In Fresno, an energy-efficient window is mostly about keeping the sun's heat out. The NFRC label on a window gives the two numbers that matter, and California's energy code sets limits on both. Fresno is in Climate Zone 13. Here is what the numbers mean and what the 2025 code asks for.
What is a U-factor?
A U-factor measures how much heat passes through the whole window, glass and frame together. Lower is better. Under the 2025 California energy code, replacement windows in Climate Zone 13 can have a U-factor of no more than 0.27 if you replace more than 75 square feet of windows, or 0.40 if you replace 75 square feet or less. The number is on the NFRC label.
What is SHGC (solar heat gain coefficient)?
SHGC is the share of the sun's heat that comes through the glass, from 0 to 1. Lower means less heat. In Fresno it is the number that matters most on west and south walls. Under the 2025 code, the limit is 0.23 for replacements over 75 square feet and 0.35 for 75 square feet or less.
What is low-E glass?
Low-E glass has a thin, clear metal coating that reflects heat. Some low-E coatings are made to block the sun's heat in hot climates, and those are the ones that bring SHGC down. The coating is nearly invisible, though some types have a slight tint. Almost every window that meets the California code today has a low-E coating.
Is triple pane better than dual pane in Fresno?
Triple pane lowers the U-factor more than dual pane, but in Fresno the bigger win is usually a low-E coating that cuts solar heat. Triple pane adds weight and cost. National guides price it very differently: Angi and Fixr put triple glass at $1,000 to $4,000, while Modernize lists it below its own double pane, which looks like an error. Compare the U-factor and SHGC on each label instead.
What does argon gas fill do?
Argon is a heavy, harmless gas sealed between the panes in place of air. It slows the heat that moves across the gap, which lowers the U-factor a little. It stays only as long as the seal holds. Once a seal fails and the window fogs, the gas is gone.
What is the NFRC label?
The NFRC label is a sticker on a new window that lists its tested U-factor and SHGC, rated by the National Fenestration Rating Council. California uses NFRC-certified values first. Building inspectors need to see these labels to confirm the windows meet state rules, so leave them on until the inspection is done.
What do Title 24 and Climate Zone 13 mean for my windows?
Title 24, Part 6 is California's energy code, and Fresno is the reference city for Climate Zone 13. The 2025 code applies to any building whose permit is applied for on or after January 1, 2026. For replacement windows, the limits split at 75 square feet:
| Replacement windows (2025 code, Zone 13) | Max U-factor | Max SHGC |
|---|---|---|
| More than 75 sq ft | 0.27 | 0.23 |
| 75 sq ft or less | 0.40 | 0.35 |
Nearby towns may be in the same zone, but we have not confirmed each one, so ask your building department which zone applies to your address.
Which windows help most with summer heat?
West-facing windows help most, then south-facing ones, because they take the afternoon sun when the house is already hot. Replacing those first with low-SHGC glass gives the biggest change in how a room feels. Outside shade, like an awning, a tree or a patio cover, helps even more, because it stops the sun before it hits the glass.
Do new windows block noise?
New dual-pane windows are usually much quieter than old single-pane aluminum sliders, mostly because they seal tightly. For homes near Highway 99, Highway 41 or a rail line, laminated glass or panes of different thickness cut more noise. Ask for the window's sound rating if noise is the main goal.
Is window film a good alternative to new windows?
Window film can cut heat through old glass for less money, but it does not fix leaky frames, failed seals or a slider that will not close. Some films can void a window maker's terms on dual-pane glass, so check first. Film can be a stopgap for one hot room. If the frames are old aluminum, new windows do far more.
Want a price for your own windows? We measure every opening, show you the frame and glass options side by side and give you a written quote per window. Call or text (559) 354-1055.
This is general information about California, Fresno-area and federal rules, not legal or tax advice. For your own home, check with the office named or a qualified professional.