
Design Resources
Energy Efficient Windows: Understand the Parts
It’s easy to say that a product is energy-efficient, but the real question is: why? An energy-efficient window is not one component but rather, the sum of its parts. So why are some windows more efficient than others?

Understanding the individual components is helpful in answering that very question.
THE THERMOPANE
The glass unit in a window is referred to as the thermopane, which is in itself a combination of vital components. An efficient thermopane will have not only two or three panes of glass, but also the following:
- LowE glass: Low Emissivity (LowE) glass has a metal-like coating, which reflects long-wave heat energy back into your home in the winter, while heat rays are reflected towards the outside in summer. LowE also prevents fading by filtering UV rays.
- Inert gas, such as Argon: Argon is a clear, non-toxic gas used to fill the thermopane. Heavier than air, argon offers greater resistance to heat loss and reduces exterior noise.
- Low-conductivity or “warm edge” spacer: A spacer keeps the glass panes in a window the correct distance apart, but also plays a larger role in creating a thermal break, insulating the edges of the pane and reducing heat transfer.
THE FRAME
The frame material also contributes to the overall efficiency of a window. Vinyl (PVC) windows are constructed with many air chambers that make it a good insulator. Wood is also a good insulator; however, aluminum window frames conduct heat very rapidly and therefore require a thermal break to improve insulation values.
NO AIR LEAKS HERE
Look for a window that has durable, multiple weather-stripping. Good-quality hardware is also vital to a tightly sealing window, as are solid, well-formed joints.
Casement and awnings are, by design, more efficient in terms of airtightness. The wind will push the casement sash against the frame, creating a tighter seal. That being said, innovations in hardware and design mean that good-quality sliding windows can now perform at similar levels.