What Is a HERS Rating and What Score Should a New Orleans Home Hit?
A HERS rating turns a whole house into one number. Builders put it on spec sheets, some listings mention it, and homeowners are usually left guessing whether the figure they have been shown is good.
The scale is easier than it looks once you know what it is measured against. Here is how it works, what actually moves the number in a New Orleans house, and where a HERS rating is the wrong tool for the job.
What the HERS Index is
HERS stands for Home Energy Rating System. It is run by RESNET, the Residential Energy Services Network, and the rating is carried out by a certified HERS Rater.
The rater collects data on the house, its envelope, its windows, its insulation levels, its mechanical systems and its air leakage, then runs it through approved software. The software compares your house against a reference home: a modelled house of the same size and shape, built to the specifications of the 2006 International Energy Conservation Code.
Because the reference home matches your home’s size and shape, the score is not a reward for living in a small house. It is a measure of how the house performs relative to what a 2006 code-built version of the same house would do.
How the scale works
Three anchor points explain the whole index:
| Score | What it represents |
|---|---|
| 100 | A home built to the HERS Reference Home specification, based on the 2006 IECC |
| 130 | Roughly where a typical existing resale home lands |
| 0 | A net zero energy home |
Lower is better. Each one-point drop on the HERS Index corresponds to a one percent reduction in energy consumption compared with the reference home.
So a house scoring 70 uses about 30 percent less energy than the 2006 reference version of itself. A house scoring 130 uses about 30 percent more. If a rater tells you your 1940s Mid-City double came in at 128, that is not a scandal. That is close to normal for existing housing stock, and it tells you there is real room to move.
What score should a New Orleans home aim for?
There is no single published number that a New Orleans home is supposed to hit, and anyone who quotes you one without asking about the house is guessing.
Two honest reference points:
For an existing home, the useful measure is the change rather than the absolute score. A rating taken before work and again afterwards tells you what your money bought, in a unit that transfers to a future buyer. Chasing a specific number on a 90-year-old raised house can mean spending heavily on the last few points while cheaper measures elsewhere are still untouched.
For new construction, the number is set by whichever compliance path the builder chooses. The Louisiana Energy Code includes an Energy Rating Index option as one of its compliance paths, alongside the prescriptive and performance routes. If your builder is using that path, ask them for the exact index target their plan review is being held to, and ask the rater to confirm it against the Louisiana adopted table rather than the national model code. Louisiana amended several figures when it adopted the 2021 code, so the state table is the one that counts.
What actually moves the score in a local house
The rating software responds to the same things that make a house uncomfortable in August:
- Air leakage. The rater runs a blower door test as part of the rating, and the result feeds the model directly. In a hot, humid climate, this is doing double duty, because leaked air carries moisture as well as heat.
- Attic performance. The ceiling plane is the hardest-working surface in a New Orleans home. Depth of insulation matters, and so does whether there is a real air barrier under it.
- Duct leakage. Ducts running through an unconditioned attic lose conditioned air on the way to the room. This is often the single biggest correctable loss in an older local home.
- Windows and orientation. West-facing glass in a Louisiana summer is a meaningful load.
- Equipment efficiency. The age and rating of the air conditioning and water heating systems.
- The floor system. On a raised pier and beam house, the floor is an exterior surface, which is why floor insulation shows up in the model at all.
Improving a score in this housing stock almost always starts with air sealing and the attic, because that is where the largest uncorrected losses sit. Our post on the signs a home is under-insulated covers what that looks like from inside the house.
What happens during a rating
Expect a data collection visit rather than a repair visit. The rater will:
- Measure the house and record the envelope assemblies, window areas and insulation levels.
- Inspect the attic and the crawl space where there is one.
- Run a blower door test to measure air leakage.
- Test duct leakage.
- Record the make, model and efficiency of the heating, cooling and water heating equipment.
- Enter everything into RESNET-approved software and produce the index score.
The rater is documenting the house as it is. That is a different job from diagnosing what to fix, which is worth understanding before you book.
A HERS rating is not an energy audit
This trips up a lot of homeowners, and the two are often sold as if they were interchangeable.
A HERS rating produces a score. It is a standardised, comparable, transferable number, built for benchmarking one house against another and for demonstrating code or programme compliance.
