Window glass spacers: more important than they seem

Today's double- and triple-pane glass units require the use of spacers between the panes. Situated along the outer edges of the glass, the spacers allow ambient air or gas to fill the space between the panes, providing the glass unit with another source of insulation beyond low-e coatings. The type of spacers used and how they are sealed to the glass contribute to the window's insulating value.

Types of spacers

1. Hollow aluminum square tubes. Still probably the most commonly-used, spacers of this type are usually bonded to the panes of glass with a sealant. Because the glass units are sealed in an environment where humidity can be present, a silica drying agent is inserted into the hollow tube to absorb any moisture that could condense between the panes of glass.
2. U-channel, warm edge. PPG's Intercept system is an example of this type of spacer. The tin-plated or stainless steel, U-channel spacer stops the transfer of heat and cold because the open end of the "U" breaks direct contact between the layers of glass and the metal. As a result the glass stays warmer. Desiccant, putty-type material is applied to the inner surface of the spacer to absorb moisture and prevent condensation from forming between the glass panes.
3. Foam. Super Spacer by Edgetech is a strengthened foam product, and because there is no metal at all between the glass panes to transfer heat and cold, it is also considered "warm edge." The foam can expand and contract as the temperature changes, allowing continual contact between the sealant and the glass. This prevents the seal from breaking.

Manufacturers choose spacers based on cost and desired performance features. By pairing a particular spacer system with their selection of low-e glass offerings, they can create a variety of glass units with u-values to suit every climate zone. The same type of low-e glass -- for example, pyrolytic, one-coating glass -- teamed with any one of these three types of spacers produces three glass units, each with a different u-value.

Window manufacturers brand their glass units to differentiate them from the competition, but what you need to compare are the insulating values. Make sure you're getting the best glass based on Energy Star requirements for your home's location.