What to Know Before Replacing Your Windows

Window shopping 

It’s easy to be overwhelmed by all the choices you have to make. Here’s a guide to help you through the buying process 

WINDOWS DO SO MUCH FOR A HOUSE. They let in the light that brightens our rooms; they shut out the bad weather, and, when open, they give us a welcome flood of fresh air. Without windows, our homes would be as dark and depressing as caves. 

But maybe your windows aren’t doing their job very well anymore—chilling you with cold drafts in the winter and saddling you with high AC bills in the summer. Or maybe they’re allowing water to dribble in, inviting rot and structural repairs. Perhaps the insulated glass is foggy or the sashes are stuck. If any of these things are happening, it may be time to invest in new, energy-efficient windows, ones that look as good or better than the ones you have. 

This is not a decision to be taken lightly. Windows are prominent features of a facade, and new units should be true to a house’s style and history. And there’s a daunting number of choices to be made, from what materials to choose, how the window is installed, how it operates, and the pattern of the bars dividing the glass. Using this booklet, you’ll be able to make sense of the options and learn how to compare products so that you can talk knowledgeably with dealers and installers. Being informed is the best way to reach your goal: to get the best-looking, best- performing windows—ones that meet your needs and fit your budget. 



While a well-made window can easily last 50 years or more, manufacturers usually offer warranties of 10 years on hardware and workmanship and 20 years on the seals that keep insulating glass from fogging. Some makers will even cover exterior-finish failures within a specified time span. 


Leave this to a pro who has experience assessing and measuring a window opening and knows how to properly install replacement windows. 


Energy Star–rated windows can cut heating and cooling costs from 11 to 37 percent, depending on the type of windows being replaced and your climate zone. 

These fiberglass insert windows were installed from the inside so that the existing trim could stay in place. 

Replacement Options 

  1. Full frame This unit offers the most styles and highest energy efficiency. Because it’s installed from the outside, the same as in new construction, all the existing window’s exterior trim must be removed and some siding may need to be replaced. Doing so allows the framing, flashing, and insulation around each opening to be inspected and upgraded, but it also pushes up the installation cost. 
  2. Insert This unit is installed from the inside, where it fits within the existing window frame; the trim remains untouched. Because an insert goes in so quickly, its total cost usually ends up being less than that of a full-frame replacement. Keep in mind that an insert’s frame reduces the size of the window opening— and the amount of light it lets in—by about 1 inch on all sides. Also, an insert may not be an option if the existing window frame is out-of-square or structurally unsound. 

Choose your style 

The way a window operates should be in keeping with the style of house you have.


    The most popular window type in the U.S.A., and the most appropriate type for traditional house styles, it has two sashes that slide up and down. (On single-hungs, only the lower sash moves.) The screen mounts on the outside. When open, the sashes cover at least half the window opening.


    Its hinged sash swings out like a door, so there’s nothing to block airflow through the opening. Seals tightly to its jamb, making it one of the best types for keeping out the weather. Operates by hand or by turning a crank. If left open, the sash is vulnerable to wind and rain. Most appropriate on contemporary and Prairie-style homes. The screen mounts on the inside. 

  3. SLIDER 

    Like a double-hung window placed on its side, the sashes slide on horizontal tracks— there’s no lifting. Best for contemporary house designs. The screen mounts to the outside. The lower tracks require regular cleaning. As with a double-hung, the sashes always cover at least half the window opening. 


    It’s like a casement mounted on its side. An awning window (shown) is hinged at the top and swings out, so you can leave it open when it rains. The screen is on the inside. A hopper window has bottom hinges and swings in. The screen is on the outside. Both types seal well, and with the right muntin configuration they can look good on either traditional or modern houses. 


    Common in Europe, this window has special hardware that allows it to tilt in like a hopper or pivot in like a door, depending on which way you turn the handle. The screen mounts outside. It does a superb job of sealing out the weather, but it’s the most expensive window type. 


There’s no sash to open, so it lets in only light, not air. That makes it less expensive and more energy efficient than comparable windows with sashes. Best for inaccessible areas, such as gable peaks, or as architectural accents because it can be crafted in so many sizes and shapes.


Double-pane: Compared with single-pane windows, this type is up to 37 percent better at preventing heat transfer, so interiors stay warmer in winter and cooler in summer. The glass is also less susceptible to condensation.

Triple-pane: Adding a third layer of glass cuts heat transfer by another 30 percent, making this the best barrier against cold and condensation. A good choice for north-facing walls because three panes cut down on the amount of light and solar heat a window lets in. 

