HERS Rating: Home Energy Score Explained

A HERS rating measures a home's energy performance on a numeric scale and helps owners, builders, and buyers compare efficiency objectively. Understanding the HERS rating can cut heating and cooling costs, guide retrofit decisions, and qualify a home for incentives. This article explains what a HERS rating is, how the score is calculated, which upgrades move the needle, and practical DIY steps to improve your home's performance.

TL;DR:

• HERS is a numeric home energy index where 100 = a reference new home and 0 = net-zero; lowering your score by 10 points often saves 10–15% on heating/cooling.
• Simple DIY actions like sealing air leaks, adding insulation to key cavities, and tuning HVAC systems can reduce your HERS score by 5–20 points; use a blower door and energy monitor to track gains.
• Get a certified HERS rater (RESNET) for an official score, follow applicable code compliance paths if required, and consider solar + efficiency together to approach a HERS Index near 0.

Related guides: Living Building Challenge: Beyond LEED and How to soundproof walls in multi unit homes.

What is a HERS Rating?

Understanding the Basics

The HERS rating (Home Energy Rating System Index) is an industry-standard metric created and maintained by RESNET to quantify a home's energy performance on a single scale. The index assigns 100 to a typical new home built to present model-code levels; lower numbers mean better efficiency. A HERS Index of 0 represents a net-zero energy home that produces as much energy as it consumes.

This score is used by lenders, real-estate professionals, and incentive programs. Many incentive and certification programs reference HERS targets when awarding rebates or certifications; for background on national efficiency programs and incentives, see the overview from ENERGY STAR.

How HERS Rating is Calculated

A certified HERS rater models the home using RESNET-approved software. The process includes:

• A whole-house blower door test to measure envelope tightness (ACH50).
• Duct leakage testing (if forced-air systems are present).
• Inspection and verification of insulation levels, window U-values and SHGC, and HVAC equipment performance.
• Input of major systems (water heating, lighting, appliances) and on-site measurements.

The rater compares modeled energy use to a reference home of the same size, shape, and climate. Factors that move the index include insulation, windows, air sealing, HVAC efficiency, duct losses, and renewables like solar PV. For practical guidance on energy-saving measures and how upgrades typically affect bills, refer to the Department of Energy's Energy Saver resources (Department of Energy's Energy Saver).

Why HERS Rating Matters for Your Home

Impact on Energy Bills

A HERS score is not only a number on a disclosure form; it maps to real dollars. Industry guidance often estimates that each 10-point improvement in HERS Index corresponds to roughly a 10–15% reduction in heating and cooling energy use, depending on climate and fuel mix. For a typical 2,000 ft² home spending $1,800 per year on heating and cooling, a 20-point improvement could save $360–$540 annually. Over a decade, verified savings can cover a substantial portion of upgrade costs.

Beyond direct savings, lower HERS scores often increase resale value and unlock utility or state rebates that require verified scores. For background on national energy-efficiency initiatives that influence incentives and market recognition, see the EPA's ENERGY STAR program overview (ENERGY STAR overview).

Environmental Benefits

Lower energy consumption equals fewer emissions. A HERS-driven retrofit that reduces site energy can cut a household's carbon footprint by hundreds to thousands of kilograms of CO2 per year, depending on regional grid intensity. Combining efficiency with on-site solar further reduces net operational emissions; for practical considerations when adding PV, see our guide on Adding solar to existing home considerations.

Energy efficiency also improves occupant comfort and indoor air quality when paired with adequate ventilation. That is especially important for airtight retrofits where controlled ventilation avoids moisture or pollutant buildup—see the Ultimate guide to ventilation for small eco homes for balanced ventilation strategies.

