Energy Modeling and the HERS Rating
The performance of a house is decided on the drawings. Modelling is how you find out before it is built rather than after.
Energy modelling takes the actual design — wall assemblies, window specifications, orientation, air-tightness target, equipment efficiency — and predicts how much energy the finished house will use. It is the tool that tells you whether a net zero target is reachable, and what it would cost to reach it.
The HERS Index is the standard way that result gets expressed in the United States.
Why It Works
Decisions get priced before they are built
Modelling shows what a window upgrade or a thicker wall actually buys, so the money goes where it does the most.
The solar array gets sized honestly
You cannot size generation sensibly without a credible consumption figure.
A number that can be verified
A rated home is tested, not just calculated. Blower door and duct leakage results either confirm the model or expose the gap.
What the HERS Index is
HERS stands for Home Energy Rating System. It is a scoring scale where a reference home built to a standard baseline scores 100, and lower is better. A home scoring 70 uses roughly 30 per cent less energy than that reference. A score of 0 means the house produces as much energy as it uses across the year — which is the same thing as net zero.
The rating is produced by a certified third-party rater, not by the builder. That independence is the point of it.
What testing actually involves
Two measurements do most of the work. A blower door test pressurises the house and measures how much air leaks through the envelope. A duct leakage test does the same for the air distribution system, which in a Florida house is often the larger problem of the two.
Both are done on the finished building. A model that has not been confirmed by testing is a prediction; a rating is a measurement.
Where this fits in the build
Modelling belongs at design, before the plans are stamped — that is when changing a wall assembly or a window specification is a conversation rather than a change order. Testing belongs near completion, when the envelope is closed but there is still time to fix what the test finds.
Energy Modeling & HERS Rating FAQs
Is a HERS rating required in Florida?
A home must demonstrate compliance with the Florida Energy Conservation Code, and a HERS-based performance path is one accepted way of doing that. A low score beyond code minimum is a choice rather than a requirement.
What score does a net zero home need?
A HERS Index of 0 is the definition of net zero energy under that scale. Homes built to a very efficient envelope without generation commonly land somewhere in the 40s to 50s before solar is counted.
Who performs the rating?
An independent certified HERS rater. The builder cannot rate their own work, which is what makes the number worth quoting.
Does a better score raise the appraisal or lower the insurance?
That depends on the appraiser, the lender and the carrier, and it is not something a builder can promise. Ask your own lender and insurer what they do with an energy rating before you count on it.
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