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Climate Zone 5
Energy-efficient windows in Spokane
On a Spokane night the number to compare is U-factor. Washington's residential energy code caps vertical windows at 0.30 in this climate zone. A new window can feel better without a guaranteed drop in the bill.
Spokane winters are long enough that the heat leaving through glass matters every night. Summers still produce hot west light. A useful quote names both, and it names them with the NFRC label on the unit, not with a slogan on the glass.
U-factor is the cold-night number
U-factor measures how fast heat moves through the whole window: glass, spacer, and frame. Lower is slower heat loss. Washington's residential energy code, WAC 51-11R-40213 Table R402.1.3, sets the vertical fenestration maximum at 0.30 for Climate Zone 5 and Marine 4. Skylights on that table are 0.50. Spokane is in Climate Zone 5, so the 0.30 cap is the one that applies to ordinary windows. The table treats U-factor as a maximum. A 0.29 window passes that line. A 0.35 window does not.
The same code says replacement windows have to comply with the residential energy code. That duty is written into WAC 51-51-4502 at R4502.5.1. Codes are amended. Ask the contractor which edition the permit is filed under, and ask to see the NFRC temporary label before the crew peels it off.
Low-E, gas, and what a failed seal looks like
A low-emissivity coating and a double pane of glass are how most vinyl units reach a U-factor of 0.30. Argon between the panes is common. The spacer at the edge of the glass matters too, because the edge is where a lot of heat slips through. Triple-pane can go lower than the code cap. It costs more, it is heavier, and it is a reasonable question for a large north window. It is not a rule this site is imposing.
Solar heat gain coefficient is the other label number. In a heating climate, some winter sun through south glass is useful. West glass can still overheat a room in July. There is no single SHGC that is correct for every elevation of a Spokane house.
Moisture or haze between panes means the seal failed and the insulating gap is gone. Cleaning the room-side glass will not fix it. Sometimes the insulated unit can be reglazed. Often the practical quote is a new window. Comfort may improve. This site will not predict your gas or electric bill.
ENERGY STAR is a voluntary label. Its Northern zone criteria change by version and are often tighter than a code maximum. A window can meet Washington's 0.30 cap without carrying that logo. Read the current climate-zone map on energystar.gov if the logo is part of how you want to choose, and still compare U-factor.
Questions about efficiency
Which window number matters in Spokane?
U-factor on the NFRC label. A lower U-factor means heat moves through the whole window more slowly, which is the useful comparison on a cold night. Washington's residential energy code caps vertical fenestration at a U-factor of 0.30 in Climate Zone 5 and Marine 4. Skylights on that table are capped at 0.50.
Will new windows guarantee a lower energy bill?
No. A tighter window with a lower U-factor can make the wall of glass more comfortable. The bill also depends on the rest of the house, how the window is installed, and how you heat. This site does not estimate savings and does not do the installation.
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