New windows can make a dramatic difference in any home, whether you want to improve its appearance, open up a spectacular view or simply replace worn units that seem to let in more wind and rain than they keep out. Modern window frames cut air infiltration down to almost zero and, when used with advanced glazings, can slash up to 40 percent off your heating and cooling bills. Some windows also free you from periodic painting. Still others rival fine cabinetry in eye appeal.

Manufacturers have expanded those choices with new frame materials, glazing and installation options. Indeed, “replacement windows” are no longer limited to the kind that involve ripping out the old window and installing a new prime window. They now include money-saving versions that allow you to replace the glass and sash without replacing the frame. While the added options also expand your decisions list, new labeling programs make choosing well-built, energy-efficient windows easier than ever.

Material Choices
Windows frames come in a number of different materials, including wood, vinyl aluminum, fiberglass and composite plastic.

Vinyl-frame windows are the most affordable — as little as half the price of comparable wood-frame versions. They’re also especially energy efficient, thanks to a honeycomb of chambers that boost insulating ability by trapping air, and can be built to fit any size opening. And unlike wood, they never need repainting, though colors are limited.

Vinyl-frame windows first appeared in the 1970s when small fabricators produced custom replacement options in sizes not offered by manufacturers of stock wood windows. Today, nationwide companies offer a variety of units in stock and custom sizes. Even traditional wood-window companies now offer vinyl-frame replacement lines.

When shopping, look for a uniform color throughout the frame. Also look for joints that are heat-welded rather than joined with screws or other fasteners. You can expect a two- to six-week wait if you order custom units.

Wood-frame windows are slowly losing their market dominance to vinyl, though they’re still considered the gold standard by many professional installers and homeowners. They’re strong, beautiful and relatively energy efficient. As might be expected, good ones also cost the most. The knock against them is maintenance: They must be painted or stained periodically to look good and remain protected from the elements.

Some manufacturers address that required upkeep by cladding the wood with vinyl or aluminum. The result is a tough, maintenance-free exterior and a natural-wood interior that you can paint or stain. These advantages mean clad-wood windows usually cost more than ordinary wood. When shopping for wood windows, look for easy operation and tight-fitting corners. Be sure any exposed wood is free of blemishes and that finger joints aren’t visible.

Aluminum-frame windows offer the low cost and low maintenance of vinyl versions; they’re also durable. The major drawback to aluminum-frame windows is their metal frame-they conduct heat easily, earning them a high U-value. (Higher is not better here — the higher the U-value, the more heat a frame loses.) Compared with vinyl or wood frames, which fall within the 0.3 to 0.5 range, aluminum frames can have a U-value as high as 2. They also tend to feel cold to the touch and are prone to condensation.

Those drawbacks make aluminum-frame windows suitable only for warm climates where cooling bills are greater than heating bills. If you decide to install aluminum windows, be sure the ones you order are equipped with a thermal break in the frame — usually a strip of plastic or rubber that keeps the inside and outside of the frame separate in order to help limit heat conductivity.

Fiberglass and composite-frame windows are the newest options. Made from materials similar to those on car bumpers, both are strong, maintenance-free and more energy efficient than vinyl. And at a price roughly between vinyl and wood, they’re also affordable.

Owens Corning offers a composite unit called Generations for the replacement market. Marvin produces a line of composite windows called Integrity. Made of Ultrex, a combination of fiberglass and polyester resin, the Marvin units can be painted to suit your taste, something you can’t do with vinyl windows.

As with vinyl windows, look for a uniform color throughout the frame and joints that are heat-welded rather than joined with fasteners. And whichever window you’re considering, don’t go by material alone. Check out the locks, cranks and lifts: they should be easy to use and feel comfortable in your hand. A quality window has quality hardware.

Savings and Strength
As recently as 20 years ago, the windows in most homes held a single pane of glass. But for an average-size house, those same windows today can result in significant losses: Single-glazed windows in a cold-climate house would result in a yearly energy bill of about $800, and in a warm-climate house, the energy bill would be about $850, according to Residential Windows: A Guide to New Technologies and Energy Performance by Carmody, Selkowitz and Heschong. The book reveals that today’s high-tech double glazing would reduce annual energy costs in these same houses to about $450 and $500, respectively.

Most of those savings come from two techniques manufacturers use to make double glazings more efficient: low-e coatings and inert gases that fill the spaces between the panes. Low-e coatings were first developed to stop heat loss; newer coatings also stop heat gain where cooling is the key consideration. These coatings usually add 10 to 15 percent to the cost of a window.

A rating system developed by the National Fenestration Rating Council (NFRC) makes gauging the efficiency of a window quick and easy. A label on each window includes its U-value; its solar heat gain coefficient (SHGC), which tells how much heat it lets in; and its visible light transmittance. If you want to cut energy loss during the heating season, look for windows with low U-values. For optimal cooling, go with units that have a low SHGC but let in plenty of visible light.

You can avoid these ratings comparisons altogether by shopping for windows that carry the Energy Star label. Developed by the U.S. Department of Energy and the Environmental Protection Agency, the program tags the most energy-efficient windows. It also targets requirements to specific climates. Windows that meet these energy requirements are 15 to 40 percent more efficient than those that meet typical building codes.

In cooling-dominated areas, U-values of 0.75 and an SHGC of 0.40 or below are required. In heating-dominated areas, U-values of 0.35 or below are required while there is no SHGC requirement. And in areas with mixed heating and cooling needs, U-values of 0.40 or below and SHGCs of 0.55 or below are required. (The determination for a heating-dominated climate means at least 70 percent of heating and cooling costs go to heating. In a cooling-dominated climate, at least 70 percent of heating and cooling costs go to cooling. In a mixed climate, at least 30 percent of heating and cooling costs go to each.)

Another new program helps ensure that wood, vinyl and aluminum windows meet minimum structural standards. Developed by the American Architectural Manufacturers Association in conjunction with the National Wood Window and Door Association, this nonmandatory program puts windows through their paces with a series of performance tests. Windows that pass the tests are granted a certification sticker.

Choose the Right Style
Choosing a window style that goes with the rest of your house is another crucial concern. The wrong choice can ruin the look of your house and lower resale value. Consider these rules of thumb:
1. Traditional or colonial-style homes look best with small double-hung windows with divided lights-referred to as “six-over-six” or “eight-over-eight” to describe the number of panes in each sash.
2. For modern or contemporary homes, large, metal-frame units are a safe bet.
3. Ranch-style houses often look best with out-swing casement windows that don’t have divided lights.

If you don’t like the window style you’re replacing, look at designs in similar homes. And ask your dealer or contractor to show you how different styles look in their past jobs. Window style is also critical when adding window area to a wall. Install units similar or identical to existing windows in shape and size and gang them together — a better arrangement than installing one large unit that looks out of place.

Yet another concern is where to locate new windows on a wall — something that depends partly on ceiling and floor locations. An easy way to determine placement, according to Crosbie, is to stand outside and line up the top of the new windows with the top of an existing window. Even if the new windows aren’t the same length, a consistent head height will give them a sense of order on the wall.

When shopping, also look at a manufacturer’s entire line of windows. Most companies offer their product lines in different materials, grille designs and sizes. Some also offer windows designed specifically to complement older homes. Finally, walking unprepared into a window showroom or home center can leave you reeling. Some advance planning will help you choose windows that transform your home, save energy and provide years of service.