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Windows and Doors


Windows provide light, ventilation, fire escape, and a view. Yet they create weak link in your home's thermal boundary, because they can't be insulated as well as the walls in which they are installed. Windows also allow some air leakage into your home.

Fortunately, you can have plenty of windows and still have an efficient home. You just need to choose the right types and install them properly.

Learn here how to evaluate the energy performance of your existing windows and decide whether to improve or replace them.

This section also shows you how to weather-strip doors to slow air leakage, and how to choose doors for replacement.

Evaluate Your Windows and Doors

You should have at least two panes of glass on all your windows. Windows are always the weakest point in your home's thermal boundary. If you have single-pane windows, you can cut your window energy loss in half by installing either storm windows or insulated double-pane glass.

Your windows should be water tight at the exterior. The cost of window replacement is often difficult to justify based solely on energy savings. However, if the old windows are worn out such that water leaks into your home, replacement or repair should be top priority in order to protect your home from water damage.

Insulated window coverings such as curtains can cut the heat loss through your windows by half or more. Light curtains, mini-blinds, and roller shades are less effective.

You can also reduce the cost of air conditioning substantially by shading your windows with curtains, roller shades, awnings, or trees.

  • Window Basics

    The average home has twenty to thirty windows, totalling some 12 to 25 percent of the wall area. Since even the most advanced windows have an R-value of between R-3 and R-6, windows are by far the weakest link in your home's thermal boundary. It is for this reason that window improvement is so worthwhile.

  • Understanding Window Ratings

    If you are purchasing new windows, pay close attention to the ratings published by the National Fenestration Rating Council (NFRC). Most windows carry labels with the NFRC ratings on them. Don't buy windows unless they display this label.

  • Improve or Replace

    Before you make the decision to replace your windows, be sure to do some research so you know about the entire range of choices. New windows include many convenient features and choices of styles, but if you're interested in improving the efficiency of your home, you should do some careful analysis before committing your money to buying new windows.

  • Storm Windows

    Installing storm windows is often more cost-effective than installing new windows. The simple reason is cost. Storm windows can be installed on either the inside or outside of the home. Storm windows can usually be purchased and installed for $8 to $15 per square foot, less than a quarter the cost of new windows.

  • Window Repair and Retrofit

    If you are considering spending $500 to $1200 per windows for the installation of replacement windows, why not consider instead spending $100 to $500 repairing or improving your existing windows? You'll often get almost the same results in energy savings, and with much less expense.

  • Insulating Shades and Draperies

    Whether you have your ideal windows in place yet or not, you can make changes to the windows treatment that will affect your energy consumption. Insulating shades and draperies can be effective for insulating shades and improving comfort indoors if residents open and close them at the appropriate time. Shades and draperies are expensive and require many years to return the investment, but they cost considerably less per square foot than a new window.

  • Install Heat Mirror Insulating Glass

    Insulating glass units will significantly cut the amount of energy used in the home. The Heat Mirror insulating glass unit from Southwall Technologies is a solar reflective film applied to a window's interior that prevents the loss of radiant heat through the window at least three times more efficiently than double-pane glass. With an R value (the measure of thermal resistance used in heat transfer) of 7.7, the inside surface of the home's Heat Mirror insulating glass remains close to room air temperature. To put that into context, the R value of double pane glass window is R-2, while a double-pane glass window or skylight with a Low-E coating, is R-3, and closed-cell polyurethane spray foam has a value between R-5.5 to R-6.5.

  • Window Replacement

    Once you've chosen the right window, you still have to ensure installation is done carefully to avoid future problems. The most important consideration for windows replacement is making the installation water tight. Preventing air leakage around the frame and sizing the windows correctly are also essential.

  • Improving Efficiency of Doors

    Doors are expensive to replace, and they have a long payback period compared to the other energy conservation measures. But since doors offer many non-energy benefits such as security, weatherproofing, and aesthetics, they are often included in energy retrofit plans.

  • Summing Up

    Windows and doors are critical components in your home's thermal boundary. They are expensive, and replacement can consume a large part of your home improvement budget. Yet some of the simplest repairs and upgrades are the most effective energy conservation techniques.

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