What U-Factor Means and How to Read the NFRC Label
U-factor measures how much heat escapes through a window. Lower is better, and it is the single number that decides both how the window feels in January and whether it earns a utility rebate. It appears on the white NFRC label stuck to the glass of every new window, alongside solar heat gain coefficient and visible transmittance. In our area the numbers that matter are 0.30 and 0.22, because those are the thresholds the Snohomish PUD and PSE rebate programs are written around.
If you are comparing two bids, this is the number to compare. It is also the number a lot of quotes leave off.
What is on the label
The NFRC label is the sticker on the glass of a new window, published by the National Fenestration Rating Council. It rates the whole window, frame and glass together, which is why it is more useful than a claim about the glass alone. Three ratings on it matter to a homeowner here.
U-factor
How much heat passes through the window. The lower the number, the less heat leaves your house.
This is the rating that matters most here, because our heating season is long and our cooling season is short. Comfort near the glass, lower heating bills and less condensation on the inside surface all come from a lower U-factor.
SHGC, solar heat gain coefficient
How much of the sun’s heat comes through, on a scale from 0 to 1. Lower means less solar heat gets in.
In hot climates a low SHGC is the priority. Here it is a balance. Free solar heat through a south-facing window is welcome in February and less welcome during a hot August week. A moderate number suits most homes here, and the exception is a wall of west-facing glass that bakes on summer afternoons.
VT, visible transmittance
How much visible light comes through, also on a 0 to 1 scale. Higher means a brighter room.
Low-e coatings, which is how modern glass gets a low U-factor, reduce visible light somewhat. On a gray winter day in a north-facing room you notice the difference, so it is worth asking about in dark rooms.
Some labels also carry air leakage and condensation resistance. Both are useful, and both matter less than the U-factor and the quality of the installation. A tight window fitted badly still leaks.
The numbers our two utility programs require
Snohomish County PUD
PUD pays $100 per window when you replace single-pane glass and $50 per window when you replace a double-pane frame, in electrically heated existing homes in Snohomish County. The new windows must be double or triple pane rated U-0.30 or lower.
There is no ENERGY STAR requirement in PUD’s rule. The U-factor is what counts. The one requirement people miss is that the work has to be done by a PUD-registered contractor, and Breeze Free is registered for windows. Full details are on our Snohomish PUD rebate page.
Puget Sound Energy
PSE pays by tier, for homes where PSE electricity or PSE natural gas is the primary heat source:
- $50 per window at a U-factor of 0.23 to 0.30, up to $750. Patio doors qualify at 0.31 to 0.35.
- $100 per window at a U-factor of 0.22 or lower, up to $1,500. Patio doors qualify at 0.30 or lower.
- $200 per window on the Efficiency Boost and manufactured-home tiers, up to $2,000 across 10 openings.
PSE allows 15 window rebates per home over the life of the property, installs must be complete by December 31, 2026, and the application is due within 60 days of installation. See the PSE rebate page for the whole program.
Amounts and eligibility can change. Confirm with the utility before you order, and we go through the current rules with you on the estimate visit.
The federal Section 25C credit that covered windows ended on December 31, 2025. There is no federal window credit for a 2026 installation, so the utility rebate is the incentive that remains.
What the difference between 0.30 and 0.22 costs you
The gap between the two PSE tiers is usually a glass package upgrade: a better low-e coating, argon fill, sometimes a third pane. It adds to the price of each window and pays back twice, in the higher rebate and in lower heat loss for as long as you own the house. Whether it is worth it depends on how many windows you are doing and how long you are staying. We put the U-factor for every unit on the quote so you can see the choice as numbers, and we will tell you when the upgrade does not pencil out.
How to read a quote like an inspector
- Find a U-factor listed for every opening. Not a range for the project, not a claim about the glass. Every window, its own number.
- Check it against your program’s threshold. 0.30 or lower for PUD. 0.30 or 0.22 for the two PSE tiers, and remember that patio doors have their own numbers.
- Confirm the installer is registered if you are on PUD. An unregistered installer means no rebate, no matter how good the window is.
- Ask whether the quoted number is for the whole window or just the glass. Glass-only ratings look better and are not what the utility reads.
- Leave the NFRC stickers on until you have recorded what they say, because that information goes on the rebate application.
What we do
Cory confirms your utility and heat type on the estimate visit, before anything is priced. Your written quote lists each window’s U-factor so you can see which units hit which tier. After installation we hand you the product specs and the invoice the application requires, and on PUD jobs we are the registered installer. You submit it, and PSE applications are due within 60 days.
For the longer explanation of glass packages, coatings and what they do in this climate, see our energy efficient window guide and the rebate hub. For the step-by-step on filing, see how to claim PSE and PUD window rebates.
Questions homeowners ask
What is a good U-factor for windows in Washington?
For rebate purposes, 0.30 or lower meets Snohomish PUD’s requirement and PSE’s lower tier, and 0.22 or lower reaches PSE’s higher tier. Lower is better for comfort as well as for rebates, and the tiers are a reasonable guide to what a good window looks like here.
Is ENERGY STAR required for the PUD rebate?
No. Snohomish PUD requires double or triple pane windows rated U-0.30 or lower, installed by a PUD-registered contractor in an electrically heated existing home. Many qualifying windows carry the ENERGY STAR mark, but it is not part of PUD’s rule.
Where do I find the U-factor on my window?
On the NFRC label, the white sticker applied to the glass of a new window. It is also on your quote if the quote is written properly, and on the product specification sheet we hand you at the end of the job for your rebate application.
Get a quote with the numbers on it
Cory measures every opening, confirms your utility and heat type, and sends a written quote within 48 hours that lists the U-factor for each window. Ask for a free estimate and see exactly which units qualify for which tier.
