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Glass acts

Environmental IssuesEnergy Saving

Two layers of glass, insulating air spaces and high-tech reflective films can make top-line windows almost as warm as insulated walls. But whether you're considering replacements on an older home or units for new construction, shopping for true energy efficiency can get complicated.

The Department of Energy (DOE) says that in most homes new windows will reduce overall energy costs by up to 15 percent. Better yet, units carrying the Energy Star label are twice as efficient as the average windows manufactured 10 years ago, and 40 percent more efficient than products required under most building codes, according to the DOE, which promotes the Energy Star program.

In many cases, the investment in energy-saving features pays off. But in some cases the math is not encouraging. If you spend $200 a window and again as much for installation (times, let's say, 15 windows), you'll invest about $6,000. If you spend $1,000 on heating and cooling, and save 15 percent a year due to improved glazing, it will take about 40 years to break even.

Even so, you'll be more comfortable for the next 40 years, and you're house will be more valuable. The new windows won't sweat and peel paint. And windows with coated glass can reduce UV rays by up to 75 percent, and possibly save you from refinishing faded floors or replacing bleached out upholstery. But purely financial paybacks generally are most attractive on replacement upgrades on old, leaky windows (particularly single-glazed units) and also on new construction.

With old, inefficient windows, you're probably spending extra on utility bills, and will save a higher percentage of those higher costs every year. And on new buildings, you don't need to count installation costs in the extra investment because they are about the same for any new window, even one that is not very energy efficient. On an addition, you might spend 15 or 25 percent extra for high-efficiency units, and break even after only a few years.


Windows are promoted with tilt-in sash for easy cleaning and exterior cladding to eliminate repainting -- many features that you can see and test. You can't do that with energy efficiency. You have to compare an array of energy-saving claims. Many are confusing, and some are baloney that don't even account for the frame.

To shop effectively, consider three characteristics in addition to overall quality. The first is low-E, which stands for low emissivity. Most energy-efficient windows are low-E windows. They have a microscopically thin metallic layer that allows short-wave light to pass through while reflecting long-wave heat energy. You can see through it, but heat doesn't flow through as readily as it flows through standard glass. Most low-E glazing also cuts UV rays that can bleach wood and fabrics by about 75 percent.

The second is the U-factor, included on all labels from Energy Star and the National Fenestration Rating Council (NFRC). This measures the overall rate of heat flow through a window, including the frame. Technically, a U-factor is the inverse of an R-factor, the standard measure of heat resistance used on insulation. In a nutshell, the lower the U-value number, the better the insulating quality.

The third is the solar heat gain coefficient. This SHGC number, which ranges between 0 and 1, measures the solar radiation admitted through a window.

Lower numbers indicate less transmission of solar heat and save cooling energy in hot climates.

The best bet: look for ratings by Energy Star and the NFRC. All Energy Star windows carry an NFRC certification label rating U-factor and solar heat gain.

No single energy-rating program covers all windows. But you should be able to find different styles and sizes with an Energy Star label, including single and double-hung, casement, slider and fixed windows. Frame materials include wood, vinyl, aluminum and fiberglass.

After all the research, an energy-saving window has to become part of a wall. It's easy on new construction where openings can be tailored to fit. It's trickier on existing buildings, and gives rise to two main problems.

One is downsizing -- packing out your old opening to fit a smaller replacement.

This often creates strange looking trim details, aside from decreasing your light and view. The other is shoddy workmanship -- often occurring when a window sales company farms out installation to contractors you never meet, much less check -- until it's too late.

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Is it time for window replacement?

If a window simply shows signs of wear and tear or exposure such as cracked paint but operates normally, then it's likely time to refinish it. However, below are some clear signs that replacing windows is a priority:

1. Fog or moisture between the glass panes. If the seal between glass panes is broken, cold air and water can leak into the window. Moisture or fog in between the panes is a good indicator that the seal is broken.

2. Moisture or condensation. Windows that let in moisture can lead to more severe problems such as mold growth. Look out for condensation on the window or standing pools of water on the windowsill.

3. Wood decay. Windows without protected wood can decay and rot if they are exposed to harsh elements or if a home has termites. Signs that wood may be decaying include soft wood that breaks away easily in irregular pieces or wood that has moisture in it.

4. Problems opening or closing. In older homes, wood windows may have been painted over numerous times or may have become severely warped due to age and weather conditions. A window that doesn't open and close easily is more than just annoying; it's a safety issue and a sign that it's time for a replacement.

5. Drafts. There are many tests to determine if a window is drafty, such as placing a lighted candle next to the window to see if the flame moves. If it does, you have a draft and your energy bills are paying the price.

6. Excess noise. Typically, older single-pane windows don't block as much noise as new double-pane windows. If you can hear your neighbors chatting across the street as they are getting their mail, it's probably time to upgrade your windows.

Source: Jeld-Wen Windows & Doors

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