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Pay Attention to Doors, Windows and Skylights for Greater Energy Savings

In many homes, doors, windows and skylights pose a real potential for substantial air and energy loss that can make your indoor spaces uncomfortable and drive up your monthly energy bills. Taking steps ranging from winterizing doors, windows and skylights to replacing these features altogether can dramatically improve your home comfort, increase HVAC system performance and efficiency, and reduce the amount you spend each month to keep your home warm or cool, as appropriate to the season.

Doors, Windows and Skylights: The Basics

It's hard to imagine a home without doors and windows. Doors provide simple in-and-out access, while windows provide illumination and ventilation. Skylights are less common in residential settings, but they, too, are a source of indoor lighting and can be an element of architectural design. All of these features require an opening in the wall or ceiling of your home. This creates spots where conditioned air can leak out around frames or outdoor air can seep inside. Doors that are often opened and closed can account for substantial air and energy losses.

Heat gain and loss can also occur directly through the frame or the glass mounted in doors, windows and skylights. In the summer, this heat gain can significantly raise the temperatures inside your home, increasing demands on your air conditioning equipment. Heat can also radiate through doors, windows and skylights and into your home from sunlight, and out of your home through walls, furniture, and even people.

When conditioned air and energy are lost at doors, windows and skylights, that air is wasted before it can heat or cool your home. Your HVAC system must work harder to make up for those leaks and keep your indoor spaces at the temperatures you prefer. By tending to doors, windows and skylights, you can stop much of this energy loss, and keep your heating and cooling bills at a much more reasonable level.

Doors, Windows and Skylights: Energy Performance Ratings

By looking for the performance ratings of doors, windows and skylights, you can determine how much heat gain or loss is likely to occur. Check for ratings such as:

  • U-factor: This is the rate at which doors, windows and skylights conduct non-solar heat flow. Sometimes the U-factor may indicate just the energy conduction properties of the glass by itself, while other U-factor ratings may refer to glass, frame and construction material. Low U-factor ratings indicate high-efficiency windows.
  • Solar heat gain coefficient (SHGC): This rating describes the amount of solar heat and radiation that flows through doors, windows and skylights. The heat can be transmitted directly from sunshine or absorbed through the frame and surrounding material. Lower SHGC ratings indicate less solar heat transmission. High-SHGC items are a better choice for colder climates since they are more effective at collecting solar heat. Low-SHGC products are better in warmer climates since they block solar heat gain and reduce home cooling loads.
  • Air leakage: This rating refers to the rate of air movement and loss around the frame or casing of doors, windows and skylights. Lower air leakage ratings indicate higher-efficiency windows and less loss of air and energy.

Doors, Windows and Skylights: Preventing Energy Loss


Exterior doors present a significant potential for air leakage and energy loss. Consider these options to make the doors in your home more energy efficient and less likely to leak.

  • Install weatherstripping to seal spaces between the door and the frame: Foam or rubber weatherstripping can block gaps and openings between the door itself and the frame. This can stop air loss and leakage in both winter and summer. Weatherstripping is appropriate for all types of doors, including sliding glass doors.
  • Caulk around door frames and casings: Seal gaps, holes or openings around the door frame and casing with an appropriate type of caulk. Caulk is specially designed to easily flow into openings and produce a weatherproof and airtight seal. Latex caulking is the most common type used for sealing door frames and casings.
  • Caulk around any glass panes in the door: Ensure the areas around glass panes in the door are sealed with silicone caulking. This type of clear, rubbery caulk is best suited for sealing around glass panes and glazing.
  • Replace doors with higher-efficiency types: If replacing exterior doors, look for high-efficiency models that are delivered pre-hung and well sealed. Pre-hung doors already have the door installed within their frame or casing. High-efficiency doors will have a high R-value, which shows how well the door will resist the flow of heat. Look for doors with a steel or fiberglass outer layer over an inner layer of polyurethane insulation.


Windows provide multiple opportunities to reduce energy loss and improve efficiency.

  • Seal and caulk around glass panes, frames and casings: As with doors, sealing and caulking gaps and openings around the window glass, the frame and the casing will improve the seal and stop air and energy loss.
  • Apply window treatments and films: Window treatments are designed to block or reflect sunlight and prevent heat gain by keeping sunlight out of your home. Reflective films and treatments reflect heat and sunlight away from the window, while blocking treatments stop sunlight from getting through the window glass or glazing.
  • Use low-emissivity glass or coatings: If replacing window glass, use a low-emission type of glass or surface coating that helps prevent sunshine from getting through. This type of glass significantly lowers the U-rating of the window.
  • Use window shades: Install roll-type window shades that can be lowered or raised as needed to block sunlight or let more light in. Choose two-tone shades with a reflective white surface that faces the window and a darker surface facing inward.
  • Close or open drapes and curtains: Use the drapes and curtains to either block sunlight or let more light inside. Closing drapes can prevent significant amounts of heat gain caused by sunlight streaming through the windows.
  • Install awnings: Outdoor awnings can shade windows and block substantial amounts of sunlight. An awning over windows can cut heat gain by 65 to 75 percent or more.

If you are installing new windows or replacing old ones, pay particular attention to the type of material the window frames and casings are made of.

  • Aluminum or metal frames: These types of window frames are very common and functional, but they tend to conduct heat easily and quickly. If you are using a metal window frame, make sure it has a thermal break, which is a plastic strip between the frame and sash and improves the insulating characteristics of the window.
  • Wood frames: Wood is another common type of window frame material, but keep in mind that wood will expand and contract as temperatures change, which could lead to breaking of seals or creation of gaps where air loss can occur. Wood frames likely will require additional attention and maintenance to keep them well sealed.
  • Composite frames: Composite wood frames, such as those made of particleboard or laminated strips, are good choices for providing limited heat conduction. They have similar characteristics as solid wood frames.
  • Fiberglass frames: Fiberglass frames are solid and practical choices for windows. They usually have internal air cavities that can be packed with insulation, improving the window's efficiency over a similar wood or vinyl frame.
  • Vinyl frames: Vinyl is a lightweight but sturdy material used in window frames. They can also be filled with insulation to improve performance and efficiency. They resist moisture better than wood or composite frames and require no painting and little maintenance.


Skylights are usually intended to offer additional indoor lighting or ventilation. When choosing a skylight:

  • Check efficiency and energy performance ratings: Skylights with energy performance ratings appropriate for your climate will be more energy efficient and will improve indoor comfort. Energy Star-certified skylights will be even more reliable.
  • Choose appropriate glazing: The glazing in a skylight is usually plastic or glass, so make sure the type you choose is appropriate for the application.
  • Ensure convenient operation: Make sure the skylight you choose can be operated easily, opened and closed with as little trouble as possible.
  • Be aware of physical size and positioning: The physical dimensions of the skylight will affect how much sunlight gets through and into your home. In general, keep skylights to no more than 5 percent of the total floor area in rooms with multiple windows, or 15 percent in rooms with few windows. Remember that the directional orientation of the skylight also can affect the amount of lighting and heat gain provided by the skylight.
  • Ensure proper installation: Consult with your local trusted HVAC or construction professional for proper installation of a skylight. Your building pro will make sure the skylight is installed at the correct angle and tilt to perform at its best.

Comfort24-7 is one of the leading HVAC services companies in the Chicago area, including northwest Indiana and southwest Michigan. Contact us today for more information on how energy-efficiency changes in doors, windows and skylights can make a significant difference in both indoor comfort and home heating and cooling costs.

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