Solar Heat Gain Control for Windows

Before innovations in glass, films, and coatings in the past decade, a typical residential replacement windows with one or two layers of glazing allowed roughly 75-85% of the solar energy to enter a building, which has a negative impact on summertime comfort and cooling bills, especially in hot climates.

In the summertime, the sun shining through your windows heats up the room. Windows with spectrally selective coatings on the glass reflect some of the sunlight, keeping your rooms cooler.

Install white window shades, drapes, or blinds to reflect heat away from the house.

Close curtains on south- and west-facing windows during the day.

Install awnings on south- and west-facing windows.

Apply sun-control or other reflective films on south-facing windows to reduce solar gain.

External window shading devices such as awnings, roof overhangs, shutters, and solar screens, and internal shading devices such as curtains and blinds, can control the entry of solar heat. However, shutters, solar screens, curtains, and blinds make rooms dark. Curtains and blinds also let in some of the undesirable heat. While exterior shading devices are about 50% more effective than internal devices at blocking solar heat, they may create problems with the building's aesthetics and are sometimes expensive to build. It is also impractical to construct roof overhangs to effectively shade east and west facing windows.

The following are the percentages of the radiant energy that different types of internal shading devices transmit, reflect, or absorb:

• Roller Shades: up to 25%, 15-80%, 20-65%
• Vertical Blinds: 0%, 23%, 77%
• Venetian Blinds: 5%, 40-60%, 35-55%