An energy audit produces a plan. A building science-based audit under the ANSI/BPI-1100 standard is built to deliver a prioritised list of recommendations with a cost-benefit analysis, and it looks at health and safety issues such as combustion appliance safety along the way.
If you want to know how your house scores, get a rating. If you want to know what to do next and in what order, get an energy audit. If you are about to spend money on insulation and want the work targeted, the audit is the one that tells you where to put it.
Where a HERS score is genuinely useful
- New construction. It is the currency builders use to demonstrate performance, and it supports the Energy Rating Index compliance path.
- Before and after documentation. A rating on either side of a retrofit converts your spend into a number a future buyer can read.
- Comparing two houses. Because the reference home scales to size and shape, two homes of different sizes can be compared fairly.
Where it is the wrong tool
- Diagnosing a comfort problem. A score does not tell you why the back bedroom is hot.
- Very old, unusual, or heavily modified houses. Modelling assumptions carry more weight when the house departs from standard assemblies, which describes a lot of New Orleans housing.
- Deciding a budget. The index is not a repair estimate and does not rank measures by return.
Frequently asked questions
What is a good HERS Index score?
Lower is better, and the anchor points give you the context. A score of 100 matches a home built to the HERS Reference Home specification based on the 2006 IECC; a typical existing resale home sits around 130, and a net zero home scores 0. Each point below 100 represents roughly one percent less energy use than the reference version of your house. For an existing New Orleans home, the more useful question is how far the score moves after air sealing and attic work.
Who can perform a HERS rating?
A rating has to be carried out by a certified HERS Rater working under RESNET, using RESNET-approved software. The rater collects the house data, runs a blower door test and duct leakage test, and produces the index score. The credential matters, because a score produced outside that framework is not a HERS rating and will not be accepted for programme or code purposes.
Is a HERS rating the same as an energy audit?
No. A HERS rating scores the house on a standardised index so it can be compared with other homes. An energy audit under the ANSI/BPI-1100 standard is diagnostic, and its output is a prioritised list of improvements with a cost-benefit analysis plus health and safety findings. Ratings answer how the house performs. Audits answer what to do about it.
Does adding spray foam improve a HERS score?
It generally helps, because the rating model is fed directly by the blower door result and by insulation levels, and spray foam affects both when applied to the right surface. The size of the improvement depends on where the house is currently losing energy. If the largest loss is duct leakage in the attic, foam on the roof deck addresses part of that picture while leaky duct connections still need sealing. A rating or an audit done first tells you which lever is actually the big one in your house.
Can an older New Orleans home get a good HERS score?
Yes, though the path is different from new construction. Older local homes usually start high because of air leakage through raised floors, balloon-framed walls and unsealed chases, and because ducts often run through hot attics. Those are correctable. The realistic goal for a historic house is a large improvement from where it started rather than a number matched to a new build, since some assemblies cannot be changed without altering the character of the house.
Do I need a HERS rating to sell my house in Louisiana?
No. A HERS rating is voluntary for an existing home. Sellers sometimes commission one because a documented score, especially paired with a before and after comparison, gives a buyer a standardised figure for how the house is modelled to perform. Read it as a comparison against the reference home rather than a forecast of anyone’s utility bill, since actual bills depend on occupancy, thermostat habits and rates. If you have recently insulated or air sealed, a rating is one way to make that work visible in a listing.
Work out which one your house needs
Star Spray Foam works on homes across New Orleans. If you are weighing a rating against an audit and want to talk it through first, get in touch.
Star Spray Foam
5826 Louis XIV St, New Orleans, LA 70124
504-229-6500
Sources
- RESNET, What Is the HERS Index and Understanding the HERS Score: https://www.hersindex.com/hers-index/what-is-the-hers-index/
- RESNET, HERS Raters and the rating process: https://www.resnet.us/raters/hers-raters/
- ANSI/BPI-1100-T-2023 Home Energy Auditing Standard: https://www.bpi.org/__cms/docs/ANSI-BPI-1100-T-2023_Home_Energy_Auditing_Standard_2023-06-06.pdf
- Louisiana Energy Code 2021, Section R401.2.3 compliance paths including the Energy Rating Index option, via UpCodes: https://up.codes/viewer/louisiana/iecc-2021/chapter/RE_4/re-residential-energy-efficiency