How HERS Ratings Work: A Closer Look

Components of the Rating

Several measurable elements feed the HERS calculation:

• Envelope tightness (ACH50): Measured with a blower door. Lower ACH50 reduces heat gain/loss.
• Insulation levels and continuity: Cavity and continuous insulation values affect conductive losses.
• Window performance: U-factor and solar heat gain coefficient (SHGC) determine conductive and solar loads.
• HVAC efficiency and sizing: AFUE, SEER, and HSPF ratings plus proper sizing change operational energy.
• Duct leakage and location: Leaky ducts in unconditioned spaces add large penalties.
• Domestic hot water: Efficiency of water heaters and distribution losses.
• Lighting and plug loads: The fraction of high-efficiency lighting and ENERGY STAR appliances is modeled.
• Renewable generation: On-site PV reduces net energy use and can dramatically lower the final index.

The HERS software runs an annualized energy model based on local climate data and compares it to the reference home. The resulting index reflects total annual energy use for heating, cooling, water heating, and major end-uses.

Common Improvements to Enhance Score

Typical retrofit measures that move the HERS needle include:

• Air sealing: Sealing attic penetrations, rim joists, and foundational gaps. A blower-door-guided air-sealing campaign can drop ACH50 by 20–40% in many homes. For step-by-step sealing approaches, see our Air sealing existing homes DIY guide.
• Insulation upgrades: Adding cavity or continuous insulation to meet R-values appropriate for climate.
• Window replacement or upgrade: Choosing low-U, appropriate SHGC windows for climate—see recommendations in Top 12 energy efficient windows for canadian climate.
• HVAC tune-up or replacement: Correcting oversizing, sealing ducts with mastic or aerosolized sealants, and installing high-efficiency equipment with proper controls.
• Water heating efficiency: Installing heat pump water heaters or reducing distribution losses.
• Lighting and appliances: Switching to LED lighting and ENERGY STAR-rated appliances.
• Adding solar PV: Credits the modeled annual energy generation, significantly lowering the final index; practical steps are in Adding solar to existing home considerations.

Combined envelope, HVAC, and renewables typically yield the largest score reductions. Small, well-targeted steps often offer better cost-effectiveness than full replacements. For deeper retrofit options and mechanical choices, see guidance on heat-pump alternatives such as Ground source heat pumps geothermal explained.

Applying HERS Ratings to Your DIY Projects

Steps to Get Your Home Rated

1. Find a certified HERS rater: HERS raters are trained and certified through RESNET. They handle modeling, testing, and reporting.
2. Pre-assessment: Gather plans, utility bills, and equipment specs. A rater may do a site pre-check to identify likely upgrades.
3. On-site testing: Expect a blower door test, duct leakage test, and visual inspections. Label equipment and provide access to attics and mechanical rooms.
4. Modeling and report: The rater creates a HERS model and issues the HERS Index report and diagnostic data.
5. Follow-up verification: For projects claiming improved scores (new builds or retrofits), a final inspection and retest confirm upgrades.

If code compliance or incentives are the goal, check whether the local jurisdiction accepts HERS paths under the IECC and verify program requirements with your rater and local building department. For practical planning when building or renovating, consider broader project guidance in How to build your own home.

DIY Tips to Improve Your Rating

• Start with diagnostics: Rent or borrow a blower door and infrared camera for a weekend to find leaky spots. Prioritize sealing those openings.
• Target attic and rim-joist insulation: These areas often provide the biggest thermal gains per dollar. Use dense-pack cellulose or spray foam where appropriate.
• Seal and test ducts: Seal visible ducts with mastic and consider professional duct-blaster testing if ducts run through unconditioned space.
• Install efficient thermostats and controls: A properly programmed thermostat reduces runtime without major expense.
• Monitor energy: Use a whole-home energy monitor and follow calibration and setup best practices; see our DIY energy monitor calibration guide for tips.
• Upgrade water heating: In many regions, switching to a heat pump water heater cuts water heating energy by 50–70%.
• Balance ventilation and filtration: After tightening, install or tune mechanical ventilation (ERV/HRV or balanced systems) to maintain indoor air quality; our Ultimate guide to ventilation for small eco homes covers options for compact builds.

Worth noting: some improvements must be verified by a certified rater to count toward an official HERS score. DIY work can still yield big savings; however, for incentive qualification, coordinate with the rater early.

