What Makes a Window Energy-Efficient?

Energy-efficient windows keep your home comfortably warm or cool while saving you money for decades after they’re installed. Replacing your home’s windows with energy-efficient models not only improves comfort but also filters out damaging ultraviolet light. New ENERGY STAR® qualified windows can also save you hundreds of dollars a year in heating and cooling costs.

For the greatest energy savings, you want to choose replacement windows that are best suited to your climate.

Energy-Efficient Terms You Should Know

  • Heat gain and loss refers to direct transfer through the glass, heat radiation into your home, and air leakage through windows and skylights.
  • IGUs, or insulated glass units, are two or three window glass panes in one frame. Each pane is separated by a transparent, odorless, and inert gas, typically argon, krypton, or both, minimizing heat gain and loss.
  • Low-E refers to low-emissivity coatings, invisible layers that are applied to windows during the manufacturing process. They provide insulation and control heat transfer. While more expensive than windows without the coating, low-E windows can reduce energy loss by 30%-50%, making them a cost-effective investment.
  • SHGC, or solar heat gain coefficient ratings, measure the fraction of transmitted solar energy transmitted and let you know how well the window blocks the sun’s heat. The lower an SHGC rating, the less solar heat the window transmits.
  • U-factor rates a window’s performance by measuring its heat transfer rate and tells you how well the window insulates. The lower the U-factor, the better the window insulates. A window’s U-factor is affected by the window frame material, glazing, and low-E coatings.

How Windows are Insulated

Technology plays a big role in how energy-efficient windows work.

Glass coatings or glazing

Low-emissivity glass helps block 90% of the sun’s UV rays, keeping heat inside when it’s cold and outside when it’s hot. Glazing options include tints, gas fills, and reflective coatings, and all are designed to help save you money on your heating and cooling costs.

Spacer systems

Instead of metal, 100% polymer structural foam is now used to help keep windows thermally efficient and condensation-free. Spacers can lower the U-factor by .01%.

Window technology

Other advanced technologies that improve window energy efficiency include double and triple-paned windows and filling the space between insulated glass panes with Krypton gas to reduce heat transfer further.

Signs Your Windows Aren’t Energy-Efficient

Heat loss and gain through windows is one of the primary ways energy usage increases in homes. Signs your home’s windows aren’t energy-efficient enough include:

  • Inability to open or close windows easily or entirely
  • Reduced indoor comfort from drafts
  • Higher energy bills
  • Improper installation
  • High volume outdoor noise
  • Damage such as fog, broken glass, or rotted frames

Maintenance Tips For Maximum Energy Efficiency

Routine maintenance increases windows’ life span and keeps them as energy-efficient as possible. Together with periodic window inspections, here’s how to ensure your windows are operating at peak performance.

Keep them clean

Environmental factors can damage your windows and leave them less efficient. Though vinyl window frames aren’t necessarily affected by salt, the area around them can be. Washing it away is always a good idea.

Window caulk and weatherstripping

Heat and cold air can easily enter your home through gaps between the glass, frame, and window sash. Caulk or weatherstripping seal off drafts. Check them once a year to ensure they’re still providing adequate protection.

Window treatments and awnings

Insulated draperies and outdoor awnings can reduce the amount of solar heat gain by up to 65%. Awnings installed on western-facing windows can reduce heat gain by nearly 80%. Indoors, shades and drapes used together maximize sun protection and prevent heat loss.