Storm Windows

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Interior storm windows improved the energy efficiency of a daycare center with windows on the north elevation.
Larry Kinney, Synergistic Building Technologies

Replacing single-pane windows with double-pane windows that have high-performance glass may be cost effective, but you could also consider installing exterior storm windows. Storm windows will produce similar savings at a far lower initial cost. Some types of storm windows are also a good option for those living in apartments. Storm windows can help reduce air movement into and out of existing windows, helping to improve comfort and reduce heating and cooling costs.

Low-E Storm Windows

Storm windows with a low-e coating reflect heat back inside the house during the winter and reflect it outside during the summer, keeping the home more comfortable.

Older storm windows were typically just clear glass, but newer low-e models have a low-e coating that lowers the emissivity of the glass and reduces heat transmission through the storm window. Uncoated glass typically has an emissivity of around 0.84, while low-e coated glass can have an emissivity of 0.16 or lower. Learn more about energy performance ratings.

New low-e storm window designs can be operable or fixed in place and reduce air leakage more than some older storm window designs.

In heating‐dominated climates in north/central zones, low‐e insulating storm panels (both interior and exterior) and insulating cellular shades are effective at reducing heat loss and heating and cooling costs.

In warmer climates, solar control low-e storm windows will likely be more effective for energy savings.

Benefits of Low-e Storm Windows:

  • Costs about one-quarter of complete window replacement[CA1] 
  • Aesthetically pleasing
  • Operable
  • Reduces drafts and increases comfort
  • Reduces noise
  • Similar energy savings as full window replacement
  • Reflect radiant heat 35% better than clear glass storm windows
  • Act as an air sealing measure and can reduce overall home air leakage by 10%
  • Payback of 5-7 years

Low-e exterior or interior storm windows can save you 12%–33% on heating and cooling costs, depending on the type of window already installed in the home.

Interior vs. Exterior

Storm windows are available for most types of windows. They can be installed on the interior or exterior of the primary window.

For the most part, interior storm windows offer greater convenience than exterior storm windows. They're easier to install and remove; they require less maintenance because they're not exposed to the elements; and, because they seal tightly to the primary window, they're more effective at reducing air infiltration.

Interior storm windows also are often the best choice for apartments and houses with more than one floor. If you can afford exterior storm windows, you can probably afford some newer, more energy-efficient windows, which will be a better investment.

Materials

Materials used for storm windows range from inexpensive plastic sheets or films designed for one heating season to triple-track glass units with low-emissivity coatings that offer many years of use.

Glazing

Mid-priced storm windows may use glass, plastic panels, or special plastic sheets that have specific optical qualities. Those made of polycarbonate plastic or laminated glass also offer a high degree of resistance to breaking during storms and/or from intruders.

Glass pane types offer better visibility and longer life than plastic pane types, but glass is heavy and fragile. In general, plastics are most economical for people with small budgets or who live in apartments. However, while inexpensive and relatively easy to install, they are easy to damage.

Plastic panels, such as Plexiglas and acrylics are tougher and lighter than glass, but they may scratch easily. Some may turn yellow over time as well. Some plastic films may significantly reduce visibility and degrade over time when exposed to sunlight.

Frames

Wood, aluminum, and vinyl are the most common storm window frame materials. There are advantages and disadvantages to all types of frame materials. Although very strong, light, and almost maintenance free, aluminum frames conduct heat very rapidly. Because of this, aluminum makes a very poor insulating material.

Wood frames insulate well, but they weather with age. They also expand and contract in response to weather conditions. Wood-frame storm windows installed during the winter may not close easily during the summer, and those installed during the summer may fit loosely in the winter.

Wood frames can be quite heavy and thicker than metal frames. This can make storage difficult, reduce the view out the window, and reduce the amount of natural light in the room. Wood frames also require the most maintenance. There are, however, aluminum- or vinyl-clad wood frames that reduce maintenance requirements.

Vinyl frames are usually made of polyvinyl chloride (PVC) with ultraviolet light (UV) stabilizers to keep sunlight from breaking down the material. They may expand and warp at high temperatures, and crack in extremely low temperatures, however. Also, if sunlight hits the material for many hours a day, colors other than white will tend to fade over time

Installation

When installing storm windows, ensure they have weatherstripping at all movable joints; are made of strong, durable materials; and have interlocking or overlapping joints. See our do-it-yourself home energy savings project for step-by-step instructions for installing low-e storm windows.

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