HERS or the Home Energy Rating System is the industries benchmarking tool for modeling a home’s energy use. The system is comprised of two parts; an index and a score. The index is linear with two static points; a “0” equates to a net-zero home (one that produces as much electricity as it uses) while a “100” equates to one just built to code (based on 2006 codes). The score is quite simply where that home lands on the index. For example a home with a score of 65 (easily attainable) is 35% more energy efficient than one built just to code minimums. (RESNET’s Interactive HERS Index tool)
 RESNET or the Residential Energy Services Network developed and oversees all aspects of the HERS program related to the rating, program development, training, & quality assurance requirements. The ratings themselves can only be performed by a Certified Home Energy Rater using approved software.This program originally started out back in 1981 when a group of mortgage industry experts set up the National Shelter Industry Energy Advisory Council to establish a way to measure savings and finding a way to credit the energy efficiency of a home into the mortgage loan. From this council the “Energy Rated Homes of America” was formed and is now known as RESNET. |
How it works:
The home energy rating process starts off with an assessment of the building & its components. This information along with any needed performance testing results (Blower door, Duct Leakage, etc…) is compiled and entered into the software program. Once the rater is satisfied that everything was done properly, they then send it to their Provider for a quality assurance review. Once that is completed (generally within a few days) the rating is issued along with any requested reports. Some of the more popular reports include:
- Code compliance & verification
- “Green” building program compliance & verification
- Estimated Energy Usage
- Heating & Cooling size requirements
- Energy consumption of for the big four; Heating, Cooling, Water Heating and Lights & Appliances
- The component view aka where the heating is being lost during the winter & what is impacting the air conditioning load during the summer
| As you can imagine with the new energy codes & verification requirements (which are all part of the HERS score), many homebuilders are embracing the HERS score & reports as a great marketing tool. The most common line – “Smart consumers examine the HERS Index to determine a home’s energy efficiency before buying, much like checking the MPG sticker on a car”There is no reason you can’t utilize the same tactic when you look to sell your home, especially if you have had work done on it. Most if not all MLS systems have undergone a greening process and have a space for HERS scores & other 3rd party “green” certifications. In many locations where this has caught on, the homes with one have either sold quicker &/or at a higher premium than those without one. |
Two types of ratings:
There are two types of ratings; Provisional & Confirmed ratings. A provisional rating is generally done when a builder or architect provides a set of plans to a rater to review before the house is started. It is also commonly used when a homeowner is considering adding an addition, remodeling or having some upgrades done to their home (especially if they will be utilizing an EEM). A confirmed rating is one where all the diagnostic testing has been completed and everything is verified.
 During the provisional stage is when one can play a ton of what if games – what if I changed my windows to… what if I add a layer of foam at X thickness when I reside my home… is it really worth it moving the ducts inside… what if I add in more insulation in the attic… how does these changes impact the size of my HVAC unit… |
 In order to create the scale a reference house is needed & automatically created by the software. It is basically a mirror image of the house being rated (size, shape, orientation to the sun, location) with a few interesting caveats. First it is assigned the code minimums for the area you live in (R13 or 19 walls, R 30 or 54 for the attic, etc…). It is also assigned code minimum appliances like a hot water heater, HVAC system and incandescent lighting. It then utilizes an automatic window allowance of 18% equally distributed (25% are north facing, 25% are…). Finally it applies a standard formula to determine the usage of all the lights, appliances, and what not. This process is very similar to how energy labels are computed for certain appliances like hot water heaters, dishwashers, TV’s, etc…. and your code minimum house has now been established. |
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