"New Windows Can Cut Your Energy Bills Significantly. The Saving Could Justify The Upgrade!"
With last summer's stratospheric gasoline prices a fresh reminder, and the prospect of higher home-heating costs looming as well, many homeowners may wonder whether it's time to replace aging, drafty windows with efficient, tight-fitting ones. Old windows--a single sheet of plain glass in a wood or metal frame--allow heat to pass through the glass and air to migrate through gaps and cracks in the frame. Modern windows incorporate a frame made of all-vinyl or wood, often covered in vinyl or aluminum, with two or three sheets of glass that are sometimes specially coated and separated with air or another gas to help cut energy use.
You'll usually save money by replacing old single-glazed windows with virtually any energy-efficient new window. But you aren't likely to recoup the initial outlay through lower heating and cooling bills for 20 years or more. That's why it makes the most sense to install new windows when the old ones have deteriorated, when you're remodeling, or when you want windows that are easier to wash and maintain. (If enough homeowners installed new windows, however, the individual small savings could add up to significant nationwide savings of energy, with attendant benefits to the environment.)
Determining which windows to buy, however, can be daunting. New standardized labels, so far required in only a handful of states, are supposed to make it easier to comparison shop for new windows. But not all windows carry the labels, which cover only energy efficiency, not wind and rain resistance, durability, or convenience.
To give you information that the labels don't, we hired an outside lab to test 16 double-hung and 2 casement windows from Andersen, Marvin, Pella, and other major manufacturers. We chose double-glazed windows with argon between the panes and a low-E coating. That's a sensible package in most parts of the country. Our windows, sized for an opening of about 3x5 feet, ranged from $150 to $415.
The type of glazing can affect a window's price and energy performance even more than the frame. Here are factors to weigh:
Single, double, or triple glazing. A single sheet of clear glass allows the highest transfer of energy, offering little insulation against frigid winters or searing summers.
Double-glazed windows have a sealed space between two panes of glass to provide an added layer of insulation. Compared with a single pane, double glazing can cut heat loss of the window nearly in half.
Triple-glazed windows have a higher insulating value still, but few manufacturers offer them. The extra layer adds to the weight and cost.
Gas filling. The gas in the gap between the panes improves the window's insulating value. Ordinary air works fine and is sometimes a manufacturer's "standard" option. A gas like argon will provide better thermal performance. Some manufacturers make argon filling standard. Top-of-the-line glazings sometimes incorporate more-exotic gases like krypton for still better insulation. Like triple glazing, however, this option isn't seen very often.
Plain glass or "low-E" coating. Clear glass allows large amounts of radiant energy (heat in from the sun in the summer, heat out from your house in the winter) to pass through. Low-E (for low-emissivity) coatings add more insulation value to the window by reflecting heat back into the house and blocking some heat from the sun. The coatings can be fine-tuned for different climates, producing Southern and Northern windows, for example. Sometimes multiple coatings are applied to block even more radiant energy. Some coatings may darken the glass, like tinted glass in a car, an effect some people may find undesirable. Check a sample at the store.
Windows like these can be made for new construction (nailed into an opening, then finished with trim), or as a replacement for an existing window. Some come in custom sizes, others only in stock sizes. The materials that make a window frame can affect energy efficiency, maintenance, and price.
WOOD: For sheer elegance, natural wood is hard to beat, though it usually costs more than vinyl and requires painting or staining. To minimize maintenance where it's needed most--the exterior side exposed to the weather--many manufacturers cover (clad) the wood in vinyl or aluminum.
VINYL: Many vinyl windows feature sturdy welded corners that are less likely to pull apart from repeated swelling and shrinking as temperatures rise and fall. Vinyl isn't usually available in many colors.
ALUMINUM: Aluminum windows have dwindled in popularity as vinyl's star has risen. Aluminum's biggest drawback: It conducts heat readily. That can make the area around the window feel chilly. In places like New England, a simple aluminum frame can become cold enough to condense moisture or frost on the inside. (In the South, where heat loss is less of an issue, aluminum can be a good choice.) Better aluminum windows are "thermally broken," with insulating material between interior and exterior components.
A VINYL/WOOD COMPOSITE: Andersen and other manufacturers are beginning to offer composite frames, claiming they offer the strength and durability of wood with the low upkeep of vinyl. For example, the Andersen Renewal and Millennium windows use frames made from a mixture of wood fibers and vinyl. According to the company, the compound is less susceptible to temperature changes than are other materials. In our tests, the Millennium performed quite well and proved very durable, although other, less-expensive Andersen windows also did well.
What Do The Numbers Mean?
Window makers use the term U-factor as a measure of thermal performance. It describes a window's ability to conduct heat. The Ratings also give the better-known R-value--the inverse of the U-factor--which describes insulating ability. The higher the R-value (or the lower the U-factor) the better a window will keep your home cool in summer and warm in winter.
Weathering The Elements
The acid test of any window is how well it holds up to the elements. So our tests focused on other aspects of performance, not just thermal efficiency.
