The window where you stand to watch the birds feed or your roses bloom could be the biggest energy drain on your house. Windows are huge thermal...

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The window where you stand to watch the birds feed or your roses bloom could be the biggest energy drain on your house.

Windows are huge thermal holes, places where you can lose as much as 30-40 percent of your heating and cooling costs, according to industry experts.

In fact, replacing all residential windows in the United States with more efficient models would save $7 billion over the next 15 years, according to the National Fenestration Rating Council, a nonprofit group that developed a window energy-rating system based on whole-product performance.

Choosing replacement or new windows for your home is a daunting task because there are more than 300 manufacturers making them.

Each company’s products have their own bells and whistles — blinds or grilles between panes, tilt capabilities for easy cleaning and, just recently, storm-protection features — and you pay for those niceties.

Window terms

Look for the label that gives you energy and other performance ratings, including:

U-Factor. Measures how well a product prevents heat from escaping. U-Factor ratings generally fall between 0.20 and 1.20. The insulating value is indicated by the R-value, which is the inverse of the U-value. The lower the U-value, the greater a window’s resistance to heat flow and the better its insulating value.

• Argon is an inert, nontoxic gas used in insulating glass units to reduce heat transfer.

• Low-emittance (Low-E) coating. Microscopically thin, virtually invisible, metal or metallic-oxide layers are deposited on a window to reduce the U-factor by suppressing heat flow. Low-e windows cost about 10-15 percent more than regular windows, but they reduce energy loss by 30-50 percent.

Solar Heat Gain Coefficient (SHGC). Measures how well a product blocks heat caused by sunlight. SHGC is expressed as a number between 0 and 1. The lower a window’s solar heat-gain coefficient, the less solar heat it transmits, which ultimately affects your cooling bills.

Visible Transmittance (VT). Measures how much light comes through a product. VT is expressed as a number between 0 and 1. The higher the VT, the more light is transmitted.

Air Leakage (AL). Indicated by an air-leakage rating expressed as the equivalent cubic feet of air passing through a square foot of window area (cfm/sq ft). Heat loss and gain occur through cracks in the window assembly. The lower the AL, the less air will pass through cracks in the window assembly. Optional rating.

Condensation Resistance (CR). Measures the ability of a product to resist the formation of condensation on the interior surface of that product. The higher the CR rating, the better that product is at resisting condensation formation. This rating cannot predict condensation, but it can provide a credible method of comparing the potential of various products for condensation formation. CR is expressed as a number between 0 and 100. Optional rating.

More information

For more terms, visit

Research the ratings of window styles by 343 manufacturers through the Certified Products Directory Searchat

Source: National Fenestration Rating Council

“When you compare the prices of windows, you can’t make a blanket statement,” says Robert Criner of Criner Construction in Yorktown, Va.

“All have different lines within their banner of manufacturing. And it’s all in a state of evolution constantly.”

There are a lot of nationally recognized brands out there that contractors seem to favor — Andersen, CertainTeed, Caradco, Lyf-Tym, Marvin, Norandex, Pella, Peachtree and Simonton. Each company offers several lines with features that fit most pocketbooks. For a mid-range replacement vinyl window, you can expect to pay about $350 to $400 per standard-size, double-hung window, installation included, depending on construction costs where you live.

Choosing a window

There is, however, some rhyme and reason to selecting a window meant for your needs.

First, consider your environment and the architecture of your home. If you are replacing or adding windows, try to match or complement what’s already on the house.

You also need to choose a window that’s right for your climate and whether cooling or heating is more important to your comfort.

Evaluate what kind of maintenance you want to do on the windows. Wood ones need paint or stain; vinyl ones require gentle cleaning.

Window improvements

There are also some new improvements available in windows. Fiberglass-frame windows are arriving on the market and are expected to make a major impact, just like the strong fiberglass doors that have become so popular.

And, if you hate cleaning windows, you’ll like the fact that PPG makes SunClean, a self-cleaning glass that can be used in residential windows.

Regardless of what brand or style window you prefer, look for the Environmental Protection Agency’s Energy Star rating on the label because multipane glass is no longer the main measure of a good window, according to the EPA. Welded seams; Low-E solar-protective coatings; gases between the panes; good weather stripping; and glass spacers made from steel, foam, fiberglass or vinyl — not aluminum — are some of the hallmarks of a quality window.

Learn more

These Web sites offer information on how to buy and install new and replacement windows, as well as other helpful information about energy-related topics for your home:

Efficient Windows Collaborative:

Energy Star Windows Program:

National Fenestration Rating Council:

U.S. Department of Energy:

National Renewable Energy Lab:

Center for Sustainable Building Research: /

And, if you live in a waterfront location frequented with strong winds and salt spray, consider thicker glass panes, maybe even laminated ones.

But there’s one characteristic you want to get with any window you select — a good, reputable warranty. Any warranty is only as good as the company that stands behind it, so be sure to deal with a company that has a history of backing its product and taking care of its customers.

“I go for looks, how they operate, but mainly who is going to stand behind them,” says David Cross of Cross Remodeling in Hampton, Va.

Dennis VanCamp with Hatchett Home Improvement in Newport News, Va., agrees you should carefully evaluate the warranty you get.

“In the past there have been several contractors selling windows with lifetime warranties, but after a couple years when a problem arose, neither the contractor nor the manufacturer were to be found,” he says.