How Do Insulated Windows Work?

Control Conduction

All glass-paned windows gain and lose heat by conduction, convection and air seepage. The less conductive the window material, the greater the ability to impede these heat transfers from occurring. Energy-efficient windows use methods of coatings, multiple glass panes and gas fillers between the panes to control the heat transfers. Dual-pane windows are filled with inert argon or krypton gases that do not conduct heat well, and the separated two panes provide yet another physical barrier to conduction. The standard guide for measuring and discussing energy efficiency and controlling conduction, convection and air seepage is called the R-value. The higher the R-value, the greater the energy efficiency.

Manage the Sun

When it is cold outside, the sun’s heat and light is pleasing, and when warmed by the heat, we want to hold onto it. In warm climates, however, we often want to repel the heat and still have the benefit of the light. Energy-efficient windows are painted with clear metal oxide compounds that allow in the visible sunlight but repel up to 95% of heat energy. So in summer the house is cooler and in winter the heat is bounced back into the house to be absorbed by floors, walls and furnishings.

Low-E coatings can be placed on single-pane glass windows but are at their most efficient when used in conjunction with dual-paned, gas-filled windows. Tinting windows can also control the amount of heat and light transfer to varying degrees, depending on your climate. If you live in the desert, you can film your windows with a coating that repels heat but allows lots of light, which can reduce both cooling and lighting costs.

Choose Your Frame Wisely

All window framing materials are not created equal when it comes to insulating abilities. Energy efficiency can be lost in the framing of even a dual-paned low-E glass window. Aluminum frames provide the least energy efficiency, whereas aluminum cladding over wood or vinyl is slightly better, solid wood or vinyl is better still, and insulated vinyl or insulated fiberglass frames are the most energy-efficient frames on the market.