How to Insulate Windows

A worker insulates a window on a new construction building
In the colder parts of the United States, anywhere from 15 to 35 percent of heat loss in wintertime can be attributed to poorly insulated windows.
­ iStockphoto/Michael Walker

­As the weather gets colder, you might start to notice a draft entering your bedrooms and kitchens from the windowsills. Placing a hand near the window on a windy night can reveal -- brrr! -- the source of the draft. Even if the cold air isn't leaking in through gaps, the window itself can make the indoor air cooler. Those old single-pane windows provide only a thin glass barrier against the elements. Windows can have a significant impact on home heating costs: In the colder parts of the United States, anywhere from 15 to 35 percent of heat loss in wintertime can be attributed to poorly insulated windows [source: Shurcliff].

In other areas of the country, like the Sun Belt, the major concern is keeping homes cool in the warmer months. The summer sun penetrates windows and increases the ambient temperature in your home, forcing air conditioners to work harder. The result -- higher electric bills. So, short of blocking all natural light from your home, what can you do to save on those bills?


­The solution to both problems is insulating your windows. A sturdier barrier between the outdoor and indoor environments will keep your home cooler in the summer and warmer in the winter.

There are many ways to insulate windows. The methods range from simple to complicated, practically free to fairly expensive, low-tech to high-tech. Adding storm windows -- or doubl­e- or triple-glazed high-performance windows - is certainly one way to go. Thermal shades, or regular drapes of the right size and thickness, can do a good job, but that may mean giving up daylight and visibility. Several companies market insulating panels and other products that you can install on the indoor side of windows. And if you're really on a low budget, don't forget the benefits of bubble wrap!

If you're ready to begin learning how to insulate windows, move onto the next section.


Preparations for Insulating Windows

It's sensible to begin by diagnosing the situation. Instead of giving your home a complete energy inspection, play Sherlock Holmes and pinpoint the most critical areas for heat loss. For example, a chronically cold kitchen with large north-facing picture windows is probably a good place to start. Assess where the heat loss is coming from: Is there an obvious draft from the sills or sashes? If so, weather-stripping may be the best line of defense. Give some attention to what type of windows you're thinking of insulating. Perhaps part of the problem is a lack of insulation at the window jambs -- where the window meets the wall -- or behind moldings.

Before you select a method of insulation from the available options, you should also consider your objectives. Obviously, temperature regulation is a primary objective, but how much do you need to increase the insulation value, and what tradeoffs are you willing to make? Will you compromise the view, limit the influx of light or block access to the window? Are you looking for a year-round form of insulation, or will a seasonal fix suffice?


Of course, you'll need to factor in cost. Some remedies can be obtained for modest costs, such as rubber or foam weather-stripping or plastic sheeting. More lasting solutions, such as spraying or inserting insulation in the jambs, will cost more money and may require the help of a contractor or handy person -- but they may prove a worthy investment in the long run. You also may want to think about aesthetics: Tasteful window treatments or homemade thermal shades certainly make a different kind of statement than caulk, foam and vinyl.

After you've considered all these matters, it's time to get to work. Make careful measurements of the windowpanes, casings and frames. If you plan to mount shades or blinds, decide whether insulating inside or outside the casing best fits your needs, remembering that insulating the inside will more efficiently reduce airflow [source: Pandolfi].

Let's move on to learn about what steps to take and with what kinds of tools to use along the way.


Steps and Tools for Insulating Windows

Not every insulation project follows the same process. Here are a few basic techniques you'll need to know an­d tools you'll need to have handy when insulating your windows.

  • Plastic insulating film. It's easy to find inexpensive window insulation kits at hardware or home-repair stores. The kits come with a large sheet of plastic film and a quantity of double-sided adhesive tape. Stick the tape around the window frame on all four sides, then mount the film on the tape so it completely covers the window. The film will block all access to the window, so if the window has Venetian blinds, cut a little hole while mounting the film and sneak the control rod through so the blinds can be opened and closed. Cut the excess film away with a knife or scissors. The last tool needed for this job is a hair dryer: Blow hot air at the film so it tightens and makes a firm seal with no wrinkles.
  • Insulating drapes. The key to using drapes as window insulation isn't the heaviness of the material but the tightness of the seal. The objective is to prevent the room air from circulating into the space behind the curtain. Weights, magnets, Velcro, snaps or staples can be used to make sure no space is left between the drapes and the window frame, windowsill or floor. You can insert effective thermal shades while leaving existing drapes or shutters in place. Do-it-yourselfers can make them at a fraction of the retail cost.
  • Insulating at window sashes. The challenge of this job is prying off the molding that surrounds the window frame. Once that's done, it's relatively simple to measure a piece of rigid insulating foam to fit into the space between the window jamb and the wall, and spray a substance such as expanding polyurethane into the jamb itself.

In the next section, we'll find out how your hard work will pay off!


Benefits of Insulating Windows

As we mentioned, windows can be a costly feature of a home, accounting for substantial heat loss in cold weather and heat gain in warm weather. Single-pane windows, found in nearly 50 percent of American homes, are the most extreme in terms of energy-inefficiency [source: Money Matters 101]. Improving the energy infrastructure of your home will reduce home heating and cooling costs and help reduce fossil fuel consumption, slowing down the carbon emissions that are disrupting the global climate.

Heat loss through windows takes place in four distinct ways:


  • Air leaks directly in and out from gaps along the edges (infiltration).
  • Heat passes through the window glass (conduction).
  • Heat energy flows from a warm object toward any cooler object nearby until equilibrium is achieved (radiation). This can cause up to 65 percent of the heat loss from your home.
  • Because heat rises and cool air sinks because of their different relative densities, the cold air at the interior surface of an icy windowpane flows toward the floor, sucking more air behind it toward the window (convection). This movement eventually causes the overall room temperature to drop. This is why it's so important to cut off the flow of air in the vicinity of the window [source: Brighthub].

Effective window insulation prevents heat loss and also helps regulate the surface temperature of the interior glass. Without significant heat loss through leakage or convective airflow, insulated windows ensure an even temperature throughout the interior of the home, increasing energy efficiency. They also make it possible for heated homes to maintain a higher humidity level, and thus better air quality, with a reduced risk of condensation on the windows.

Are you convinced that any effort to insulate your windows is worthwhile and saves money and energy? If you need more convincing, check out the links on the next page.


Lots More Information

Related HowStuffWorks Articles


  • 00orange00. "Insulating Your Windows." (Accessed 02/21/2009)
  • AllSands. "How to Insulate Windows." (Accessed 02/20/2009)
  • Build It Solar. "Bubble Wrap Window Insulation." (Accessed 02/20/2009)
  • Hughes, Eric. "How 2 insulate windows." (Accessed 02/20/2009)
  • Money Matters 101. "Money-Saving Tips: Windows." (Accessed 02/20/2009)
  • Mother Earth News. "The Homemade Thermal Shade." Mother Earth News, November-December 1983. (Accessed 02/21/2009)
  • Pandolfi, Keith. "Drape Away Drafts." This Old House magazine. (Accessed 02/21/2009),,20253692,00.html
  • Serious Windows. "Fiberglass Windows Deliver the Highest Levels of Comfort and Energy Efficiency." (Accessed 02/20/2009)
  • Shurcliff, William. Thermal Shutters and Shades (Brick House Publishing, 1980), p.2. (Accessed 02/21/2009)
  • Silva, Tom. "How to Insulate a Window with Sash Weights." This Old House television (Accessed 02/20/2009),,20051453,00.html