What to watch out for: oversizing HVAC units. A common retrofit mistake is installing a high-capacity furnace or AC without right-sizing, which raises short-cycling and reduces seasonal efficiency.

Here is a short list of tools and tests to prioritize:

• Blower door: Measures ACH50.
• Duct blaster: Checks duct leakage.
• Infrared camera: Finds insulation gaps and thermal bridges.
• Combustion analyzer: Ensures safe combustion appliance operation after sealing.
• Energy monitor: Tracks changes in energy use after upgrades.

Before investing in large equipment, compare upgrade costs, expected HERS score impact, and available rebates to pick the most cost-effective path. For materials and waste-conscious choices during renovations, see tips in our Ultimate guide to recycled materials for DIY homes.

Common Misconceptions About HERS Ratings

Several myths circulate about HERS scores. Clearing them helps avoid wasted effort.

Myth: HERS rating is only for new homes. Fact: HERS ratings apply to new and existing homes. Many retrofit programs require pre- and post-retrofit HERS scores to document savings.

Myth: Getting a HERS rating is prohibitively expensive. Fact: Costs vary by region and project scope. A basic diagnostic rating for an existing home might cost a few hundred dollars; full pre/post testing and modeling can run higher. The value comes from verified savings and eligibility for rebates that often offset the cost. For national context on energy-saving incentives and program support, see the Department of Energy's Energy Saver resources (Energy Saver overview).

Myth: Only big upgrades move the score. Fact: Low-cost measures like targeted air sealing and thermostat control improvements can produce meaningful index reductions. Deep improvements usually require a combination of envelope, mechanical, and renewable changes.

Myth: Appliances don't affect the HERS score. Fact: Lighting and major appliances are modeled and do affect the final index, but envelope and HVAC usually have larger impacts. Replacing incandescent lighting with LEDs and swapping inefficient refrigerators for ENERGY STAR models yields modest but measurable gains.

Myth: Once rated, the score never changes. Fact: A HERS rating reflects the home at the time of testing. Renovations, equipment changes, and added solar will change the score; re-rating is common after major retrofit work.

The Bottom Line

A HERS rating provides a standardized, verifiable measure of home energy performance that helps prioritize upgrades, unlock rebates, and improve comfort. For DIY builders and self-builders, focusing on air sealing, insulation, and proper HVAC/duct work offers the best initial returns; pair efficiency with monitored energy use and certified testing to document progress toward a lower HERS rating. For material choices and local-cost planning during self-builds, see our posts on How to source local materials for DIY homes and Regional costs for DIY eco homes in canada.

Frequently Asked Questions

What is a good HERS score?

For context, a HERS Index of 100 equals a standard new home and lower is better. Scores in the 50–70 range indicate significantly better-than-code efficiency; a score near 0 indicates net-zero energy. What counts as "good" depends on climate and local code; many ENERGY STAR homes target substantial improvements over code levels (ENERGY STAR overview).

How often should I update my HERS rating?

Update the rating when you complete major renovations, add solar PV, replace HVAC or windows, or if you need an updated score for a sale or incentive. Routine re-rating after a significant retrofit (pre/post) is common practice to verify savings and comply with rebate requirements.

Can I do a HERS rating myself?

Only certified RESNET HERS raters can issue official HERS Index scores accepted by programs and lenders. However, homeowners can perform diagnostic testing—like blower-door-guided air sealing, infrared inspections, and energy monitoring—to prepare for a formal rating and prioritize improvements.

How long does the HERS rating process take?

An initial site visit and testing typically take 2–6 hours depending on house size and complexity. Modeling and report generation can add a few days. If a pre/post retrofit sequence is required, schedule timing with the rater so testing occurs at appropriate stages.

Do energy-efficient appliances affect the HERS score?

Yes. Lighting and major appliances are included in the modeled energy use, so upgrading to ENERGY STAR-rated appliances and LEDs lowers annual modeled consumption and can improve the HERS Index, though envelope and HVAC changes usually have larger effects per dollar spent.