Energy Performance Ratings
Energy efficiency is the most important feature of replacement windows. Here’s how to decode the labels:
R-value measures heat insulation. Higher is better.
U-value measures heat transfer. Lower is better. In Wisconsin, look for windows with a U-factor of .35 or lower.
Solar gain (SHGC) measures heat added by sunlight. Higher numbers mean more heat gain.
Visible transmittance measures how much visible light passes through the glazing.
Air leakage measures wind resistance. Lower is better (tighter seals).
Condensation resistance factor (CRF) measures how well condensation is prevented. Higher is better.