HERS Rating (Solar)

Answer: A RESNET HERS Index rating compares a home’s modeled energy performance with a defined reference home. A score of 100 represents the reference; zero represents zero net purchased energy under the rating method. Solar PV can affect the result, but the change must be calculated through the applicable rating process. A solar production estimate alone is neither a HERS certificate nor proof of building-code compliance.

What does the HERS Index measure?

RESNET’s glossary defines the HERS Index as relative energy use against a HERS Reference Home, with consistent rating procedures and assumptions. Lower values indicate better relative performance. The scale is not capped at 150, and its reference value is not the average energy use of every newly built home today.

Treat the rating as a modeled assessment with its own scope. A zero result concerns net purchased energy within that method; it does not mean no electricity is imported at any hour, no utility bill, or complete outage independence. Likewise, a target score is not a universal mortgage, incentive or certification qualification.

For a solar project, retain both the underlying building-performance information and the proposed PV configuration. Insulation, windows, air sealing, heating/cooling and other rated features matter independently of solar production. PV generation does not physically improve an inefficient building envelope.

How solar information reaches the rating

Start by asking the responsible rating professional which standard path, software and documentation apply. Provide the PV design assumptions they request: capacity with DC/AC basis, module/inverter configuration, orientation, tilt, shading and the modeled annual/monthly energy outputs with boundaries and input sources.

RESNET’s current standards overview, updated September 3, 2026, distinguishes minimum and voluntary alternative paths and their addenda. It states that the newer listed standards become the mandatory minimum on January 1, 2027, with applicability determined by permit date or the Chapter 3 alternative. Have the rater confirm the actual path for the home rather than applying the newest document title indiscriminately.

The rating model integrates the building and renewable-energy information according to that path. Do not compute an official score by simply subtracting annual PV kWh from all household energy and dividing by a reference total. Fuels, rated end uses and method-specific calculations must be handled by the rating process.

A production sizing example is not a HERS-score formula

A simple energy target can support the initial PV discussion, provided its limited purpose is clear.

Hypothetical planning example: a designer is asked to supply a modeled annual PV output of 6,000 kWh, and assumes a site-specific modeled yield of 1,500 kWh per kW DC for the year. The arithmetic gives 4 kW DC. Ten assumed 400 W modules also total 4 kW DC.

If a different orientation/shading case has an assumed yield of 1,200 kWh per kW DC, the same energy target would require 5 kW DC under this simplified calculation. The numbers are declared assumptions, not regional yield benchmarks, a complete design or a prediction of HERS points. Ask the rater to evaluate the actual configuration in the applicable model; there is no universal “points per kW” conversion.

Distinguish national ratings from California compliance

The term “HERS” has been used in several contexts. California’s CEC November 2023 advisory distinguished national home-energy rating services from the state-specific whole-house rating and labeling program. That dated advisory should not be used as a current list of approved providers.

For the applicable 2025 California Energy Code, the CEC’s 2025 code overview describes the field-verification program as Energy Code Compliance (ECC), formerly HERS. It identifies the January 1, 2026 effective date for permit applications and the use of 2025 compliance software/documents. A national HERS Index and California’s required compliance documents are not interchangeable.

Confirm jurisdiction, permit date, building type, compliance pathway and current local requirements. Do not assume that every new home has the same PV requirement, that a particular HERS score proves Title 24 compliance, or that adding more PV can replace all mandatory efficiency measures.

Coordinate the builder, designer, installer and rater

A floor-plan worksheet can help track candidate PV packages, but it must retain site orientation, shade, equipment and rating revision. Reusing one assumed score across a development does not eliminate each home’s verification obligations. Coordinate inspection timing with the actual program requirements rather than assuming the PV system must be producing at a particular visit.

For sales teams: distinguish estimated solar generation, projected rating and completed rating. Get written program or lender criteria before discussing eligibility or mortgage benefits. Request a current local quote for rating services; there is no reliable universal fee, resale premium or monthly mortgage saving.

Discuss the solar-design handoff with SurgePV and confirm the outputs available for the project. The rating professional remains responsible for the rating calculation and required documents; do not assume accredited HERS software or a certified HERS-compatible export.

Frequently asked questions

How much does solar reduce the HERS Index?

The result depends on the home, PV system and applicable rating method. Have the responsible rater model the proposed design; there is no universal reduction per kilowatt.

Does a zero HERS Index mean zero utility bills?

No. It describes zero net purchased energy under the rating method. Actual use, import/export timing, tariffs and fixed charges can produce a bill.

Is HERS the same as California energy-code compliance?

No. National ratings and California’s compliance processes have distinct scopes. Confirm the required code edition, pathway, documents and qualified participants for the project.

Does a low HERS score automatically qualify for an incentive?

No. Verify the particular program’s current criteria, effective dates and other requirements. A score alone does not guarantee approval or financial terms.