HERS testing can help explain why a home uses more energy than expected or feels unevenly heated, but it does not measure comfort or predict your exact utility bills. In the United States, a certified HERS rater assesses features such as insulation, air leakage, ducts and heating and cooling equipment, then uses the findings to produce a HERS Index rating. The result gives homeowners a standardized view of modeled energy performance and can help target upgrades. Its value depends on the tests included, the quality of the report and how well recommendations fit the home. If you’re in New Zealand, confirm that a HERS assessment is applicable to your property and local requirements.
A HERS rating combines information about a home’s construction and energy systems with results from inspections or diagnostic tests. The rater may assess insulation levels and coverage, windows and doors, air leakage, ductwork, heating and cooling equipment, water heating and other features included in the rating. The exact scope can vary with the project and the rating requirements, so ask which measurements and inspections are included before booking.
One common diagnostic is a blower-door test. A temporary fan is fitted into an exterior doorway to pressurize or depressurize the house, allowing the rater to measure how readily air leaks through the building envelope. The test provides a measure of overall leakage; it does not, by itself, identify every leak or explain all indoor air quality concerns.
Duct leakage testing may also be part of the assessment. It can help identify air escaping from the heating or cooling distribution system, but it is not the same as checking whether each room receives the right amount of airflow. A HERS rating can reveal energy-related weaknesses without serving as a full HVAC repair, ventilation or indoor air quality assessment.
The HERS Index compares a home’s modeled energy performance with that of a defined reference home under standardized rating assumptions. A score of 100 represents the reference point; a score of 0 represents net-zero modeled energy use under the rating methodology. In general, a lower score indicates better modeled performance relative to that benchmark.
For example, a score of 70 is commonly understood as indicating modeled energy use about 30% below the reference home. It does not mean your bills will be 30% lower than a neighbour’s, or that you’ll save that amount after a particular upgrade. Actual energy costs depend on factors such as weather, energy prices, household size, thermostat settings and time spent at home—conditions a standardized rating cannot fully reproduce.
Use the score as a summary, not as the whole report. The details behind it—test results, assumptions and recommendations—are more useful for identifying what to fix. A lower score also does not automatically mean a home will feel more comfortable: drafts, room-to-room airflow, solar exposure, controls and humidity can affect comfort in ways a single index does not capture.
These services can overlap, but they answer different questions. A HERS assessment is useful when you want a standardized rating. An energy audit may offer a broader investigation of energy use and potential improvements, while a general home inspection is primarily concerned with the home’s overall condition. The scope of an energy audit varies, so check whether it includes diagnostic testing before comparing it with a HERS assessment.
| Service | Main purpose | What it may include | Key limitation |
|---|---|---|---|
| HERS assessment | Rate modeled energy performance against a reference home | Inspections, energy modeling and tests such as blower-door or duct leakage testing, depending on scope | The score is not a forecast of actual bills or a complete comfort diagnosis |
| Home energy audit | Identify energy-waste concerns and possible improvements | A walkthrough, utility-bill review and, depending on the audit, diagnostic tests and recommendations | Depth and methods vary; an audit may not provide a HERS Index score |
| General home inspection | Review visible condition and major components of a property | Visual checks of accessible areas and systems within the inspection scope | It may not include energy modeling or specialized leakage tests |
Choose the service based on the decision you need to make. If you are comparing modeled efficiency or documenting a rating, ask for a HERS assessment. If you mainly want a prioritized list of practical energy improvements, an energy audit may be a better fit. If you are buying or maintaining a home, do not assume that a standard home inspection includes energy testing.
The process is easier to use when you know what the rater will inspect, which tests are planned and what the final report will contain. Before arranging an assessment, confirm that the rater is qualified to provide the HERS rating you need and ask whether the rating is for an existing home, new construction or a specific project.
Preparation instructions depend on the assessment. Follow the rater’s directions rather than changing vents, equipment settings or other parts of the home to influence the test. If a space or system cannot be inspected, ask how that limitation affects the rating and whether further access or testing would change the result.
A useful report should help connect a measured or observed weakness to a possible action. If air leakage is a concern, ask where the building envelope appears to be losing air and whether sealing work could affect ventilation or combustion safety. If duct leakage is reported, find out which sections are implicated and whether the test assessed total leakage, leakage to outside or another measure.
For insulation, check whether the report describes the location and condition of the insulation, not just its presence. Insulation that is missing, uneven or separated from the intended thermal boundary may contribute to heat loss or gain. For heating and cooling equipment, ask whether the finding concerns the equipment itself, its controls, the duct system or the way it serves the rooms. Those are different problems and may require different professionals.
Use the rating to guide questions and compare options, not to assume that the lowest score is the most cost-effective upgrade. A report may identify efficiency opportunities without calculating project costs, payback periods or the disruption involved. Before committing, request a written scope and estimate from a qualified contractor, and check that the proposed work addresses the issue measured in the assessment.
There is no single price that applies to every HERS assessment. The quote can depend on the home’s size and layout, location, accessibility, rating purpose and the tests or report details requested. A new-construction rating and an assessment of an older home may involve different work. Retesting after upgrades may also be priced differently from an initial visit.
Request a written quote that states what is included, whether testing is performed on site, which areas are excluded, what report you will receive and whether follow-up testing costs extra. If you are commissioning the assessment to meet a program, sale or construction requirement, confirm that the rater and rating meet that requirement before work begins.
For homeowners outside the United States, confirm the geographic fit before relying on a HERS score. HERS is a U.S. rating framework; a local assessor may use different standards, terminology or methods. Ask what the assessment measures, how its results relate to local building practices and whether the score can be used for the purpose you have in mind.
It can be useful if you want a standardized view of modeled efficiency or need evidence to help plan upgrades. If your main concern is a particular defect, such as a cold room or a suspected equipment fault, ask whether a targeted energy audit or HVAC diagnostic would provide more relevant answers.
No. The score reflects modeled performance under rating assumptions, not your household’s actual energy use or future bills. Occupancy, weather, energy prices and thermostat habits all affect costs.
No. It measures overall air leakage under test conditions, but the result does not pinpoint every opening. The rater may use the inspection and other diagnostic methods to help identify likely leakage areas.
It may reveal contributing issues such as envelope leakage, insulation gaps or duct problems, depending on the assessment scope. A rating alone may not identify airflow balancing, control or other room-specific causes, so describe the symptom and ask whether additional diagnostics are needed.
That depends on your goal. An assessment before work can help establish a baseline and guide planning; a post-upgrade rating can document the resulting modeled performance if the same type of rating is appropriate. Confirm in advance which tests are needed and whether the post-work report will be comparable.
Before booking HERS testing, define the problem you want to solve and confirm the assessment’s scope. Then use the score together with the underlying test results to choose improvements, rather than treating the rating as a prediction of comfort or bills.
