In cold climates, a large amount of heat is lost through windows during the winter. For instance, a double-pane window might allow as much as 10 times the amount of heat to leave a house compared to the same area of a typical 2 × 6 wall. It makes sense to upgrade or insulate windows in order to improve the thermal envelope of a home, especially in an area with a long heating season; however, windows are a very expensive component of the building envelope to replace. Replacing a single window can cost several hundred to more than a thousand dollars; therefore, people often resort to cheaper methods to reduce heat loss, such as shutters or curtains. Others may already have high-performance windows, but want to reduce heat loss even further by placing movable insulation over their windows during the cold winter nights.
To help guide these decisions, the Cold Climate Housing Research Center (CCHRC) in Fairbanks, Alaska, conducted a study of common window insulation methods and compared them in terms of thermal effectiveness, affordability, ease of installation, durability, functionality, and condensation resistance. The purpose of the study was to inform homeowners about the various advantages and disadvantages of different window treatments. As part of the research, CCHRC studied a variety of methods and windows in volunteers' homes to understand how the methods work in real-life situations. CCHRC also modeled the retrofit window treatments with Therm 6.3, a modeling program, to help explain more generally how they can help homeowners.