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2018 National Home Improvement Estimator, All Rights Reserved Page 147

Chapter 8, Windows

Windows can be an important (and expensive) part of any home improvement project. Loose-fitting,
single-glazed windows are a major source of heat loss and gain. Wood windows in older homes often
look similar to the eyesore in Figure 8-1. If your first instinct is to replace the window, keep reading.
That may not be the best choice. This chapter explains why.

About one-quarter of the heating and cooling load in a well-insulated home is the result of heat transfer
through windows. Old window frames and sash tend to be very porous, admitting streams of outside air
during both heating and cooling seasons. Modern windows have superior weatherstripping and are much
tighter. In fact, modern windows are so tight that a home can develop condensation problems and a
musty odor after leaky, old windows are replaced. Modern windows have insulated frames and dual
glazing with about 1/2" of dead air space between the panes. In better-quality insulated windows, this
dead space is filled with argon gas, which transfers even less heat than dead air. Low-emissivity (Low-E)
glass has two invisible layers of microscopically-thin silver sandwiched between anti-reflective layers of
metal oxide. Low-E glass admits sunlight but blocks radiant heat from escaping during the winter.
During the cooling season, Low-E glass reflects back to the exterior as much as 25 percent of
unwanted solar heat. Low-E coatings also block more than 80 percent of the ultraviolet light that tends
to fade fabrics. Glass edges in better-quality insulated windows are sealed with “warm edge” spacers
that transfer even less heat around the glass perimeter.

Modern windows have clear advantages over windows installed in homes before about 1970. But these
advantages come at a price, especially if windows have to be custom-made to fit the opening. Before
recommending replacement, take a few minutes to examine the existing windows.

Check the tightness of fit. A window sash that rattles in the frame probably leaks cold air in the winter,
hot air in the summer and water during heavy rain. Check the operation of the window. Old double-hung
and single-hung wood windows seldom operate smoothly. You may find many that are painted shut.
Years of re-painting has sealed and immobilized the sash in the frame. That may reduce leaking but it
also eliminates venting as an option. Old casement and awning windows tend to warp at the top and
bottom. Dark stains on the sash and sill are usually caused by condensation running down the glass. If
you see condensation stains, check for softening of the molding and sill.