of 130, and a standard new home is typically given a rating of 100. However, a home can do much better than 100 and worse than 130. In fact, the Index goes from 0 – 150, with zero being the most efficient house possible and 150 being an inefficient house with high energy bills. A home with a score of zero, or a Net Zero Energy home, produces as much energy or more energy (usually from renewable sources such as wind) as it consumes. A score of 150 means a home is 50% less efficient than a standard new home.

The report from the software also identifies ways a home can become more efficient and increase energy savings. Once it identifies those improvements, the software produces a cost/benefit analysis for any recommended improvements and what the return on making those improvements might be.

A high performance building envelope will help to improve the energy efficiency of a home. The building envelope is the barrier between building’s interior climate and the exterior forces. An important aspect of the envelope is the air and moisture membrane. A high performance membrane like DELTA®-VENT SA improves the performance of the building enclosure with increased air-tightness; it also lets vapor within the structure escape via diffusion. A high performance vapor membrane increases air tightness, and therefore energy efficiency, leading to a lower HERS Index score.

A HERS Index score allows homebuyers to compare the energy efficiency between houses and make a better informed purchase. For those selling a home, a low HERS Index score can increase the value of the home and make it more desirable to consumers. A low Index score is beneficial to all because it improves health and comfort, lowers energy costs, and protects the environment by reducing greenhouse gas emissions. Consider getting your house rated today.