ENERGY STAR. LEED for Homes. Builders Challenge. HERS. It's easy to fall into the wrong line of thinking about this. I did it myself when I was new to the HERS rating industry. It's even easier now that RESNET is out there pushing hard for builders to adopt the HERS Index as a marketing tool. I'm talking about what a home energy rating is all about and how it's different from energy efficiency and green building programs.
Basically, a HERS rating is just an evaluation. A home doesn't have to meet any level of air tightness or insulation R-values or ventilation or overall energy efficiency. Any home can get a home energy rating. The worst home you can imagine can get a home energy rating. Its HERS Index might be 400 (a really bad number, by the way) and it'll even have one star. But it can still have a HERS rating.
The standards for home energy ratings don't list performance requirements for homes. They list performance requirements for home energy raters and their providers, who do quality assurance on raters' work. The requirements in the HERS standards include things like:
- All the insulation in a home has to have a grade — I, II, or III — that describes the quality of installation.
- Conditioned volume includes everything inside the conditioned space boundary (i.e., the building envelope).
- To measure duct leakage for ducts in an encapsulated crawl space, the rater needs to make sure the crawl space is at the same pressure as the house.
I bring this up today because of some of the comments in my latest article at Green Building Advisor, the one on energy codes versus energy efficiency programs. I think the commenters probably do understand the difference, but those who aren't as involved as HERS raters or who are new to the industry may not see the difference between a home energy rating and an ENERGY STAR label on a new home.
So, what's the proper answer to a question like, How much air leakage does a home energy rating allow? It doesn't matter! A house can be as leaky as a sieve and still have a home energy rating and a HERS Index. It's an evaluation tool. Nothing more.