With the AC on, why is it still hot by the window? — The heat isn’t being blocked; you just can’t see where it’s getting in

Radiant heat passes straight through ordinary glass — invisible, silent, and working against your AC all day. See how vacuum glazing stops it at the window.

Why does the spot by the window stay hot even with the AC running? This article breaks down the science: heat enters through glass along two invisible paths—direct solar short-wave radiation and heat transfer driven by indoor-outdoor temperature differences. It explains the three metrics that actually decide window performance (U-value, SC/g-value and LSG), compares four window systems from single-pane to vacuum glass, and shows why SuperVIG® vacuum glass addresses both heat paths at once.