RESNET’s Home Energy Rating System (HERS) has been used to rate the energy efficiency of nearly 2.7 million homes. The data on these homes is housed in RESNET’s National Buildings Registry, which offers a wealth of information on the choices builders are making to build energy-efficient homes. This includes the types of mechanical equipment, insulation, windows, lighting, appliances and the use of renewable energy. To understand the data, you also need to have a general understanding of the HERS® Index scale. The scale generally goes from 0 to 100, where a lower score means less energy use. Each one-point increment on the scale is equivalent to a one percent change in energy use. A home that scores a zero on the scale would produce as much energy as it uses annually This post compares data for all single-family HERS® Rated homes in 2019 against a subset of data that looks only at HERS® Rated homes with an index score of 48 or less from the beginning of 2018 through the middle of 2019. This subset of data is further broken down by homes that received a HERS® Index of less than 26 and those that scored between a 26 and 48. Types of Heating Equipment in HERS® Rated Homes The first data point looks at the type of heating equipment found in rated homes. One thing that stands out is the prevalence of heat pumps (air- and ground-source) in homes that scored less than a 26, while fuel-fired furnaces dominate homes scoring between a 26 and 48 and all rated homes in 2019. This data clearly illustrates the preference of electric heating equipment as homes approach net-zero energy. In fact, when taking into account the water heater fuel data in Figure 4, it’s clear that all electric homes dominate in the net zero or near net zero housing market. Ventilation Strategies in HERS® Rated Homes Over the past several years, ventilation has become a hot topic as building codes push builders to reduce the air leakage of their building envelopes. The chart below shows the choices builders are making to meet ventilation requirements. When comparing the most efficient homes (HERS® of <48) against all rated homes in 2019, it’s clear that the more efficient homes are choosing a balanced ventilation strategy more often; while an exhaust only strategy was the most popular when looking at all rated homes last year. The use of the air handler to bring in ventilation air was the second most popular ventilation strategy for all 2019 homes, but it was not very popular among the most efficient homes. One reason could be due to the use of ductless heating and cooling options for these lower load homes. Water Heating Equipment A look at hot water equipment being installed in HERS® rated homes shows that conventional (storage) water heaters were the most popular product choice last year, but instant water heaters are now being installed in nearly one-third of rated homes. When looking at those rated homes that scored less than a HERS® index of 26, it’s nearly a three-way split among the different water heater options. However, when considering the fuel source (Figure 4) for the two categories of the most efficient homes, it’s clear that electric is the preferred choice for the most efficient homes. The Use of On-site Power Production The use of on-site solar photovoltaics has seen a surge, especially as costs continue to drop and the companies offering solar installations increases. The use of solar on HERS® ratings has been increasing steadily over the past several years, but still less than 10% of all rated homes use solar. However, this changes quite significantly when only considering homes with an index score of 48 or less. Twenty-seven percent of homes scoring between a 26 and 48 have on-site solar, while 82 percent of homes scoring less than a 26 had it. The simple fact is that some form of on-site power production is needed for HERS® rated homes to achieve net-zero energy and the most popular and economic choice is solar. Closing Thoughts The national-average HERS® Index score has been decreasing steadily since at least 2013. The average score across the U.S. in 2019 was a 59. This is an indication that builders of HERS® rated homes are consistently improving the energy efficiency of the homes they build each year. In the push to achieve widespread construction of net-zero energy homes, builders must first maximize efficiency, then use renewable energy to offset the remaining energy consumption of the home. The data on HERS® Rated homes with an index score of 48 or less shows that builders of these homes are moving toward all electric homes and using on-site solar to achieve the lowest HERS® scores. Interested in more data on HERS® rated homes? Are you curious about the cooling, heating and hot water equipment efficiencies being used in HERS® rated homes? What about the amount and type of insulation, types of windows, air leakage rates and dozens of other construction features? RESNET’s Suppliers Advisory Board (SAB) drives much of RESNET’s priorities for analyzing HERS® rating data. A key benefit of the SAB is access to HERS® rating data. In fact, SAB members have received detailed data on HERS® rated homes in 23 states, so far. In 2020, RESNET staff will be undertaking two additional data analysis projects on behalf of the SAB. These two projects include the inaugural report on annual HERS® data trends as well as an in-depth look at how builders are achieving net zero energy and net zero ready homes. A third data project will be updating the first 23 states with 2019 data. For more details on this SAB-member benefit and the many other benefits available to SAB members, visit: https://www.resnet.us/about/sab/.
