Because of the numerous openings between the slats, it’s difficult to control heat loss through interior window blinds, but the slats offer flexibility in the summer. Unlike shades, you can adjust the slats to control light and ventilation. For example, when completely closed and lowered on a sunny window, highly reflective blinds can reduce heat gain by around 45 percent. They can also be adjusted to block and reflect direct sunlight onto a light-colored ceiling. A light-colored ceiling will diffuse the light without much heat or glare.
When properly installed, window shades can be one of the simplest and most effective window treatments for saving energy.
Shades should be mounted as close to the glass as possible with the sides of the shade held close to the wall to establish a sealed air space. You should lower shades on sunlit windows in the summer. Shades on the south side of a house should be raised in the winter during the day, then lowered during the night.
For greater efficiency, use dual shades—highly reflective (white) on one side and heat absorbing (dark) on the other side—that can be reversed with the seasons. The reflective surface should always face the warmest side—outward during the cooling season and inward during the heating season, and they need to be drawn all day to be effective.
Quilted roller shades and some types of Roman shades feature several layers of fiber batting and sealed edges. These shades act as both insulation and air barrier, and control air infiltration more effectively than other soft window treatments.
Pleated or Cellular Shades
Several manufacturers have designed two- or three-cell pleated or cellular shades with dead air spaces, which increase their insulating value. These shades, however, provide only slight control of air infiltration.
Window shutters—both interior and exterior—can help reduce heat gain and loss in your home.
Interior shutters need a clear space to the side of the window when they’re opened. They also require hardware that is fastened to the window jams or trim. Properly designed exterior shutters may provide the best possible window insulation system. They offer several advantages:
•No use of interior space
•No thermal shock to windows if left closed.
Like window blinds, louvered shutters work best for summer shading. Movable or fixed louvers allow ventilation and natural daylight to enter a room while blocking some direct radiation. However, they won’t provide much insulation against heat loss in the winter.
Source: U.S. Department of Energy