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How to Buy Replacement Windows

By: Carl Laron on August 17, 2017

Styles of replacement windows

Once you narrow down what type of window you need (wood, vinyl, etc.), you'll want to choose styles. The simplest course is to stick with the same style as your old windows, but if you're doing a gut renovation, new construction, or upgrading very old windows, you have more choices available.

There are several replacement window types available, including these common styles:

  • Single- and double-hung windows are the most common kind of replacement window. Double-hung windows have two sashes that move up and down within the overall frame (a sash is the glass and the frame immediately around it). Single-hung windows have only one moveable sash, usually the lower one (the other is fixed). Most new double- or single-hung windows have sashes that tilt inward to make it easier to clean the exterior.
  • Casement windows are hinged on one side and usually swing out when you open them (often with a crank). They provide great ventilation and are easy to clean, but experts say they are not a good choice for dwellings that front high-traffic areas (like a city sidewalk), as they can pose a hazard to pedestrians. Screens can be placed only on the inside of the window.
  • Awning windows are hinged at the top and open out from the bottom. Unlike casement windows, they're good at keeping out rain when they're open. Screens must be placed on the inside. Although older awning windows tended to leak, new windows are fairly airtight and available with either single- or double-paned glass.
  • Sliding windows have sashes that slide back and forth horizontally, rather than up and down vertically, much like sliding glass patio doors. Usually one side is fixed, while the other one slides to open, but sliding windows where both sides can move are also available.
  • Fixed windows don't open; a picture window is an example. These replacement windows are airtight, making them energy efficient; the obvious trade-off is that you can't open them for ventilation. For very large openings, a fixed window may be installed in combination with flanking slider, single hung or double hung windows.

No matter what style and frame material you choose, you will want to buy a well-built replacement window. Experts suggest looking for replacement windows that have been certified by the National Fenestration Rating Council (NFRC) and the American Architectural Manufacturers Association (AAMA). The NFRC rates energy efficiency, while the AAMA certifies the quality of a window's materials and construction.

Windows and energy efficiency

The National Fenestration Rating Council conducts laboratory tests to determine how well a replacement window keeps heat in and cold air out. An NFRC-certified window will carry a label that outlines how energy-efficient the window is, based on the following criteria:

  • U-factor is a measure of how well the window as a whole -- glass and frame -- prevents heat from escaping; the lower the number, the better. Most U-factors are between 0.20 and 1.20. If you live in a cooler climate, experts say, look for a U-factor lower than 0.35.
  • R Value (R-factor) is a measure of a material's resistance to heat transfer through conduction, usually applied to the insulation in walls or attics. It's the reverse of U-factor; the higher the R Value, the better. However, according to the NFRC, heat transfer through windows involves not only conduction but also convection (air flow) and solar radiation (heat), which the R-factor rating does not take into account.
  • Solar heat gain coefficient (SHGC) tells you how well the window blocks heat from the sun, measured in terms of what percentage of the sunlight hitting your windows enters your house as solar heat. The scale is from 0 to 1; the lower the number, the less solar heat will enter your house. If you live in a hot climate, according to most experts, you should look for an SHGC of 0.30 or less.

Some NFRC labels also carry ratings for air leakage, water leakage and/or condensation resistance. These ratings are optional for NFRC certification, but local building codes may require them. The NRFC website also offers more information about these ratings.

Energy-Star requirements for windows

According to the Energy Star website, qualification is determined by the NFRC U-factor and SHGC ratings. The windows with the highest ratings are further distinguished with a Most Efficient award. To find out what Energy Star climate zone you're in and to learn more about Energy Star requirements, see the Energy Star website.

If a window is Energy Star-qualified, it has been certified by the NFRC, so there's no need to check for an NFRC label, although additional information may also be found on the label.

State and federal programs sometimes offer incentives to purchase energy-efficient windows, doors and skylights. The Database of State Incentives for Renewables and Efficiency is a good place to search for incentives in your state, as well as information about federal programs.

