Types and Parts
The technologies that make windows efficient go beyond just the glass panes – they are found in the frames and inside them as well, including the internal spacers that hold the glass in place. NFRC’s ratings system evaluates all these parts of a window to determine its energy-efficiency rating:
Single-glazed windows have one pane of glass and typically cost less. Double-glazed windows have two panes, and balance cost and efficiency. Triple-glazed windows use three panes and are the most efficient.
Windows with more than one pane have a fixed gap between them, and filling that space with a safe, odorless, and colorless gas boosts efficiency. In cold climates, the gas reduces heat loss through the glass. In hot climates, it reduces unwanted heat gain.