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Upgrading or improving your windows is an important component of your home’s energy efficiency. According to the U.S. Department of Energy, heat gain and loss through windows consume 25% to 30% of residential heating and cooling energy use.

Understanding efficiency factors

If you’re evaluating your windows’ energy efficiency, start by identifying what kind you have. Are they single pane or double pane? Looking closely at the window’s edge, you can see the number of windowpanes. Are the frames metal, wood or vinyl? Some manufacturers etch the make and model numbers in the corner of the glass so that you can look up the manufacturer for more information.

Window efficiency

Several components can make windows more efficient. High-quality frame materials insulate and reduce heat transfer. Two or more panes of glass with space in between (filled with air or gas) improve the window’s insulation capability. Warm edge spacers hold the panes of glass the proper distance apart and help insulate the edges of the panes. Low-emissivity coatings applied to the glass can reflect infrared light, keeping the heat in during the winter and out during the summer.

Window efficiency is rated in U-factor and Solar Heat Gain Coefficient (SHGC). U-factor measures heat transfer through the window, which relates to how well it insulates. The lower the U-factor, the more efficient the window. The SHGC measures how effectively the window blocks heat from the sun.

Considerations for replacing windows

If you want to replace your existing windows, shopping for ENERGY STAR®-certified windows is recommended. ENERGY STAR sets specific U-factor and SHGC requirements based on geography so you get the best fit for your location. Replacement windows offer additional benefits, like improved operability and aesthetics.

Storm windows are a lower-cost solution for some homes. Traditional storm windows are made with clear glass. Low-emissivity storm windows have energy savings similar to replacement windows at about a third of the cost. Storm windows are mounted to the interior or exterior and are available in operable styles, so you can still open and close your windows. Look for ENERGY STAR-certified models.

If you want to maintain the historic architecture of your existing windows, low-emissivity storm windows are a great option. Some companies can refit your existing window frames with custom double-pane glass and weatherstripping. 

Maintenance options

If new windows or storm windows are outside the budget, your best bet is to maintain your existing windows. Keep the paint and caulking on the exterior in good condition. That will help prevent damage from the elements. Caulk around the inside trim, ensure sash locks are correctly installed and seal tightly when locked. There are a variety of weatherstripping options for windows to keep drafts at bay.

As with any home improvement project, be sure to get multiple quotes to compare pricing and scope of work. You may find additional savings with rebates from your electric cooperative or state or federal tax credits for window upgrades.

Whether you replace or make improvements to what you have, adding efficiency to your windows will add year-round comfort to your home.

Miranda Boutelle writes on energy efficiency topics for the National Rural Electric Cooperative Association, the national trade association representing more than 900 electric co-ops.

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