Do-It-Yourself Savings Project: Install Exterior Storm Windows with Low-E Coating | Department of Energy

Do-It-Yourself Savings Project: Install Exterior Storm Windows with Low-E Coating

Storm window installation is one of the most cost-effective solutions for upgrading energy inefficient existing windows. They’re easy to install and cost a fraction of replacement windows. In fact, installing a low-emissivity (low-e) storm window over a single pane window can lower your utility bill just as much as replacing the window with a new energy code-level window.

Coated with an ultra-thin, virtually invisible layer of metal, low-e windows reflect infrared heat back into the home. This coating improves the window’s insulation ability, in turn lowering your heating and cooling costs. On average, low-e storm windows can save you 10%–30% in heating and cooling costs. This equates to $100–$300 in annual savings, assuming a $1,000 annual heating/cooling bill. Information on energy performance is available for all rated products through the Attachment Energy Rating Council (AERC). Look for storm windows that have the Energy Star label.

After deciding to install a storm window, your first step will be to choose which type is right for your home. All storm windows will make your home more energy-efficient, but you can choose between different materials and coatings, and whether you want to install them on the exterior or interior of the home. We’ll focus on exterior storm windows, which fit on all standard double-hung windows and are the most common type installed by homeowners. Outward-swinging windows require interior storm windows. More information on interior-mounted storm panels be can found at DOE’s Building America Solution Center.

When installing any storm window, there is a slight risk of condensation developing between the existing window and the storm window. To minimize this risk, до installing the storm ensure that the original window is as air tight as possible by caulking the tops and sides (jambs and head), follow the manufacturer’s installation instructions, and use a product that includes weep holes at the bottom of the frame to further reduce any risk of condensation between the storm window and the existing window.

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  • Ensure that the window and adjacent surfaces are dry. Fix any missing glass, rotting wood, broken parts, and water leaks.
  • Get your new storm window measurements.
  • Measure the width between the inside edges of the window casing in three places: at the bottom, top, and middle of window (round down to the nearest 1/8 inch).
  • Measure the height from the top of the window casing to the sill at its highest point (again, round down all measurements to the nearest 1/8 inch).
  • If the horizontal measures differ, use the smallest of the three when ordering a new storm window.


  • Штормовое окно
  • Рулетка
  • Отвертка
  • Шпатель
  • Заткните
  • Монтажный пистолет


1) Position the storm window into the opening to check for proper fit.

Determine the top of the storm window by noting which direction the movable panels (if applicable) operate. Center the storm window in the opening. Ensure that all screw holes land on solid wood.

2) Remove the storm window.

3) Caulk the top and sides of the existing window opening. Do not caulk the bottom sill.

Hold the caulking gun at a 45-degree angle to the edge of the window. Using a “pulling” motion, hold the gun at a consistent angle and slide the tube nozzle along the joint while evenly pressing the trigger of the caulk gun.

4) Reposition the storm window into the opening.

Ensure the top of the storm window is pushed up snugly into the very top of the opening.

5) Secure the storm window to the window frame.

Using your screwdriver and the screws, temporarily secure the top corners of the window.

6) Adjust the expander on the bottom of the storm window.

Typical storm windows will come with a window sill expander, which allows the bottom of the storm window to expand (around ½ inch) to meet the angled sill of the window opening. Use your putty knife to tap down the adjustable expander tight against the windowsill. The expander should make even contact across the bottom sill.

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7) Square up the window unit, and then install the remaining installation screws.

Make sure the gap between the window and the frame is even (the ideal gap is 1/16 inch on each side of the window).

Installation videos and more detailed guidance can also be found at DOE’s Building America Solution Center

Window Film: A Cost Effective Window Retrofit

Window film technology has improved since it was first conceived. Newer films are high-tech products that adhere well and greatly improve an old window’s performance at a modest cost. As this advocate for films suggests, they definitely should have a place at the green retrofit table.-Editor

WHEN IT COMES TO ENERGY EFFICIENCY, windows may be homeowners’ Achilles’ heel. Between 10 percent and 15 percent of the energy a home uses is lost through windows, according to the U.S. Environmental Protection Agency (EPA). Also, windows may be responsible for as much as 25 percent of a home’s heating bill. Nearly 75 percent of existing windows are not energy efficient.


Windows can also have other impacts on a home. The sun’s harmful ultraviolet rays can do major damage to interior furnishings, carpets, flooring and desks. UV rays are responsible for as much as 40 percent of the fading that occurs inside a home.

