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Climate Zones USA: S = Southern; S C=South-Central; N C=North-Centrall; N=Northern; Door ES=Doors are not separated by zones
View climate zones and qualification criteria for windows and doors at the ENERGY STAR website.
U-Factor (or U-Value): The lower the U-factor, the greater a window's resistance to heat flow and the better its insulating value. Units are Btu/(hr•ft2•ºF).
Solar Heat Gain Coefficient (SHGC): total is a unitless number representing the ratio of radiant solar energy passing through/ incident solar radiation. A small SHGC is desirable during summer. This includes the effect of frame and dividers, which have SHGC of almost zero. Shading Coefficient = SHGC / 0.86.
Visible Transmittance (VT): of the total fenestration product system is the transmittance across the visible portion of the solar spectrum where sensitivity to each wavelength is weighted by the eyes response. Vt is expressed as a dimensionless number from 0 (completely opaque) to 1.0 (completely clear). This value is influenced by the glass selection and by the ratio of glazing and frame area. Vtc high number (Ø.65) means nearly clear view, and low Vt total number means tinted view.
Condensation Resistance (CR): measures how well the window resists water build-up. Condensation Resistance is scored on a scale from 0 to 100. The higher the condensation resistance factor, the less build-up the window allows.
Ratings for products with obscured, wired glass and/or stained glass shall be deemed to be equivalent to the ratings for clear glass.