US Window Energy Rules: ENERGY STAR 7.0, Colorado, 2027 IECC

With the federal tax credit gone, energy performance now matters mostly because the rules require it. Three things shape what you can sell and install: the ENERGY STAR specification, a growing number of state requirements, and the energy code that your local building department enforces.

ENERGY STAR Version 7.0

EPA’s Version 7.0 specification for residential windows, doors and skylights took effect on October 23, 2023. It uses a revised climate zone map, so the label on a product shows different zones from the older one. If you still quote from an older brochure, check that its ENERGY STAR claims are for Version 7.0.

State rules are starting to bite

Colorado’s HB23-1161 took effect on January 1, 2026. Installer summaries say it requires residential windows, doors and skylights sold for installation in homes of up to three stories to be certified to the ENERGY STAR Northern Climate Zone standard, statewide. It applies to products sold or installed after that date and does not require existing windows to be replaced. California sets its own energy code, and a city compliance form for 2026 shows a maximum U-factor of 0.27 for replacement windows.

The 2027 IECC

The next model energy code is the 2027 IECC. According to Window & Door, the residential committee’s changes lower the prescriptive maximum U-factor for vertical fenestration in Climate Zones 0 and 1 from 0.50 to 0.45, in Zone 2 from 0.40 to 0.35, and in Zones 5 and 6 from 0.28 to 0.27. The solar heat gain limit in Zones 0 to 3 drops from 0.25 to 0.23. Publication was expected in fall 2026, and the article expects early adopters to put it into force in 2028. States adopt on their own timetables, and many are on older editions, so the code that applies to a given job depends on the address.

What to do on a job

• Read the NFRC label on every product you quote and put its U-factor and SHGC on the proposal.
• Ask the local building department which energy code edition and amendments it enforces, and whether a replacement-window permit or energy form is required.
• Write the product’s rated performance into the contract, so a later dispute is about a number and not an opinion.

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