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 establish its energy-efficiency ratings:
Traditional operable window types include the projected or hinged types such as casement, awning, and hopper, and the sliding types such as double- and single-hung and horizontal sliding. This section on Operator Types describes how these typical windows work.
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.
The material used to manufacture the frame governs the physical characteristics of the window, such as frame thickness, weight, and durability. It also has a major impact on the thermal characteristics of the window. This section on Frame Types describes the performance impact of different frame materials and how they influence the total window performance.