Modern Window Technology
Look for National Fenestration Council Ratings:
- U-factor: Conduction
losses and far infrared (nonsolar) radiation
- Solar Heat Gain Coefficient (SHGC): Transmissivity to the
entire spectrum of sunlight (both visible and near infrared).
- Visible Transmittance (VT): Transmissivity to visible solar spectrum
- Low-E (low emissivity) double-glazed windows. U-value
Transmission" low-E: Large SHGC
Transmission" low-E: High VT, Low SHGC.