The obvious solution is to completely replace those old windows with higher performing glass, right?

Maybe. But a more cost-effective and environmentally sound solution might be installing window film on the existing windows, enabling a powerful combination of improvements, including better energy efficiency and reduced UV rays without losing light and views, while preserving furnishings. Consider it “repurposing” your windows instead of buying new ones!

What is window film?

Some people may have a memory of window film as the purple-tinged, bubbly material seen on many cars in the 1970s. Today’s window films are much higher performing and technologically advanced.

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Window film is a flexible product usually made up of multiple layers of coated or chemically treated polyester, often with a lightly metalized layer for better solar properties that can be installed on glass. Films range in thickness from 1-mil to 15-mil. For residential structures, it’s primarily used for retrofit applications to existing windows.

There are literally hundreds of types of window film, but the most common are solar control films, which are designed to help protect a home or commercial building from the harmful effects of the sun including heat, fading, and UV radiation. There are also films that can enhance security, increase privacy or add decorative features to a building.

Window film can reduce the amount of heat transmitted through glass windows or doors, and also help buildings retain heat during the colder months. A home or building’s HVAC system doesn’t have to shoulder as much of the cooling and heating load when the proper window films are installed.

As an added safety benefit, window film can hold the glass shards of a window together if the glass is broken during a storm or man-made incident, preventing flying glass from doing harm, and continuing to offer protection from wind, snow and rain.

Full replacement versus window film installation

While replacing windows is an option, many older windows may actually be of higher quality than the newer windows one may install. Installing films on existing windows is far less intrusive and is done in a very short period of time. In older dwellings and multifamily buildings, it may be possible to achieve similar energy efficiency, at a fraction of the cost, by installing window film on existing windows rather than full replacement.

It is important to take the climate into consideration in making your decision.

Example #1 – Colder Climates

To determine how energy efficient a window is during the winter months, an organization called the National Fenestration Ratings Council has developed a rating called the “U-Factor.” The U-Factor is a measure of the amount of heat that’s allowed to pass through a window, measured in BTUs per square foot, per hour. The lower the U-Factor, the less heat is lost. For example, a window with a U-Factor of 0.5 will lose half of the heat that a window with a U-Factor with 1.0 will lose.

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The least thermal efficient windows have a U-Factor of about 1.3, while the most efficient windows can be as low as 0.2.

As an example of the benefit window film can offer, let’s use the energy analysis report of window film residential performance in California for the International Window Film Association by energy consulting firm ConSol in 2012.

This analysis looked at a standard single pane window with a U-Factor of 1.09, without any film installed. Installing today’s high-performing window films that are designed to limit heat loss could give that window a U-Factor of 0.9. A double-pane window could see a difference in the U-Factor from 0.71 to 0.65.

If the glass is also treated with a “Low-E” (low-emissivity) coating – which improves the thermal efficiency of a window – the U-Factor of that same double-pane window could be as low as 0.55. Many of today’s most advanced window films can be used in conjunction with a Low-E coating, to help further reduce heat loss.

Example #2 – Warmer Climates

In warmer regions, the goal isn’t so much managing heat loss, but minimizing heat gain through windows – which helps reduce the cooling costs. For this purpose, a different standard – called the Solar Heat Gain Coefficient (SHGC) – is used. The SHGC is measured on a scale of 0 to 1. The lower the number, the less heat is emitted through a window into a home.

The same IWFA analysis above uses as an example a single-pane window without any glazing or film, with a SHGC of 0.71. With a high-performing window film designed to reject solar heat, the SHGC could be as low as 0.45. For a double-pane window, the SHGC difference could be from 0.63 to 0.45, without and with window film. With low-E glazing also installed, the SHGC could be as low as 0.2.


As shown in the examples cited above, the installation of window film can make a dramatic difference – either for keeping heat in a home during colder months, or rejecting heat during warmer months. Before you make the decision to replace older windows, consider your specific energy efficiency goals. As noted in the examples above, you can dramatically improve the comfort of a home and energy performance of existing windows by investing in window film, at a fraction of the cost of a complete window replacement.

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An energy audit of a home can help determine the expected energy savings from a professional window film installation. Considering factors such as the local climate, whether the existing windows are structurally sound, and how quickly you’d like to get a return on your investment, will help you decide what energy saving measures will work best for your home.

