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Window U-Values
Estimate your whole-window U-value (Uw) using the same area-weighted method behind NFRC and ISO 10077-1 ratings. Enter your frame U-value, IGU center-of-glass U-value, spacer type, and window dimensions to see the combined thermal performance — plus a breakdown of how much of the heat loss comes from the frame, glazing, and spacer edge.
How to use the calculator:
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Enter your frame's U-value and your IGU's center-of-glass U-value.
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Select your spacer type, or enter a custom Ψ-value if you have tested data.
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Enter the window's overall width, height, and frame face width.
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The calculator returns your whole-window U-value and shows the relative contribution of frame, glazing, and spacer edge to total heat loss.
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