First, we gauged each window's ability to block drafts, repel water, open smoothly and easily, and close snugly. Next came two weeks of accelerated punishment, including alternating periods of high heat, frigid temperatures, radiant heat, and simulated rainstorms. Then we checked for structural changes and re-evaluated performance.
Wind and rain leakage. When new, most windows did a very good or excellent job at sealing out fairly strong winds when the outside thermometer registered about 70° F. But when we dropped the temperature to zero--which can cause weather stripping and other components to shrink or stiffen--only the Marvin Clad Ultimate; the Andersen Tilt-Wash, Narroline, and casement; the Pella ProLine; and the CertainTeed Bryn Mawr II performed extremely well.
Five windows performed poorly in the cold; they leaked at least four times as much air as the highest-rated windows.
Most windows did a decent job of repelling rain; seven prevented all water leakage in the face of 50-mph winds.
The windows that fared worst in the rain were the Alside UltraMaxx, Crestline VinylCrest, WeatherShield Visions 2000, and Wenco Series 8.
Durability. Most windows held up remarkably well.
The Crestline VinylCrest suffered the most structural changes--bowed stiles, rails, and jambs--but the Wenco Series 8 had the worst fall-off in performance.
Ease of use. Most new double-hung windows have tilting sashes, a very handy feature that lets you pivot them inward for easier cleaning. Among the tested windows, only the Andersen Narroline has non-tilting sashes. With most windows, you simply flip a lever or two to tilt the sash inward. But with some, you must pull the sash out of its vinyl track.
To help keep out water, some double-hung windows have a thin lip--a strip of wood or vinyl about an inch high--that rises from the sill. You may need to work around the lip when installing an air conditioner.
If you decide to replace old windows with new, high-efficiency ones, be sure they're designed for the weather in your area:
IN THE SOUTH: Cooling costs predominate here, so look for double glazing and a low-E coating. Give first consideration to windows with a low solar heat-gain coefficient; the U.S. Department of Energy recommends a number of 0.4 or less.
IN THE CENTRAL STATES: Here, heating and cooling share the spotlight. Again, look for double-glazing with a low-E coating. You'll also want high insulating value and a solar heat-gain coefficient of 0.55 or less.
IN THE NORTH: Heating bills constitute the biggest concern. Give priority to well-insulated, double-glazed windows that are draft-free. A low-E coating isn't essential.
The best double-hung window was the Marvin Clad Ultimate, $310. The wood-frame Pella ProLine was nearly as good and sells for a lot less. At $180, it's rated A CR Best Buy. The standout vinyl window was the CertainTeed Bryn Mawr II, $180. The Survivor 5500, $155, is also a very good choice.
On The Corners
The last time we tested windows, in 1993, we advised readers to avoid vinyl windows whose corners are screwed together because they may start to pull apart after being exposed to heat and cold.
We have to temper that advice. One window we tested, the Simonton Reflections 5050, $155, has mechanically fastened corners, not welded ones like the other windows in the group. The Reflections performed very well overall, earning high marks for wind and rain resistance and for durability. If we had included it in the Ratings, the Reflections would have been the third-ranked vinyl window, similar in performance to the Lowe's Survivor 5500.
Windows The Tests Behind The Ratings
We hired an outside lab to test windows (without screens) fitted with double-pane glass that has a low-E coating and argon between the panes. Material for the frame and sashes is typically aluminum- or vinyl-clad wood or all-vinyl. The Andersen Millennium is made of extruded wood fibers and vinyl. The Crestline CrestWood has a vinyl frame, vinyl-clad wood sashes, and interior wood trim. Overall score is based mainly on R-value, wind- and rain-resistance, and durability. R-value indicates the window's overall insulating value. It's more familiar than the U-factor. The higher the R-value and the lower the U-factor, the better a window can keep your home cool in summer and warm in winter. Performance judgments show how well the windows kept out 25-mph wind at different outdoor temperatures and windswept rain in laboratory tests. Durability indicates how well the windows performed after two weeks of severe temperature fluctuations and intermittent spraying with water.
Condensation shows how well the window resists getting wet on the inside in cold weather.
Ease of use covers design of handles and such.
Comments identify special features and point out additional information. Price is the estimated average.
Installation is extra.
Except as noted, most have handles. Double-hung models have tilt-in sashes. Screens are optional. Most windows are available in stock and custom sizes.
Windows Within Types, In Performance Order
Brand and Model
Overall score R-value
Wind Rain Durability
Condensation Ease of use
Marvin Clad Ultimate $310 Aluminum clad 2.9 0.34
Marvin comments: Very good overall. Sash handles optional. Lip on sill may interfere with air conditioner.
Andersen Tilt-Wash 235 Vinyl clad 3.0 0.33
Andersen comments: Very good overall. Some parts warped or loosened in durability tests. Comes in stock sizes only. Lip on sill may interfere with air conditioner.
Pella ProLine A CR Best Buy 180 Aluminum clad 3.1 0.32
Pella comments: Very good overall. Some parts warped or loosened in durability tests. Sash handles optional. Comes in stock sizes only.
