Home Energy Rating System (HERS) Explained
HERS is a tool for comparing and certifying houses based on energy use.
Major energy certifications and green rating systems have used the HERS index for energy certification for years.
Now, HERS scores are working their way into building codes. 2015's IECC adds an Energy Rating Index (ERI) compliance path, and builders can choose their own methods for achieving the HERS score specified for their climate zone, which is between 52 and 55.
HERS is a good resale tool for homeowners because it compares homes for affordability. It is now recognized by the appraisal institute for calculating home value, so it can help your customers make better decisions about energy improvements in the course of remodeling their home.
In this episode of WxTV, Jon Shaffer with PowerHouse Integrated Conservation Systems in Bozeman, Montana, explains the process for doing a HERS audit and entering the data into the REM/Rate software. He also shows us how to shave points off the spread.
The HERS index runs from 0 to 100. One hundred represents a house built to the 2003 IECC. Zero represents a net zero house—one that produces as much energy as it consumes.
Most houses built to 2009 IECC are about a HERS 80.
Steps in a HERS audit:
- Measure the interior space.
- Conduct a blower door test to calculate how much energy is wasted through air leaks.
- Document insulation levels in floors, walls, ceilings, and ductwork.
- Document window u-value and solar heat gain coefficient (SHGC).
- Document door R-values and u-factors for glazed doors.
- Document heating system efficiency.
- Document water system efficiency.
- Document appliance efficiency (dishwashers, refrigerators, clothes dryers, etc.).
- Look at the lighting types.
- Inspect insulation in the walls, floors, and ceiling with an infrared camera.
Measurements and test results are entered into a software called Rem/Rate to calculate the HERS score.
How to shave points from your HERS score:
- Replace incandescent light bulbs with CFLs or LEDs. Good for 2-3 points! (Ed's note: Are incandescents even a thing anymore?)
- Insulating the attic can reduce the HERS score 3-15 points, depending on how good it was to begin with.
- Insulate a crawlspace: 2-3 points
- Insulate a rim joist: 3-5 points
- Air seal can lights: 3 points
- Replace the furnace with a 95% efficient one: 5-15 points
Total possible points shaved: 18-44
HERS also accounts for renewable energy, so adding photovoltaics (PV) can shave your score even more.
Other energy audits and certifications:
BPI Audit: A prescriptive report written by a trained home performance professional. Does not include a HERS score.
Energy Star: A checklist that a builder follows to construct an energy efficient home. Uses HERS score as the energy model for certification. Typical score: low 70s.
LEED for Homes: A green rating system that goes way beyond energy considerations, incorporating durability, water use, materials, and site into account. Uses HERS score as the energy model for certification. Typical score: 80 or below.
PHIUS (Passive House Institute US): Because of the strict airtightness requirements of Passive House, these homes typically score in the low 30's before adding renewable energy.
—Thank you Montana Weatherization Center for doing such good work and sharing it with the crowd.