What is ERI and what's it got to do with HERS?
Updated: May 2, 2019
So you'd just gotten the hang of blower door tests and now everyone's talking about the energy rating index (ERI) and you aren't exactly sure what to think? Well we've got you covered.
What is ERI?
At its most basic level, the ERI compares new homes to a "standard" home built to the 2006 code. It's a new code approval path added to the 2015 IECC. The ERI is continued in the 2018 IECC, but the requirements are actually lightened up.
What is the point of ERI?
ERI is meant to give builders and trades workers more flexibility and more freedom.
The idea is pretty straightforward, actually. The thought is that the code can either prescribe a long list of tasks, standards and requirements to make a house meet the IECC standard, or they can give builders a lot more flexibility in how they do things as long as they meet a single, definable, measurable standard.
What does ERI have to do with HERS?
The 2018 IECC specifically identifies RESNET (the certifying board for HERS ratings) as one of the standards and programs to be used. The 2015 doesn't name RESNET by name but the HERS rating system meets all the standards for ERI.
Bottom line: if you're going to go the ERI route, HERS is what you're looking for.
A HERS rating does the exact same thing: comparing your home to a 2006 standard home. Your HERS rater builds a model of the home on the computer, which will tell you what sort of score to expect. You can test different changes to the design, to the products used, etc and see how it will affect the score.
The HERS rater will do a few inspections of the home during the build to make sure the building crew or subcontractors are doing well and meeting the standards. At the tail end there will be a few tests to confirm the score.
It is that easy. The only extra involvement from you, the builder or developer, is working with the rater for the computerized model...and that is the time where you can figure out how to optimize the home, save money, and make sure you score well.
What are my options other than ERI?
The prescriptive method still exists. If you want to still go down the checklist of the IECC and make sure you follow every single step they lay out and meet every standard they wrote, that is 100% still an option for you.
Nothing will really change in how you build or the processes you follow. That is, depending on how you've been scoring on blower door tests and duct blaster tests.
Very few homes we tested in Tennessee in 2018 met the newer standards for airtightness (the standards are the exact same for 2012, 2015 & 2018 IECCs).
So you'll need to get down from the 7 ACH50 that used to be required to 3 ACH50 now. You'll need to add in mechanical ventilation because you are below the 5 ACH requirement set forth by ASHRAE. Your ducts will have to be tighter. And you'll have to add some more insulation.
Beyond that, you're looking at a pretty similar process if you want to keep doing business as usual.
Why would I pick ERI over the prescriptive path?
There are a lot of reasons, but there are three big ones.
ERI will give you more flexibility. The requirement list is a LOT shorter, so you can make a lot more choices and build the way you want to build.
You'll be able to see (ahead of time) how small changes will affect your score, your costs and the home's performance and comfort.
By going the route of ERI, you will have a HERS rating. That gives you a tool to show potential customers how efficient your homes are, to show them the high quality you build to, and possibly even to qualify for certifications like Energy Star or Zero Energy Ready Homes (ZERH) depending on how good the scores are.
That means a better sales price, reduced liability, help marketing, and peace of mind.
After all, there is a reason that big companies like Meritage Homes choose to get a HERS rating done on every house they build...and that was even before ERI was a code compliance option.
Let's bring it home
The ERI is a new pathway towards code compliance that is available under the 2015 IECC and the 2018 IECC. It gives builders more flexibility. And the 2018 standard is actually easier than the 2015 one!
It allows you to see how changes would affect your score and your rating.
Perfect example: one of our greatest partners chose to get HERS ratings on all their homes. Through the energy model, we were able to show them that by simply going from the water heater they had planned on using to a certain tankless one would improve their score by 3 points.
That's a small change that makes a difference, both to them as they try and get a great score, but also to the future owners who want to have the best, comfiest, and most affordable home possible.
If it weren't for the HERS rating, there would have been no way to measure exactly the difference that small, simple, and inexpensive change could make.