Implications of the 2015 IECC Energy Rating Index (ERI)
Understanding the ERI
Like a miles-per-gallon sticker on cars, an ERI allows homebuyers to compare the energy-efficiency (and estimated annual energy costs) of different homes by providing a score for each house, based on a scale of zero to 100. A HERS Rating is the most commonly used and practical Energy Rating Index in the USA.
A home that scores 100 points is about as efficient as a home built to 2006 standards, and a home that scores zero is considered "net zero".
The 2015 EECC provides the required ERI score for each climate zone to ensure that the efficiency of homes built using this path to demonstrate code compliance are at least as efficient as homes using other compliance paths in 2015. It is imperitive that state and local jurisdictions considering adoption of the 2015 IECC not raise the ERI scores.
All Compliance Paths Must be Equal, Which is Why ERI Scores Seem So Low
The ERI Path is different from other compliance paths because it gives builders credit for installing some high-efficiency items not otherwise covered in the code to compensate for decreased efficiency in the building envelope. This is important because while other compliance paths require 2015-specific building envelope components, the ERI path only requires a building envelope that meets the 2009 requirements.
In fact, while the prescriptive and performance paths cannot take high-efficiency HVAC equipment or home appliances into account when determining the overall building efficiency, the ERI does.
A home gets ERI credit (i.e. a lower score) for features such as solar panels, high-efficiency mechanical equipment such as heating, cooling, and water heating, and appliances (refrigerators, dryers, etc).
There is a possibility that these items will be removed and substituted with less efficient features. Consequently, future home owners may be left with a less efficient and more costly home that is built only to 2009 standards. With this in mind, the ERI scores were set to help ensure that the overall building efficiency is not compromised.