Is it cost-efficient to replace your windows to reduce energy costs? This depends largely on the condition of your existing windows, experts say. If your windows are old, leaky or damaged, installing replacement windows is more likely to save you money in the long run than if you're replacing windows that are just a few years old and in good condition. EnergyStar.gov estimates that you will save an average of 12 percent on energy costs if you install Energy Star-qualified windows. If you're renovating your home with the intent of selling it, replacement windows may increase the value of your home, depending on what type you choose, but per the 2017 Cost vs Value survey by Remodeling magazine might not return the full cost of the project. If you are considering replacement windows for a home you are planning to sell, talk to your real estate agent first and ask if they think doing so will be a worthy investment.

What kind of replacement window glass should you choose?

Experts say it's important to choose the best kind of replacement window glass for your climate. The NFRC label on a window includes information about the glass, and retailers and contractors use the same terminology, so it's helpful to be familiar with it.

  • Double-paned (double-glazed) windows are the standard these days; they have two layered panes of glass. The air in the space between the panes serves as insulation, since glass itself is not a good insulator.
  • Triple-glazed windows have three layered panes and provide even more insulation.
  • Gas-filled windows are double- or triple-paned and have an inert gas like argon or krypton filling the space between the panes of glass; the gas provides better insulation than just a layer of air does. The NFRC label will list what type of gas in used.
  • Warm-edge spacers (sometimes called warm-edge technology) hold the panes of glass in a double- or triple-paned window apart. They are made of a material that reduces heat transfer and thus improves insulation, such as foam or neoprene.
  • Low-E (low-emissivity) glass is coated with a virtually transparent metal film that reflects radiant heat. Low-E coatings reflect radiant heat off the inside of the windows and back into the house to help keep it warm in the winter. Most low-E coatings also reflect some of the sun's heat off the outside of the windows, limiting how much of it enters the house as solar heat gain.
  • Low-E 2, low-E 3 glass has two layers of low-E coating, while low-E 3 glass has three layers. Some low-E coatings also block UV rays to prevent furniture or other objects in the house from fading. Tinted glass is another method used to prevent fading, but it also reduces the amount of light coming into a room.
  • High-performance glazing is glass that has several features designed to make it more energy efficient, such as two or three low-E gas-filled panes with warm-edge spacers.
  • Visible transmittance measures how much visible light comes through a window on a scale of 0 to 1. This information should be included on the NFRC label. The higher the number, the more light you'll get. Some coatings or tints may reduce the amount of light.

Can you install replacement windows yourself?

The answer to this question depends on whether you plan to replace the entire window or the sashes only. You will need to replace the entire window -- frame, trim and all -- if an existing window is damaged, and experts say that this is usually a job for a professional. The new window will be more energy-efficient than a window with only the sashes replaced, since it will have new flashing, sealants, caulking and insulation. However, this is the most expensive method of window replacement if you also incur labor costs.

If you are replacing only the window sashes, you have two options. The first, a sash replacement kit, is the least expensive option, according to Fine Homebuilding magazine; you simply remove the old sashes, install new jamb liners and insert the new sashes. The second option is what is referred to as a sash-and-frame unit or an insert -- or, more commonly, a replacement window. This consists of the sashes with a thin frame around them that fits inside the existing window frame. This is the easiest option, according to Fine Homebuilding magazine, and you can judge the energy efficiency better than with option one, since the NFRC will have rated the entire frame-and-sash unit and not just the sashes.

Renovation experts say that even just replacing your window sashes is not an easy job -- especially if you're inexperienced. However, if you decide to try it, some of the websites included in the Our Sources section of this buyer's guide offer step-by-step instructions on how to install a sash replacement kit or a replacement window.

Hiring an installer

According to ConsumerReports.org, many major window manufacturers train and certify their own installers, so it's possible to find a contractor who can both sell and install your replacement windows. This could make things easier if problems arise at some point in the process. ConsumerReports.org also advises that you hire an installer who is certified by the American Window and Door Institute or InstallationMasters. Recommendations from friends and neighbors, or an online resource that offers feedback from others in your area, can also be helpful. Sites such as Angie's List and HomeAdvisor.com (see Our Sources) have databases of local installers with verified reviews from the installers' customers.

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