Insulating with Storm Windows

Storm windows are used to increase a window’s insulation value by trapping air against the already existing pane of glass. The pocket of air acts as a layer of insulation, which, according to the U.S. Department of Energy (DOE), can reduce heat loss through windows by 25 to 50 percent. Storm windows can be placed on the interior or exterior side of the window and range from inexpensive plastic sheets or films designed to last one heating season to triple-track glass units with low-E coatings that should last as long as the windows. The following highlights the problems and benefits of each type:

Heat-Shrink Window Films

Heat-shrink window films are very affordable and effective insulators, making them cost effective in under a year. Using merely a hair dryer, scissors, tape, and a plastic film, these storm windows are also one of the easiest do-it-yourself options available to homeowners. Kits are available at most hardware and construction stores for less than 10 dollars, and each insulates five standard-size windows or at least one extra-large window.

Although this system provides an excellent seal and good visibility, note that it requires the use of two-sided tape, which can lift paint when removed. Additionally, this is a one-use material, so after the film is installed, the window cannot be accessed without removing or puncturing the film.

Spline and Channel

A step up from the heat-shrink film is a spline and channel system. This uses the same approach as a Ziploc bag seal to attach a plastic film in front of a window. The channel, as it is called, can be permanently fixed to the window frame with hardware or double-sided tape, and a clear plastic film zips into the channel and stretches across the window. The plastic is more durable than the heat-shrink film and can be reused for several years. The down side to this system is that the rigid plastic is opaque.

Magnetic Seal

Magnetic seal films are durable and strong and make the attachment system virtually indistinguishable from the main window. Their acrylic sheets are easy to attach and remove; however, thermal contraction and expansion and the weight of the acrylic sheet can sometimes cause the magnetic strip to detach unexpectedly. A few turn buttons or other supports can be attached to hold the unit firmly in place.

Glass

Glass storm windows are essentially regular windows that are added on to existing frames. They can either be permanently attached, made operable like sliding windows, or placed in a set of hinges. While this is the most expensive type of storm window, it will likely look the best, and if using windows with low-emissivity coatings, it will also likely insulate the best.

Other information

Note that the performance of windows also depends on how tightly they are sealed against the frame. If air is leaking around the windows, then their ability to reduce heat transfer, with storm windows or without, is largely negated. To learn more about how to detect and fix a “porous” home, see our weather proofing your home article.