Chapter

Windows

Windows can be one of your home’s most attractive features. Windows provide views, daylighting, ventilation, and solar heating in the winter. Unfortunately, they can also account for up to 25% of your heating bill. During the summer, your air conditioner must work harder to cool hot air from sunny windows.

Energy-efficient windows may have two or more panes of glass, warm-edge spacers between the window panes, improved framing materials, and low-e coatings, which are microscopically thin coatings that help keep heat inside during the winter and outside during the summer.

If your home has single-pane windows, as many U.S. homes do, consider replacing them with new double-pane windows with high-performance low-e (low-emissivity) or spectrally selective glass. In colder climates, choose windows that are gas-filled with low-e coatings on the glass to reduce heat loss. In warmer climates, choose windows with spectrally selective coatings to reduce heat gain.

If you’re building a new home, the higher cost of energy-efficient windows can actually be offset by allowing you to buy smaller, less expensive heating and cooling equipment. Install ENERGY STAR windows and use curtains and shade to give your air conditioner and energy bill a break. If you live in the Sun Belt, look into low-e windows, which can cut the cooling load by up to 15%.

If you decide not to replace your windows, the simpler, less costly measures listed here can improve their performance.

Cold-Climate Window Tips

Cold-climate windows keep heat in.

  • Double-pane windows with low-e coating on the glass reflect heat back into the room during the winter months.
  • During the cold winter months, you can use a heavy-duty, clear plastic sheet on a frame, or tape clear plastic film to the inside of your window frames. Remember, the plastic must be sealed tightly to the frame to help reduce air infiltration.
  • Install tight-fitting, insulating window shades on windows that feel drafty after weatherizing.
  • Close your curtains and shades at night.
  • Open your curtains during the day.
  • If you have windows located on the south side of your house, keep them clean so that they can let in the maximum amount of winter sun.
  • Install exterior or interior storm windows. Storm windows can reduce heat loss through the windows by 25% to 50%. Storm windows should have weatherstripping at all movable joints, be made of strong, durable materials, and have interlocking or overlapping joints. Low-e storm windows save even more energy.
  • Repair and weatherize your current storm windows, if necessary.

Warm-Climate Window Tips

Warm-climate windows keep heat out. In the summertime, the sun shining through your windows heats up the room. Windows with low-e coatings on the glass reflect some of the sunlight, keeping your rooms cooler.

Here are some things you can do to keep comfortable.

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

Long-Term Savings Tip

  • Installing high-performance windows will improve your home’s energy performance. While it may take years for new windows to pay off in dollar-for-dollar energy savings, the benefits of added comfort and improved aesthetics and functionality make the investment worth it much sooner. Many window technologies are available that should be considered.

Shopping Tips for Windows

  • Look for the ENERGY STAR label.
  • Check with your local utility company to see if any rebates or other financial incentives are available for window replacement.
  • High-performance windows have at least two panes of glass and a low-e coating, so make sure the windows you choose have these features, and not just a claim or label that says “high-performance.”
  • The U-factor for windows is similar to the R-rating for insulation. The U-factor measures the rate of heat transfer and tells you how well the window insulates. The lower the U-factor, the better the insulation. In colder climates, focus on finding windows with a low U-factor.
  • Low solar heat-gain coefficients (SHGCs) reduce heat gain. In warm climates, look for a low SHGC.
  • In temperate climates with both heating and cooling seasons, select windows with both low U-factors and low SHGCs to maximize energy savings.
  • Look for whole-unit U-factors and SHGCs, rather than center-of-glass (or 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. Be sure they’re installed according to the manufacturer’s instructions; otherwise, your warranty may be voided.