CertainTeed Bryn Mawr II 180 Vinyl 2.9 0.35
CertainTeed comments: Very good overall. Has locks to limit sash opening and sliding half screen. Comes in custom sizes only. Lip on sill may interfere with air conditioner.
Andersen Narroline 205 Vinyl clad 2.9 0.35
Andersen comments: Very good overall. Some parts warped or loosened in durability tests. No sash-tilting feature. Comes in stock sizes only.
Pozzi Clad 370 Aluminum clad 2.9 0.34
Pozzi comments: Very good overall. Some parts warped or loosened in durability tests. Comes with full screen. Sash handles optional. Lip on sill may interfere with air conditioner.
Andersen Millennium 415 Composite 2.9 0.35
Andersen comments: Very good overall. Lip on sill may interfere with air conditioner. Company says unit is identical to Renewal, which is more widely available.
Survivor 5500 (Lowe's) 155 Vinyl 2.4 0.41
Survivor comments: Very good overall. Some parts warped or loosened in durability tests. Has locks to limit sash opening and sliding half screen. Lip on sill may interfere with air conditioner.
Crestline CrestWood 235 Hybrid 3.2 0.31
Crestline comments: Very good overall. Some parts warped or loosened in durability tests.
Alside UltraMaxx 170 Vinyl 2.8 0.36
Alside comments: Good overall. Has locks to limit sash opening, and sliding half screen. Comes in custom sizes only.
Caradco Guardian 265 Aluminum clad 2.8 0.36
Caradco comments: Good overall. Some parts warped or loosened in durability tests. Lip on sill may interfere with air conditioner. Comes in stock sizes only.
WeatherShield Visions 2000 240 Vinyl 3.0 0.33
WeatherShield comments: Good overall. Has locks to limit sash opening.
WeatherShield comments: Good overall. Some parts warped or loosened in durability tests. Lip on sill may interfere with air conditioner.
Crestline VinylCrest 195 Vinyl 2.9 0.34
Crestline comments: Good overall. Some parts warped or loosened in durability tests. Lip on sill may interfere with air conditioner.
American Craftsman 8500 (Home Depot) 175 Vinyl 2.5 0.40
American Craftsman comments: Good overall. Some parts warped or loosened in durability tests. Has locks to limit sash opening and sliding half screen. Lip on sill may interfere with air conditioner.
Wenco Series 8 150 Vinyl 2.7 0.37
Wenco comments: Good overall. Some parts warped or loosened in durability tests. Lip on sill may interfere with air conditioner.
Andersen 280 Vinyl clad 3.3 0.30
Andersen comments: Very good overall. Some parts warped or loosened in durability tests. Comes in stock sizes only.
CertainTeed Bryn Mawr II 290 Vinyl 2.6 0.38
CertainTeed comments: Very good overall. Some parts warped or loosened in durability tests. Comes with full screen. Comes in custom sizes only.
If you're considering new windows, not just storm windows and better weather stripping, what kind of saving can you expect from the different types of glazing available? To find out, we tested three versions of the WeatherShield WeatherShield: The basic Insulated, which features plain air between the panes and lacks a low-E coating; the mid-line (the one we rated), with argon gas between the panes and a low-E coating; and the top-of-the-line Value R5, with argon/krypton gas and two low-E coatings. (The "R5" is the insulating value in the center of the glass; the window's overall R-value is much lower.)
Using the RESFEN 3.1 computer program developed at Lawrence Berkeley National Laboratory with our test results, we calculated the potential energy savings for a hypothetical house in three localities: Madison, Wis., a Northern city where heating costs predominate; Phoenix, Ariz., a Southern city where bills run highest for air conditioning; and Kansas City, Mo., a Central states area where both heating and cooling costs are significant.
We estimated the annual savings, based on replacing 20 3x5-foot single-pane windows in a 2,000-square-foot house with the various versions of the WeatherShield window. We reckoned on electricity for cooling and natural gas for heating, at the national average utility rates of 8 cents per kilowatt-hour for electricity and natural gas at 70 cents per therm. (Of course, changing any of those variables would change specific dollar amounts.)
Replacing existing single-glazed windows can yield the biggest annual savings in the South--but only with the most expensive glazing option. But even then, it would take more than 30 years of lower energy bills to pay for the new windows--without installation.
In the North, insulated windows yielded the greatest incremental savings, while savings in the Central region doubled with an upgrade to low-E with argon. Moving to the Value R5 windows in these regions would have little benefit.
The frame of a new energy-efficient window will be made of vinyl or of wood clad in vinyl or aluminum for durability. Glazing will be two panes of glass sealed around the edges and often treated with a low-E coating to cut heat loss. In our tests, most windows proved to be well made, able to withstand temperature extremes, wind, and rain.
The Effect Of Low-E Coating
A low-E coating on a window makes the glass act something like a two-way mirror, reflecting heat rather than letting it escape. The image here, captured by our infrared camera, shows the kind of difference a low-E coating can make, blocking the heat emitted by a person standing behind a window (we had removed the lower sash of each window). As you can see, the low-E coating in the window on the left effectively blocks almost all the heat, while the uncoated window on the right lets heat pass through.
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