Why specs matter more than brand
Two windows from different manufacturers at the same price point can have dramatically different performance. The specs on the NFRC label are standardized and verified. That label is the only fair way to compare windows across brands.
The key specs explained
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U-Factor
Why it matters: Measures how well the window insulates (heat transfer from inside to outside). Range is typically 0.
Notes:
SHGC (Solar Heat Gain Coefficient)
Why it matters: Measures how much solar heat passes through the glass. Range is 0-1.
Notes:
VT (Visible Transmittance)
Why it matters: Measures how much natural light comes through (0-1). Higher means more daylight.
Notes:
Low-E coating
Why it matters: Low-emissivity coating is a microscopically thin metallic layer on the glass that reflects heat. Passive Low-E reflects interior heat back inside (good for cold climates).
Notes:
Double pane vs triple pane
Why it matters: Double pane is standard and adequate for most climates. Triple pane adds meaningful insulation in very cold climates (Minnesota, Wisconsin, northern New England) at 30-50% higher cost.
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Frame materials
Why it matters: Vinyl: low maintenance, decent insulation, affordable. Fiberglass: best insulation, most dimensionally stable, higher cost.
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Gas fill (argon vs krypton)
Why it matters: Gas fill between panes improves insulation. Argon is standard and adequate.
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Reading the NFRC label
Every certified window has an NFRC label with U-factor, SHGC, VT, and air leakage ratings. Compare windows using this label, not the marketing description. A "premium" window with poor NFRC numbers is not a premium window. A budget-brand window with good NFRC numbers may outperform it.
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