Laminated: An invisible layer of plastic sandwiched between two sheets of glass creates a pane that’s virtually unbreakable and can foil intruders, block sound, and withstand earthquakes and hurricanes. 


Your choice determines a window’s longevity, performance, and looks 

  1. WOOD Long a traditional favorite, it’s attractive, a decent insulator, and easy to repair. There’s virtually no limit to how it can be customized. Too bad it’s vulnerable to water. Attentive maintenance is the key to how long this window lasts. May be the only option in historic neighborhoods. 
  2. CLAD-WOOD This is a wood window covered by an outside layer of vinyl or metal, usually aluminum, that virtually eliminates maintenance. Metal cladding is more durable by far. This window shows off wood’s aesthetic qualities on the inside while making use of its insulating properties. 
  3. FIBERGLASS This mix of spun-glass fiber and polyester resin is rigid, strong, impervious to water, and as good an insulator as solid wood. Some manufacturers offer a wood lining on the interior. About as maintenance free a window as you can get, for less than a comparable wood unit. The downside? A limited number of design choices. 
  4. VINYL It’s inexpensive, to be sure, but slowly becomes brittle with age. The frame isn’t stiff, doesn’t insulate well, can’t be repaired, and looks nothing like traditional wood. 
  5. ALUMINUM OR STEEL It’s low-maintenance but suitable only for mild climates because of how easily it carries heat outside in the winter and inside in the summer.

Shapes & Patterns

A crown on the casing and ogee lugs on the upper sash elevate the aesthetics of this six-over-one double hung. (Six-over-one is shorthand for the number of panes in the upper and lower sashes, respectively.)
Unlike the up-and down symmetry of a double-hung, the upper sash is one third the size of the lower one and usually fixed. Fits nicely on Craftsman style houses. 
This arrangement of tiny panes around a big central pane originated in the Victorian era. Often, the panes were colored to create a stained-glass look at a low price. 
The bars in this casement window echo the shape of the sash
The curved frame on this double-hung would fit nicely in the confines of a dormer or gable peak.
This playful take on a four-over-two double-hung features a circular fifth pane in the center of the upper sash—just one example of the custom options available in wood.


4 Ways to dress up Insulated Glass

Grille in Glass
Metal spacers between the panes lack authenticity, but the glass is easy to clean. Most efficient if the grille doesn’t touch the glass
Removable Grille
A wood grille resting against the pane’s inside surface pops off the edge of the sash when the glass needs cleaning, then pops back in.
Simulated Divided Light (SDL)
Wood bars affixed to the sash cover the pane inside and out. Looks more authentic than a grille, but slows down glass cleaning.
SDL With Grille in Glass
Combines metal spacers matched with fixed bars inside and out to re-create the look of a true divided lite window with actual muntins.

Look for the Label

To know how effectively a window halts heat loss or reflects the sun’s heat, among other things, consult a label like the one at right. It contains test results from the National Fenestration Rating Council (NFRC), an independent organization, that you can use to quickly compare the performance of different windows. Not all windows are subject to NFRC scrutiny, so this label is your assurance that a unit meets the local energy code. Here’s the key information, deciphered. NOTE Some labels also report the air leakage through a unit in cubic feet per minute per square foot. Look for 0.3 or less


A window suited to Miami won’t work in Minneapolis 

THE MINIMUM ENERGY EFFICIENCY STANDARDS set by the federal government for new windows are not uniform across the country; the standards change based on climate zone. Using the information on this map and on the printed label, you can quickly determine which windows are best for your region. Keep in mind that these are minimum requirements—don’t overlook windows that offer even better performance numbers.


What to look for in high performance window glass 

  1. Low-e coatings These transparent, micron-thin layers of metal reflect heat either toward the interior (in cold climates) or toward the exterior (in warm ones), depending on the glass surface they’re fused to. They can reduce heat loss (or gain) by as much as 35 percent.* 
  2. Inert gasesAir trapped between panes insulates fairly well, but if a gas such as argon is used instead, performance improves by 16 percent.** Xenon and krypton insulate even better than argon. 
  3. Warm-edge spacers Standard aluminum spacers conduct lots of heat through the edges of doublepane glass. Nonmetallic, warm edge spacers bring those losses down by 10 percent** and make it more difficult for condensation to form on inside panes.

*Source: U.S. Dept. of Energy; energy.gov
**Source: Cardinal Glass; cardinalcorp.com