Building heat loss means increased energy costs. Much energy wasted occurs in the form of heat escaping through window glazing. Therefore the selection of an appropriate thermal-efficient window is crucial to reducing energy loss.
A window's main function is to allow in daylight (and eventually fresh air) and ensure a view of the outside for the occupants. However, windows also perform several other functions such as thermal comfort, protection against noise, security, etc. A window's thermal comfort (heat loss), is expressed by its U-value. A low U-value means a low loss of heat from the interior to the exterior of the building while a high U-value means the opposite. To increase the thermal performance of windows the following improvements can be applied:
Multiple (double) layers of glazing
Two panes of glass are better than one. The purpose of multiple (double) paned windows is to create an air space between the panes of glass that acts as an insulator. Double-pane windows are also better than single-pane windows because they reduce air convection (movement of air caused by differences in temperature).
Width of air space
Larger air spaces insulate better than smaller ones, but increasing the air space too much produces convection loops between the layers of glazing, and offers no further gain.
Low-conductivity gas fill
Filling the gap between the glass panes with low-conductivity gas such as argon or krypton at atmospheric pressure improves window performance and reduces heat loss.
Introduced during the energy crisis in the Seventies, low emissive coatings, applied on the insulating glass unit, enables the sun's short-wave energy to enter the room and at the same time prevents internal warm air from leaving the room. This means a warmer house and energy gains.
Low-conductivity, warm-edge spacers
To prevent thermal loss caused by spacers in insulating glass units, more and more consumers are demanding low-conductivity materials to separate panes of glass using so-called warm edge spacers.
Window frames are available in many styles, and can be made of different materials. Each of these materials (wood, PVC, etc.) offer different thermal performance.