Jeffery Plummer is the senior vice president of sales and marketing for Madico Window Films based in St. Petersburg, Fla. He can be reached at

Оконные пленки

Homeowners and business owners can employ a number of methods to “green up” their indoor environments to make the interior more comfortable and to lower heating and cooling costs. One method is installing window film. Window film is represented in three general categories. Most familiar to consumers is the tinted cellophane-type material that can be applied temporarily or used as needed, as in glare-reducing retractable shades. It can also be semi-permanent, such as window tint that is applied directly to windows and remains in place. It can also be permanent, such as the product Heat Mirror™, which is different from typical films and tints. Their prices range from fairly inexpensive to very expensive. InterNACHI inspectors can learn more about the different types of window film technology available, along with their performance characteristics, which can be useful when it comes time to make recommendations to their clients following an energy audit.

Window film or tint is available for purchase from hardware stores in long sheet rolls. It’s relatively inexpensive and may be applied directly onto windows by the homeowner or business owner to provide shading without blocking all sunlight. This is the same type of tint found on vehicle windows. Heavy-gauge window film is sometimes applied to windows to keep them from shattering into dangerous shards in case of an impact. Most window films can be cut to fit any size or shape and can be removed with steam or a razor blade and alcohol.

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Heat Mirror™ and low-E coatings are factory-installed and permanent. Heat Mirror™ is a clear, three-layer polyester film that transmits light through insulated glass units (IGUs) while reflecting long-wave infrared energy. It was developed by Southwall Technologies in 1980 to reduce the amount of solar heat transferred into a home or commercial building, increasing the occupants’ comfort and reducing energy costs.

Heat Mirror™ can be mounted inside an insulated glass unit in a variety of configurations (one, two or three coated films, uncoated, or low-E coated glass) to provide energy conservation performance ranging from R-6 to R-20 in order to meet the unique requirements of commercial and residential new construction and renovation. Designations include a two-digit number that represents the amount of light transmitted through the coated film. For example, Heat Mirror™ 22 is designed to block more infrared light than Heat Mirror™ 88.

The polyester film bisects a layer of argon or krypton gas that fills the gap between two glass panes, creating an extra air space that significantly improves the window’s R-value and associated heating and cooling costs. Inspectors and homeowners may become confused regarding the properties of Heat Mirror™ and other green products commonly applied to windows, such as low-E coatings, which also use a reflective layer to reflect infrared energy. Low-E film, however, is made from metal or metal oxide instead of polyester and is physically applied to the glass surface. Unlike Heat Mirror™, a low-E coating does not increase the number of air spaces in an IGU. Debate has persisted for many years concerning which is the better design, with proponents on each side pointing out defects and inefficiencies of the other product. The two designs are sometimes incorporated in the same IGU for additional protection against heat or infrared energy loss.

Amory Lovins is a Colorado resident who pays $0 in energy bills for what may be one of the greenest houses on the planet, according to MSN Money. Heat Mirror™ and other energy-saving features (many of which are covered in InterNACHI’s robust InterNACHI article database) have allowed Lovins to harvest 28 banana crops in his indoor banana jungle without the aid of central heating, despite the fact that his Rocky Mountain estate experiences sub-zero blizzards every winter. There are also plans to install Heat Mirror™ in the Empire State Building’s 6,500 windows as part of the building’s energy retrofit project. According to BusinessWire, the installation of Heat Mirror™ in the windows of New York’s tallest building will decrease energy costs by $400,000, cut solar heat gain in half, and improve the windows’ R-values from R-2 to R-8. Skyscrapers and alpine banana jungles aside, most Heat Mirror™ window film is found in ordinary residential and commercial structures, although it is among the more expensive options available.

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InterNACHI inspectors may be on the lookout for older types of Heat Mirror™ that are prone to discoloration, warping, becoming brittle, and seal failure. One such defect is yellowing, caused by impurities that make their way onto the film before it is sealed within the glass panes. Wrinkling is also a problem in older Heat Mirror™, as you can see in the accompanying photo. These problems have largely been resolved in recent years, as Southwall has corrected manufacturing errors and more closely scrutinized their licensed distributors.

In summary, Heat Mirror™ and other types of window films are designed to reflect solar heat, increase a window’s R-value, and/or provide shading while reducing the building’s energy costs for both heating and cooling, sometimes significantly, depending on the product. InterNACHI inspectors who perform energy audits can help their clients with recommendations on the most appropriate choices for the application and budget.

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