saying they are ‘low e’ windows. If yours aren’t then you have to make some checks by looking at the glass inside the frame. The windows have to be dual panes. The glass should be about 3/8″ thick in the frame. Depending on the maker there might be a film centered in the frame. That film holds the very thin metal covering that blocks sun’s heat. Sometimes the metal is put on the inside of the glass itself instead of a film. Either way, the view through the glass should be darker than the view through the open window because of the metal film. If your glass is single pane it’s not low e. If your glass is crystal clear it’s not low e.
.
