What is the Miles Per Gallon Rating of your Home? The HERS Index in Plain English

The green building / high-performance home industry needs a simple, quantifiable way to demonstrate the value of high-performance homes to the typical homeowner. What is needed is a simple miles per gallon (MPG) rating for homes. The good news is that there is a proven way to measure the energy efficiency of homes, but there is a lack of awareness of this rating system. And when the home’s energy efficiency rating is explained, it’s a number with little context for the average consumer.

HERS Index: The Miles Per Gallon Rating for Your House
In 2006, Residential Energy Services Network, more commonly known as RESNET, introduced the HERS Index to measure a home’s energy efficiency. According to RESNET, a home’s HERS index rating determines “how efficiently it’s operating and where you can make modifications for greater energy savings“. The HERS Index ranges from 0 to 150 points.  RESNET goes on to explain:

  • A home with a HERS Index Score of 70 is 30% more energy efficient than a standard new home
  • A home with a HERS Index Score of 130 is 30% less energy efficient than a standard new home

Out of the 113 million existing homes in the U.S., more than 1 million have received a HERS rating since 1995, making it the home energy rating system with the most rated homes in the world. But what does this HERS rating mean to a typical homeowner? Not much, I’d argue. By comparing a HERS rating to the widely understood Miles Per Gallon rating of cars, a home’s energy efficiency is more easily understood.

You’re Driving a Semi Truck!
In the U.S., more than 72% of the building stock is more than 20 years old. Let’s consider these homes the typical “existing homes”, built in an era of cheap energy (the U.S. still has among the cheapest energy rates in the world). At the other extreme, are net-zero houses that produce all the required energy to operate through on-site renewable energy sources such as photovoltaic systems or wind turbines.

Comparison of the HERS index to the miles per gallon (MPG) ratings of autos.

So would you rather be running errands and commuting to work in a semi truck at 6 miles per gallon or driving a Tesla Model S recharged by on-site renewable energy at 95 miles per gallon? Sure, the Tesla Model S is still the green car of choice of the 1%, but driving a Prius Hybrid (a Pretty Good House) is still significantly better than the standard new home, which is the worst home allowed by law.

Unlike the target market of the Tesla Model S–the wealthy 1%–net-zero homes can be cost-effective for all income classes. Habitat for Humanity is building a net-zero community in River Falls, Wisconsin, making “simple, decent and affordable” housing available. These homes are more energy efficient and have lower maintenance costs than the typical new home purchased.

I know which car I’d drive. I know which home I’d live in. How about you?

Many thanks to John Jimenez for inspiring this post.