Twice as effective at insulation as the standard single pane version, double pane – AKA double glazed – windows consist of two sheets of glass which are separated by a metal or structural foam spacer. The glass panes enclose a layer of air or gas, generally krypton, xenon or the less expensive argon … or, conversely, a vacuum. This layer acts as insulation against the outside air, stabilizing the room temperature and reducing window condensatiom. It may also serve as a noise buffer. Recently, even more efficient triple glazed windows have become available.
Expensive but relatively long lasting, double or triple pane windows are guaranteed for 10 to 20 years. They are ranked according to their U-factor, a measure of heat transference similar to R-factor for a whole building; a low U-factor is the most desirable. Look for labeling from the National Fenestration Rating Council (NFRC).
Double pane windows should also have a thin coating of metal oxide to guard against solar heat gain and keep out harmful UV rays by means of reflection. This is called a low emissivity, or low E, coating.
Low Emissivity Film
As well, low E coatings may be added to the windows that you already have in your home, whether they are single or double pane, in the form of an adhesive film. As a retrofit, application of the film is quite a bit less costly than replacing windows. Its disadvantage is that although it is barely visible, low emissivity film does have a slight greenish tint and might block a certain amount of natural daylight.
Another relatively affordable retrofit, storm windows are a way of increasing energy efficiency that has been around for a long time. A second set of windows to be installed on either the inside or outside of the existing panes, they are made of glass, Plexiglas or acrylic.
Homeowners in frosty northern states have traditionally used their Minneapolis handyman skills to mount storm windows every fall and take them down in the spring. However, these days many energy experts recommend leaving your “storms” up year round, because in addition to insulating against cold winds in winter, they reduce the flow of hot air from outdoors to indoors in the summer months. Besides eliminating an unpopular task from your honey-do list, this means you won’t need a place to store your storm windows off season anymore.
Other Ways to Increase Window Energy Efficiency
Awnings or shutters, alone or in combination with one of the solutions above, will help shield your house or apartment against excessive sun and wind. Weather stripping or caulk around the window themselves will minimize drafts, as will draperies.
Frequent movers may want an insulating kit that allows them to apply plastic shrink wrap to windows. This is a low-budget solution that might only last for one winter. Be sure to opt for the low-density polyethylene type, rather than vinyl; the former is more eco-friendly as it doesn’t offgas during installation and may easily be recycled.
Buy insulated curtains or if you are handy with a sewing machine, do it yourself by adding foam padding, fleece or quilt batting. Or else use blackout material, which is not nearly as depressing as it sounds; this fabric comes in a wide variety of colors and designs and prevents heat gain in summer and heat loss in winter. Another DIY window insulation project is sewing a draft excluder, also a great way to repurpose fabric scraps.