HERS – Home Energy Ratings

Sustainably Built offers RESNET accredited home energy ratings (HERS). Home energy ratings provide a standard measurement of a home’s energy efficiency similar to a miles per gallon rating on cars. Ratings are used for both new and existing homes. In new homes, ratings often verify energy performance for the ENERGY STAR homes program, energy efficient mortgages, and energy code compliance.

Homeowners who want to upgrade the home’s energy efficiency can use the energy rating to evaluate and pinpoint specific, cost-effective improvements. For existing homes, homeowners can receive a report, listing cost-effective options for improving the home’s energy rating. An energy rating allows a homebuyer to easily compare the energy performance of the homes being considered.

There are two types of ratings:

  • Projected ratings – Ratings performed prior to the construction of a home, or prior to the installation of energy improvements to an existing home.
  • Confirmed ratings – Ratings completed using data gathered from an on-site inspection, which could include performance testing of the home.

Projected ratings can be done from blueprints before the house is built. Sustainably Built will review the home to identify its energy characteristics, including insulation levels, window efficiency, wall-to-window ratios, the heating and cooling system efficiency, the solar orientation of the home, the water heating system and any renewable energy components. A projected rating will use an estimate of how tight the house will be built as well as of how leaky the ductwork will be. Boulder County and the City of Boulder will require a projected HERS rating in order to receive a building permit.

In order to receive a confirmed rating, Sustainably Built will perform a pre-drywall inspection, to confirm the quality and thoroughness of the insulation installed. We will also carefully inspect the quality of air-sealing to ensure the anticipated air tightness of the house will be achieved.

After the final finishes are installed in the house, we will perform a blower door test to determine how tightly the house was actually built. If there is ductwork installed for heating or cooling, a duct blaster test will also be performed. This will determine how well sealed the ductwork is. The results of these tests will be entered into the original energy model, and a confirmed rating will be generated.

This final rating should be the same or better than the projected rating. However, if insulation was not properly installed, or the building was not properly air sealed, the confirmed rating could be worse than the projected one. Sustainably Built will work closely with the builder to ensure that this is not the case. If the rating required by building code is not reached, it is possible that the Certificate of Occupancy will be denied until the house can reach the required score.

The data we gather is entered into a RESNET accredited computer program and translated into a rating score. An estimate of the home’s energy costs is also provided in the report. Because a rating quantifies the energy performance of a home, the rating score provides an easily understandable means to compare more efficient homes by their relative energy efficiency.


A HERS rating results in a score that is based on national standards produced by RESNET. A HERS index of 100 is what a standard built-to-code new home would score, while a net-zero energy home would score a 0. Older, existing homes may score a higher number than 100, as they were not built to modern-day building codes.