Here is a simple, three-step test to determine whether it is possible to cut your home heating bills by replacing your existing windows:
1. Stand in front of one of the windows.
2. Draw back the curtain.
3. Look at the window.
If what you are looking at is an old-fashioned wood-framed window with a single sheet of glass, the answer is almost certainly ”yes.”
In fact, energy experts say, older windows are one of the most significant sources of heat loss in the home. And now, with home heating bills at near-record highs, replacing drafty old windows with new energy-efficient models is beginning to make more and more sense for many homeowners.
”There are basically two types of window replacement options,” said Jennifer Grove, marketing manager for Pella Windows and Doors, a window manufacturer based in Pella, Iowa. ”One would be a full-frame replacement,” she said. This is needed when both the window and the existing frame must be replaced — usually because the frame itself is rotted or otherwise damaged.
The other option — replacement of just the window while leaving the existing frame in place — is more common, less expensive and easier to accomplish.
”What we’re talking about is a replacement window unit that is custom-sized to fit the existing opening,” Ms. Grove said, explaining that the windows are individually manufactured to measurements provided by the homeowner. ”You don’t have to disturb any of the interior walls or woodwork to install them, and it’s so simple to do that do-it-yourselfers can usually do it themselves.”
Ms. Grove said that installing a Pella Precision Fit replacement window requires the removal of only the wood strips that hold the windows in place. Once those strips are removed, the original windows can be taken out of the frame and replaced with the new window assembly.
”You can get our wood replacement windows for about the same price you would pay for vinyl replacements,” she said, adding that Pella’s Precision Fit wood windows range in price from about $300 to $550, including installation.
Brian Ciechanowski, the owner of Tri-Pane Installations, a replacement window contractor based in Farmingdale, N.Y., said homeowners who want vinyl replacement windows — which are popular because they never have to be painted — should be aware that not all vinyl windows are created equal.
”Buying a window is a little like buying a car,” Mr. Ciechanowski said. ”You have economy, midpriced and luxury models.”
The ”economy” model vinyl window sash and frame assembly, he said, is generally held together with screws. Such windows are often advertised for as little as $169 installed. ”It’s not a very good window, though, because after a while, the parts start to separate,” he said.
The midpriced model, which costs about $225 to $275, uses screws to hold together the frame, but employs a welding process to construct the sash — the casing around the window glass itself. And the top-of-the-line vinyl replacement window, he said, uses welded seams for both the frame and sash, making the entire assembly more sturdy and resilient.
Virtually all replacement windows sold today, he said, are at least double-glazed, meaning that there are two panes of glass encasing an insulating area of ”dead air” between them.
And the better windows contain energy-saving features like foam-filled frames, ”low-emissivity” coatings — which prevent heat loss from inside the house while protecting furniture and furnishings from the effects of ultraviolet light from the outside — and argon gas instead of just ”dead air” in the space between panes.
”Our fully welded windows run from $300 and up,” Mr. Ciechanowski said, adding that the energy-saving features can add another $75 per window.
One way that homeowners can judge the quality of a particular replacement window is by using a rating system developed by the National Fenestration Rating Council, a not-for-profit testing organization based in Washington.
”When it comes to the energy performance of windows, the N.F.R.C. is basically the Good Housekeeping Seal of Approval,” said Leonard Greenberger, a spokesman for the organization. The council’s ratings on hundreds of windows are available on its Web site at www.nfrc.org, and they are also on stickers that are placed on any windows that have been tested.
Mr. Greenberger said that while the council bases its ratings on various parameters of window performance, the most useful rating is the window’s ”U-value.”
”The U-value measures how good a window is at keeping heat inside a home,” he said, explaining that the lower the U-value, the better the window.
”The very best windows have a U-value as low as 0.15,” he said, adding that the average U-value for a good replacement window is about 0.45 and the least efficient models have a U-value of 1 and higher.
Another important rating provided by the council is what is known as the ”solar heat gain coefficient.”
”That tells you how much solar heat is coming into the house through the window,” he said, adding that the coefficient ranges from 0.085 to 0.05. ”The higher the number, the better the window is at keeping solar heat out.”
Mr. Greenberger pointed out that since solar heat gain would be considered a benefit to homeowners in colder northern climates, windows with a lower solar heat gain coefficient would generally be considered preferable to those with a higher rating. The opposite would apply, however, in hot southern climates where heat from the sun is best kept outside.
For those who want the ultimate in energy efficiency when buying replacement windows, the so-called superwindow may be just the thing.
”The very best window out there is a triple-glazed double-soft-coat low-e window with two layers of krypton gas,” said Gerald Damora, the owner of Morris Window and Siding, in Randolph, N.J.
Mr. Damora explained that with a triple-glazed window there are three separate pieces of glass that create two insulating dead-air pockets. Those spaces are then filled with krypton gas — which is heavier than argon and thus better at insulating.
”That gives you a U-value of about 0.19,” he said. ”And that is fabulous.”
Such superwindows also have soft-coat low-emissivity coatings on all the glass surfaces. ”A hard-coat low-e coating is applied as the glass is being made,” he said. ”A soft-coat low-e coating is applied afterward and is much thicker and much better.”
While such windows are more expensive than even the best double-glazed replacement units — a triple-glazed superwindow will cost between $700 and $900 installed — they are significantly better at saving energy. In fact, Mr. Damora said, while replacing a residence’s single-glazed windows with high-efficiency double-glazed models will result in a savings of between 10 and 15 percent on heating bills, using a triple-glazed super-windows will result in a savings of as much as 47 percent.
”Not everybody can afford these windows,” Mr. Damora said. ”But think about it. If you put in a new kitchen for $40,000, you’re not going to see a return on your investment until you sell your home. When you put in triple-glazed, high-performance windows, you begin saving money the minute the installer walks out the door.”