Replacing windows

Consider use and appearance as well as the type of glass
By James Dulley
Replacing windows

Double-hung windows have hidden latches that allow each sash to be tilted in for easy cleaning. (Photo: Weathershield)

It can be very difficult to sort through marketing hype from salespeople to make window decisions. Replacing windows is expensive, and usually energy efficiency should not be your only reason to purchase new ones. Other efforts will save more money, and you can also make existing windows more energy efficient. But if you truly need new windows, there are some considerations.

Selection not only depends on the efficiency characteristics of the window, but also on your specific house and family lifestyle. For example, you may want a view of a particular area outdoors or want springtime ventilation whereas your neighbor may keep their blinds closed and air-condition continuously.

The three main decision criteria for selecting replacement windows are glass type, window style and frame material. Regarding energy efficiency, the glass type and style of window are more important than frame material.

Glass types

Because glass is most of the window, the type you choose is the key to its energy efficiency. Double pane glass with low-E (low-emissivity) coatings and inert gas in the gap between the panes is adequate for most climates. Triple pane glass may make sense for severely cold climates.

The location of the low-E coating on the various pane surfaces, often more than one, affects whether the glass is better for winter or summer savings. You may end up selecting different glass options for different windows in your house.

Style of window

The proper style of window depends primarily on the appearance and features you desire, more than energy efficiency characteristics. For example, people often select double-hung windows because they can be tilted in for easy cleaning from indoors. But windows that close on a compression seal, such as casement and awning windows, tend to provide the best long-term airtight seal.

Frame materials

The four most common frame materials for residential windows are vinyl, fiberglass, wood, and clad wood. Each has its own advantages. Vinyl is energy efficient and virtually maintenance free. They also are made to the precise dimensions of the window opening instead of having to shim out standard sizes.

To attain adequate rigidity, the vinyl frame extrusions have many webs and chambers inside. These chambers create natural insulation. For greater R-value, several vinyl window manufacturers inject expanding foam insulation inside the chambers as the frame is assembled.

Always look for sash frames that have welded corners for strength. Because the outer window frame is screwed rigidly into the window opening framing, welded corners in it are not as important as with the sash frames. If you select vinyl frames for large windows, especially in hot climates, they should have steel reinforcement internally. When vinyl gets hot in the sun, it loses strength and rigidity.

Fiberglass frames are extremely strong and can be painted any color to match interior or exterior house colors. Because their primary component is glass, fiberglass frames expand and contract with temperature changes about the same rate as the glass panes to minimize stress..

When maintained, wood window frames have a very long life. Wood frames are also the most attractive. Their drawback is some regular maintenance is required for appearance and energy efficiency.

Exterior vinyl- or aluminum-clad wood frames greatly reduce the maintenance requirements. The natural wood can still be exposed on the indoor surface so they look like wood windows from indoors. Some vinyl and fiberglass frames are available with natural wood indoor cladding to provide the appearance of real wood frames.

About the Author

James Dulley is an engineer and syndicated columnist for the National Rural Electric Cooperative Association. www.dulley.com

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