Step 1: Test all mechanical parts to be sure the windows open and close smoothly
Windows are one of the most expensive features of your home, and you'll be disappointed if they're drafty, don't open and shut easily, or break down after a few years. Visit several window dealers and home centers so you can test firsthand and compare as many types and brands of windows as possible.
The cranks on casement windows should turn easily without binding or catching (Photo 1), and the locking latch should pull the window tightly and evenly against the weatherstripping from top to bottom. Double-hung windows should slide snugly in their tracks, yet not bind so that it's a strain to lift and lower them. Sliding windows should glide on their tracks without too much resistance.
Chances are you'll see and feel a significant difference between lower- and higher-priced windows. More-expensive windows generally have heavier-duty, more-durable hardware and better design, making them operate more smoothly. They’re usually a better investment.
For easy cleaning, make sure you can reach all glass surfaces. Test the tilt-out sash systems on double-hung windows (Photo 2). Remove both the upper and the lower sashes. If you can't get them out fairly easily, you'll have to climb a ladder to reach them—and you probably won't clean them often.
Crank casement windows all the way to be sure you can reach out and clean the exterior glass from the inside. Some systems have a release that allows you to rotate the glass for easier cleaning.
Step 2: Read the energy performance labels and compare the different glass options
Windows account for about 22 percent of the heating and cooling losses in the average home. At a minimum, buy windows with the Energy Star label as shown to be assured of decent energy savings. And consider windows with even higher performance; they won't save you a whole lot more on utility bills (yet!) but can make your home a whole lot more comfortable. They'll reduce cool drafts and condensation (see Step 4) in cold weather and keep rooms from overheating in hot weather.
To compare windows, read the NFRC (National Fenestration Rating Council) energy-ratings label that’s pasted on most units (Photo 1). Look for a low “U-factor” first. (Unlike R-value, the lower the U-factor, the better.) This is the rate of heat transfer through the window—glass and sash combined. Higher-performance windows have a lower heat transfer rate, making them more energy efficient, less drafty and less prone to condensation. Double-pane windows with clear glass generally have a U-factor of about .40. Adding a low-e coating and argon gas to the space between the panes lowers the U-factor to about .35 (about a 15 percent improvement). And triple glazing (three panes, Photo 2) lowers the U-factor to about .27. Windows with a low U-factor are ideal for all regions. Note: For a true comparison, you must check the labels for windows that are about the same size.
To control overheating from direct sunlight, look for a lower Solar Heat Gain Coefficient (SHGC). The number roughly represents the percentage of the sun's heat that comes through the glass. Low-e coatings on the glass can block most of that heat. These coatings are ideal in warm regions where the windows receive direct sunlight. They're valuable in colder regions as well to block the late afternoon summer sun on west-facing windows. Tints also block the heat of the sun, but they will obscure your view. Compare another number, the Visible Transmittance, to make sure your rooms remain light and bright and you retain a good view. A .50 value is good; a higher value is better.
Chances are that the windows you'll see in a showroom will have similar ratings, indicating an adequate glass option for your region, but usually not the best. You'll have to ask about other options. They'll cost a bit more, but they're usually worth it. One good Internet source to compare energy ratings of various windows (and brands) for your region is www.efficientwindows.org.
Step 3: Look for a long glass seal warranty
Double-pane insulating glass is great for comfort, convenience and energy efficiency, but it has one weakness. If the seal between the two panes deteriorates, moisture will creep in and the glass inside will fog up (Photo 1). There is no fix for this. You have to replace the glass, typically costing $50 and up, plus labor. Manufacturers know approximately how long their seals will last (the failure rate) and plan their warranties accordingly. Don't buy a window with less than a 10-year glass seal warranty. Better warranties will go up to 20 years.
Unfortunately, glass replacement is rarely easy. Check the warranty (save your receipts!) to see if it covers just the new glass, an entire new sash—glass plus the wood, vinyl or metal frame surrounding it—and/or the replacement labor. Better warranties transfer to new owners, so if you recently bought a home with fogged windows, you might be in luck. Check with the manufacturer.
Tip: The window brand and date of glass manufacture is usually etched into a corner of the glass or the edge spacer (Photo 2). If you have trouble finding it, call a window repair expert (search “Window Repair” online or in your yellow pages).
Step 4: Bugged by condensation? Look for windows with “warm” edge spacers
Persistent interior condensation in cold weather makes the air inside your house drier and causes sash deterioration. It's an irritating problem, because you often have to further lower your indoor humidity to an uncomfortable level to protect your window sash. Windows with a low U-factor (rate of heat transmission) pay off here, because they cause less condensation. However, even high-performance windows may have a cold spot around the perimeter of the glass because of the metal edge spacer, the rigid tube that separates the two glass panes. That's where you'll see condensation first occur. Some manufacturers address this detail by installing “warm” edge spacers, that is, spacers that transfer less heat. Finding this information can be difficult. The NFRC label might include a condensation rating, but it's an optional category that few manufacturers use. Ask the sales staff or call the manufacturer to find out if it uses warm edge spacers.
Step 5: Check the exterior fit on replacement windows
Your new windows may fit nicely into the old rough opening and look great from the inside, but they may not look good from the outside. Usually you want the exterior dimensions of the new window frame to fairly closely match the old so that the exterior trim remains the same (photo). If the trim sizes change and look unbalanced, the windows will look odd. You'll have to spend several extra hours per window cutting siding and making new trim, or pay a carpenter an extra $100 to $200 per window to make the corrections. The difficulty and cost go way up if your exterior is stucco or brick.
Since new windows have to be ordered, you won't have the opportunity to measure the new unit itself. However, the window catalog usually lists “unit” dimensions, which should be the actual outside dimensions. The catalog may include cross-sectional details of the top, bottom and sides of the unit so you can see how it fits into the opening. Sometimes one model or brand will fit better than another. Some manufacturers will make windows any size you want, which may be a simpler and less costly solution if you have a masonry or stucco exterior.
Step 6: Make sure you can find replacement parts
Depending on how much you move them, such parts as crank arms, counterweight springs and weatherstripping will eventually wear out. Replacing these parts is usually fairly easy, but finding the replacement parts, especially 20 years from now, may not be so easy. Many key parts are not standardized; they're unique to the brand and model of window. So ask if the manufacturer makes spare parts readily available. This is one advantage of buying from manufacturers who have been in business a long time. They'll probably be available to supply spare parts years later. If you're lucky, you can find parts through aftermarket sources. One source is Blaine Window (www.blainewindow.com).