HERS Rating (Solar Context)
A HERS Rating—short for Home Energy Rating System—is a standardized evaluation of a home’s overall energy performance. It measures how efficiently a home uses energy for heating, cooling, ventilation, appliances, and other loads. In the context of solar home retrofits, a HERS Rating identifies how effectively solar can improve a home’s energy profile and how upgrades (such as insulation, HVAC improvements, or airtightness) interact with photovoltaic (PV) generation.
A lower HERS score indicates a more energy-efficient home. When integrated with solar PV upgrades, a HERS Rating helps homeowners, installers, and energy auditors understand how much solar production is needed, how energy consumption will change over time, and what combined improvements provide the best ROI.
The HERS Rating is widely used in energy audits, home performance retrofits, solar financing, and residential building code compliance, making it a core concept for solar professionals offering whole-home energy solutions.
Key Takeaways
- A HERS Rating measures home energy efficiency and is essential for accurate solar retrofit planning.
- Lower HERS scores reduce energy consumption, allowing smaller and more cost-effective solar systems.
- HERS Ratings guide load modeling, ROI calculations, and proposal accuracy.
- Solar + efficiency upgrades produce the strongest long-term value for homeowners.
- Integrating HERS insights into design tools like SurgePV improves both design quality and customer outcomes.
What Is a HERS Rating?
A HERS Rating is a numerical score—from 0 (net-zero home) to 150+ (inefficient home)—that benchmarks a home’s energy use compared to a reference home built to 2006 energy code standards.
In solar retrofits, HERS Ratings help:
- Diagnose energy inefficiencies before installing solar
- Determine realistic load profiles for solar system sizing
- Reveal opportunities for reducing energy consumption before PV installation
- Improve homeowner savings projections and proposal accuracy
A HERS Rating provides a full snapshot of a home’s demand side, which complements solar’s supply side. Using both together allows solar designers to right-size PV systems with greater precision.
Related concepts include Load Analysis, Solar Savings Calculator, and Solar ROI Modeling.
How a HERS Rating Works (Solar Context)
Although the HERS process is broad, its role in solar retrofits follows a clear workflow:
1. Energy Audit and Home Evaluation
A certified rater inspects the home, assessing:
- Insulation levels
- HVAC efficiency
- Window performance
- Air leakage
- Duct losses
- Water heating
- Ventilation
This determines baseline energy consumption.
2. Load Profile Modeling
Energy-use patterns are modeled and categorized into hourly or seasonal load curves.
Solar system design software—including Solar Designing—uses these profiles to size PV systems accurately.
3. Improvement Recommendations
Before installing solar, raters may recommend:
- Air sealing
- Adding insulation
- Upgrading HVAC
- Installing heat pumps
- Replacing inefficient appliances
These improvements reduce total kWh consumption, enabling smaller or more cost-effective PV systems.
4. Solar PV Integration Analysis
The rater evaluates how solar will offset remaining energy loads.
This includes:
- Estimated solar production
- Annual savings
- Net Energy Metering impact
- Time-of-use interaction
- PV system ROI improvements
For shade and irradiance analysis, see Shading Analysis.
5. Final HERS Score With Solar
Homes often receive a post-retrofit HERS score showing efficiency gains achieved by:
- Home upgrades
- Solar installation
A lower number = better efficiency + stronger solar savings.
Types / Variants of HERS Ratings
1. Pre-Retrofit HERS Rating
Evaluates the home before improvements and before solar is installed.
2. Post-Retrofit HERS Rating
Measures the home’s performance after solar installation and energy-efficiency upgrades.
3. HERS Index with Renewables
A specialized scoring method that includes PV production and energy offset.
4. HERS Rating for Code Compliance
Some jurisdictions require a minimum HERS rating for remodels or additions.
How HERS Ratings Are Measured
A HERS Rating incorporates dozens of inputs, including:
Total Annual Energy Use (kWh)
Calculated from appliances, HVAC, and building shell performance.
Modeled Solar Offset (%)
How much solar production reduces grid consumption.
Home Envelope Efficiency
Air leakage, insulation, and duct loss values.
Mechanical System Efficiency
HVAC SEER, AFUE, COP, and appliance ratings.
Renewable Integration Factors
Solar generation, storage behavior, and load shifting.
These inputs result in a numerical score:
- 100 = standard new home (reference)
- 0 = net-zero home
- < 50 = high-performance home
- > 150 = inefficient home
Typical Values / Ranges
Solar often reduces a home's effective HERS score dramatically.
Practical Guidance for Solar Installers & Designers
1. Use HERS Ratings to size solar systems accurately
A lower HERS score means lower energy consumption, which may require fewer panels.
2. Encourage customers to complete efficiency upgrades before going solar
This reduces the size (and cost) of the PV system needed.
3. Integrate HERS insights into proposal tools
Use hourly load data inside proposal workflows such as the Solar Proposal & Sales Hub.
4. Combine HERS data with shading and POA modeling
For precise performance forecasting, use tools like Shadow Analysis and Sun Angle Calculator.
5. Improve customer ROI storytelling using HERS
A better HERS score = lower utility bills = stronger solar value proposition.
6. Use HERS for whole-home retrofit programs
Installers offering solar + heat pumps + insulation benefit from HERS-driven bundling.
Real-World Examples
1. Pre-Retrofit Audit Leading to Optimal Solar Sizing
A home with a HERS score of 128 required a 9 kW system.
After insulation and duct sealing improved the score to 92, only a 6 kW system was needed.
2. Solar + Heat Pump Retrofit
A homeowner replaced an old gas furnace with a heat pump, lowering energy demand.
After solar installation, the HERS score dropped to 45.
3. New Construction Net-Zero Project
A builder used high-efficiency materials to achieve a score of 52.
Adding a 7.5 kW PV system dropped the final rating to 0 (net-zero).
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