The HERS Index and What it Means

The Hers Index Graph

The Home Energy Rating System (HERS) Index is a nationally-recognized system for inspecting and calculating a home’s energy performance. The Residential Energy Services Network (RESNET) created the HERS Index and continues to maintain it. As a homeowner or a potential homebuyer, you should know what the HERS Index is and what a HERS score can tell you.


To determine a home’s HERS score, a comprehensive inspection is performed. The inspection relies on diagnostic testing using specialized equipment: duct leakage testers, infrared cameras, combustion analyzers, and other complex-sounding gadgets. The equipment determines certain variables:

  •  The amount and location of air leaks
  •  The amount of leakage from HVAC
  •  The effectiveness of the home’s insulation
  •  Existing or potential combustion safety issues
  •  Energy impact of floors over unconditioned spaces (i.e. garages and cellars)
  •  Energy impact of attics, foundations, and crawlspaces
  •  Window, door, vent, and ductwork performance
  •  The water heating system and thermostat performance


The HERS inspector gathers the data and puts it into an equation that would make your head spin. But if you’re curious, here’s a substantially-simplified version of the math:


If you enjoy puzzles, take a look at the full equation in the HERS Standard Book (Chapter 3, page 3-4).

The collected data is compared against a “reference home:” a design-modeled home the same size and shape as your home—a doppelganger home, so to speak. So the HERS score is always relative to the size, shape, and type of your home.


A HERS score is a measurement. Your home’s HERS score is like your car’s MPG rating. The higher your car’s MPG rating, the more energy-efficient it is. You can tell from the MPG, how many gallons your tank holds, the price of gas, and the mileage you travel per week how much you will spend monthly in gas to operate your vehicle. If you want to spend less per month, you shop for a car with the highest MPG rating. If you want to spend nothing on gas, you buy an electric car.

The HERS score informs you how much energy it takes to power your home and everything in it: heating and cooling, appliances, lighting, water—you get the picture. But unlike an MPG rating, the lower the HERS score, the better.

The U.S. Department of Energy determined that a typical resale home (polite way of saying older home) scores 130 on the HERS Index. A standard new home (built in 2004 or after) typically scores 100. So a home that scores 80 is 20% more efficient than the standard new home, while a home that scores 110 is 10% less efficient. Given the typical utility costs in your area, the size of your home, time spent at home, and the HERS score, you can estimate how much you will spend on energy each month.


Determining a home’s HERS score is a complex process. Only a certified home-energy rater can perform your energy inspection and diagnosis. To become a certified energy rater, an individual must successfully complete training from a RESNET Accredited Rater Training Provider. The course requires an applicant to pass multiple tests and complete specific tasks:

  • Take the HERS Rater training course
  • Take the National HERS Rater Test(s)
  • Pass the RESNET Combustion Simulation Practical Test
  • Pass the RESNET Rater Simulation Test
  • Complete 5 probationary ratings (probationary ratings are not considered confirmed ratings) with a Rating Quality Assurance Provider overseen by a RESNET Certified Candidate Field Assessor
    • At least 3 of 5 probationary ratings that must be completed using field verification of all rated features of the home in accordance with ANSI/RESNET/ICC 380-2016
    • At least 3 of 5 probationary ratings must be completed in the presence of a RESNET Certified Field Assessor, one of which must be one-on-one


After an individual completes all courses, tests, and training, he or she is now a RESNET Accredited Rating Provider and may apply for a RTIN (ID number). This means you can trust an accredited rater has gone through extensive, specialized training. But be sure to check your rater’s RTIN in the RESNET Building Registry to ensure he or she is legit. It’s a good rule of thumb to check any professional’s license number, no matter the industry they’re in—just putting that out there because we care about you and your safety.


Now you know what HERS is, how it’s determined, and who determines it, but what can you do with this information? Aha! The point!

A HERS audit gives you a detailed report on your home. Many homeowners don’t realize there are many things that affect a home’s energy performance. An energy audit will tell you where your home is underperforming so you can make changes and/or repairs.

There are many cost-effective measures you can take to make your home more efficient. You may need to spend a little at first, but with the money you save in the long run, it’s well worth the investment. According to the Appraisal Journal, for every $1 DECREASE in annual energy costs the market value of your home INCREASES $20. So for every $100 decrease in energy costs, the value of your home increases by $2000.

An energy audit can also uncover hidden problem that when fixed can improve the comfort of your home and improve the health of your living environment.


If you’re looking to buy a new home, and you want to know if it has a HERS rating, click here and enter the home’s address. If you’re shopping for a home in Florida, check out Brite Homes Florida. Beautifully-designed Brite homes come standard with solar panels, energy-efficient appliances, hybrid water heaters, home-automation technology, and many other energy-saving features.

We offer 5 spacious floorplans and with our concierge-style service, you can rest assured we will make your home-buying experience as smooth and comfortable as possible.

Energy-efficient homes are the future. The consumer demand for energy-efficient homes has driven the price down. You may think you can’t afford a solar-powered home. With rising energy costs, you can’t afford NOT to have one. Brite Homes Florida value-engineers our homes for affordability without skimping on luxury. Come on by and see what we have to offer.

Happy house hunting!