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Concentration of CO2 in the Atmosphere

Energy-Efficient Windows Part 3

Tips: Windows

Windows can be one of your home’s most attractive features. Windows provide views, daylighting, ventilation, and heat from the sun in the winter. Unfortunately, they can also account for 10% to 25% of your heating bill by letting heat out.
During the summer, your air conditioner must work harder to cool hot air from sunny windows. Install ENERGY STAR®-qualified windows and use curtains and shade to give your air conditioner and energy bill a break.

Efficient windowIf your home has single-pane windows, consider replacing them with double-pane windows with high-performance glass—low-e or spectrally selective coatings. In colder climates, select gas-filled windows with low-e coatings to reduce heat loss. In warmer climates, select windows with spectrally selective coatings to reduce heat gain.

If you decide not to replace your windows, consider following these tips to improve their performance.

Warm Weather Window Tips

  • 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 heat gain.

Long-Term Savings Tip

Installing high-performance windows will improve your home’s energy performance. While it may take many years for new windows to pay off in energy savings, the benefits of added comfort, improved aesthetics, and functionality can offset the cost.

Shopping Tips for Windows

  • Look for the ENERGY STAR® label.
  • Check with local utilities to see what rebates or other incentives are available for window replacement.
  • Choose high-performance windows that have at least two panes of glass and a low-e coating.
  • Choose a low U-factor for better insulation in colder climates; the U-factor is the rate at which a window, door, or skylight conducts non-solar heat flow.
  • Look for a low solar heat gain coefficient (SHGC)—this is a measure of solar radiation admitted through a window, door, or skylight. Low SHGCs reduce heat gain in warm climates.
  • Select windows with both low U-factors and low SHGCs to maximize energy savings in temperate climates with both cold and hot seasons.
  • Look for whole-unit U-factors and SHGCs, rather than center-of-glass (COG) U-factors and SHGCs. Whole-unit numbers more accurately reflect the energy performance of the entire product.
  • Have your windows installed by trained professionals according to manufacturer’s instructions; otherwise, your warranty may be void.

Consider windows with impact-resistant glass if you live along a coast or in areas with flying debris from storms.

Learn More at http://energy.gov

Cold Weather Window Tips

  • Use a heavy-duty, clear plastic sheet on a frame or tape clear plastic film to the inside of your window frames to reduce drafts.
  • Install tight-fitting, insulating window shades on windows that feel drafty after weatherizing.
  • Close your curtains and shades at night to protect against cold drafts; open them during the day to let in warming sunlight.
  • Install exterior or interior storm windows, which can reduce heat loss through the windows by 25% to 50%. They should have weatherstripping at all movable joints; be made of strong, durable materials; and have interlocking or overlapping joints.
  • Repair and weatherize your current storm windows, if necessary.

Heat-Absorbing Tints

Heat-absorbing window glazing contains special tints that change the color of the glass. Tinted glass absorbs a large fraction of the incoming solar radiation through a window, reducing the solar heat gain coefficient (SHGC), visible transmittance (VT), and glare.

Some heat, however, continues to pass through tinted windows by conduction and re-radiation, so the tint doesn’t lower a window’s U-factor. Inner layers of clear glass or spectrally selective coatings can be applied on insulated glazing to help reduce these types of heat transfer.

The most common gray- and bronze-tinted windows are not spectrally selective, and reduce the penetration of both light and heat. Blue- and green-tinted windows offer greater penetration of visible light and slightly reduced heat transfer compared with other colors of tinted glass. In hot climates, black-tinted glass should be avoided because it absorbs more light than heat. Tinted, heat-absorbing glass reflects only a small percentage of light, so it does not have the mirror-like appearance of reflective glass. Note that when windows transmit less than 70% of visible light, indoor plants can die or grow more slowly.

Reflective Coatings

Reflective coatings on window glazing or glass reduce the transmission of solar radiation, blocking more light than heat. Therefore, they greatly reduce a window’s VT and glare, but they also reduce a window’s SHGC. Reflective coatings usually consist of thin, metallic layers, and come in a variety of colors, including silver, gold, and bronze. Reflective window glazing is commonly used in hot climates to control solar heat gain. The reduced cooling energy demands can be offset by the need for additional electrical lighting, so reflective glass is used mostly for special applications.

Source: http://energy.gov

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