Home builders can learn how to achieve low Home Energy Rating System (HERS) Index scores by looking closer at data points captured in energy modeling software to see what trends emerge.
Cy Kilbourn of Ekotrope analyzed all the homes registered in its database in 2019 and found that the most common HERS Index score was 58, and the majority of scores fell within a standard bell curve ranging between 45 and 80. Keep in mind, the lower the score, the more energy efficient the dwelling is compared to a 2006 code-built home.
One general industry trend confirmed by these data points is that homes with HERS Index scores below 50 tend to have smaller square footages of livable space, and multifamily units generally have lower scores because of this. Efficient building practices and features also play a role:
Heating equipment type:
- Ground source heat pumps dominated the lower score ranges.
- Homes with air source heat pumps ran the gamut on scores overall, but homes that scored between -20 and 5 (which is almost or even better than net zero energy) had mostly air source heat pumps.
- Electric resistance heating (such as baseboards) was only found in houses that scored 75 or higher.
- Homes that had scores between 25 and 70 mostly had traditional furnaces.
Heating and cooling efficiency:
- Houses that ranged in scores on the lower end from 25 to 40 had Seasonal Energy Efficiency Ratios (SEER) of 17-24, while homes that had HERS Index scores of 45 and above had SEERs hovering at about 14.
- For higher HERS scores in the 70-75 range, the Annual Fuel Utilization Efficiency (AFUE) was in the mid-80s, versus AFUEs of 90 and above for more efficient homes with HERS scores below 55.
Mechanical ventilation type (additional ventilation is key for tighter homes):
- Homes with HERS scores of 40 and below almost exclusively have Energy Recovery Ventilators (ERVs) and Heat Recovery Ventilators (HRVs).
- Homes with scores between 40 and 50 are more likely to have exhaust only
- Houses with HERS scores between around 56 and 80 tend to have air cyclers.
Solar photovoltaics (PV):
- On average, the lowest score without PV is in the low 40s.
- Almost 100% of homes that scored 30 and below have solar PV.
Although there might not be a single formula to get the lowest HERS score, the good news is you have options. To increase energy efficiency, you may want to consider selecting heating and cooling equipment that has a high Coefficient of Performance (COP) and a high SEER, integrating mechanical ventilation, and incorporating renewable energy. Combining multiple efficient products and incorporating sound building science principles into early design and planning stages has the potential to make the building more efficient. As always, many of these choices depend on the client, the project’s geographic location, and local and state codes and regulations.
Trends like these can help builders get a sense of how newly constructed homes in the market have scored on the HERS Index based on various factors. Consider learning more about the HERS Index, and also exploring the value of third-party green certifications on your next build.
For more information about NAHB's sustainable and green building programs, contact Program Manager Anna Stern. And to stay current on the high-performance residential building sector, follow NAHB's Sustainability and Green Building team on Twitter.