Thermal shutters: save energy with moveable window insulation
Windows provide many benefits to a home, including light, air, passive heat, and aesthetics. Yet they are the weakest part of the building envelope. While today’s triple-pane windows are far more efficient than older single- or double-pane windows, they can be very expensive to replace. That’s why many people in cold climates resort to cheaper methods, such as shutters, curtains, or even moveable foam board, to lower their fuel costs. A CCHRC study analyzed nine types of “moveable window insulation” to see how much they actually improved the window’s efficiency and whether they created any unintentional problems, such as condensation on the window.
The most practical
The easiest thing you can do to improve old, leaky windows is to install plastic film or storm windows. These options not only improve your energy performance at an affordable price, but they also protect the window from condensation and frost. In our study, for example, plastic film upped the window’s insulation value by 25%. While it needs to be replaced every winter, you can buy a kit for around $20 and install it with nothing but scissors and a hair dryer.
Best energy improvers
For major energy gains, you need something a little thicker. The best energy improvers we studied were foam shutters, which can be as simple as cutting and fitting a piece of foam over your window or as elaborate as an automated sliding shutter that can be opened and closed each day. In our case study, adding exterior foam board made the windows four times more efficient (almost as efficient as a 2×4 insulated wall. The drawback is that you can’t see through the window. While it’s hard to give up daylight in the winter, it may be worth it in some areas like bedrooms or daylight basements.
While exterior foam is a good option, you should not add foam to the interior of the windows in a place like Fairbanks. That’s because it will make the window cold and greatly increase the likelihood of condensation, which can lead to mold, rot, and damage to the glass.
General tips
In general, it’s a good idea to stay away from interior window treatments. Anything that makes the window cold without blocking airflow allows the warm indoor air to deposit moisture on your glass and frame, which can easily turn to more serious problems like mold.
The exception to this rule are airtight insulation methods, such as plastic film. Interior storm windows also performed well in this study, almost doubling the insulation value of the window while also preventing warm, moist air from reaching the exterior window.
In summary, there are simple, cost-effective ways to reduce heat loss from windows as well as highly complex options that cost more and require more maintenance by homeowners. Each option has its pros and cons, and the best choice for you depends on your budget and personal preferences.