Performance

U-factor, NFRC labels, glazing and climate.

New to the topic? Start with the full guide to European windows and doors.

• U-Factor for Windows: What Is Good and How Europeans Report Uw

  U-factor is whole-window heat flow in Btu/h-ft2-F, lower is better. 1 Btu/h-ft2-F equals 5.678 W/m2K. See ENERGY STAR and IECC limits by zone.

• The NFRC Label: U-Factor, SHGC, VLT, Air Leakage

  The NFRC label rates a whole window or door for U-factor, SHGC, visible transmittance, air leakage and condensation resistance. How it is produced and read.