Replacement Windows

What's the difference between argon gas and krypton gas?  And what's this Low-e business when we're talking about replacement window glass?  Check out our glossary.

Window Buying and Installation Glossary

Argon gas

A gas several times more dense than air, argon is injected between window glass to inhibit the transfer of cold or heat between the outside and inside.  Contrast with krypton gas.

Balance system; balancer

The method by which the sash is held in place when the window is open.  Typically, a spring, counterweight, or friction device. 


Two panes of glass between you and the exterior.  The space between window glass panes is often filled with gas such as argon or krypton or may simply be an air vacuum.  Double-pane has largely become the standard for most windows.  Contrast with triple-paned windows.

Krypton gas

A gas denser than air and argon gas that is forced between double-paned windows (or triple-paned) to slow the transmission of outside temperatures to the inside.


This "low emissivity" coating reflects sun back from the outside, while allowing most of the light to come through.


A small tab on the inside of the window that allows sash to open only a few inches.  Note:  despite the name, this should not be used at night or to keep children in, because the tab is easily broken.


The component of the window that contains the glass and moves upward or outward (except in the case of fixed-glass windows).


Three panes of glass between interior and exterior.  Used mainly in extremely cold climates.  Contrast with double-paned windows.

Learn More