Modern energy efficient windows use multiple technologies that work together to dramatically outperform older single-pane or standard double-pane windows.
Low-emissivity coatings on glass reflect heat back to its source — keeping heat in during winter and blocking solar heat gain in summer. Low-E glass is standard in all energy efficient replacement windows.
The space between panes is filled with inert gas (argon or krypton) rather than air. These gases conduct heat less efficiently than air, reducing thermal transfer through the glass unit.
The spacer separating the panes is a significant source of heat loss in standard windows. Warm-edge spacers made of foam or hybrid materials dramatically reduce edge conduction.
Single-pane windows have an R-value of approximately R-1. Modern energy efficient double-pane windows achieve R-3 to R-4, and triple-pane windows reach R-6 to R-8. In NJ, where heating and cooling costs are significant, replacing old windows with energy efficient models typically pays back in 7–15 years through utility savings.
