What makes a window energy efficient?

With electricity and natural gas costs projected to continue rising this year and the next, homeowners are turning to energy efficient windows to lower their utility bills and make their homes more comfortable.
What makes a window energy efficient?

Characteristics and features of energy efficient windows

With electricity and natural gas costs projected to continue rising this year and the next, homeowners are turning to energy efficient windows to lower their utility bills and make their homes more comfortable.

Energy efficiency is an important consideration when shopping for new or replacement windows. Energy efficient windows are designed to prevent cooled or heated air from escaping your home. They provide significantly better insulation than standard windows, thus maintaining indoor temperatures, reducing energy usage and lowering utility bills.

So, what exactly makes a window energy efficient?

Characteristics of Energy Efficient Windows

Air Infiltration

Most people refer to air infiltration as leaks and drafts. Air infiltration occurs through gaps, such as between window sashes or between the window frame and the wall. Poor manufacturing, improper installation and age can cause air infiltration.


Conduction is the transmission of heat or cold through a material. In windows, conduction occurs when there is a temperature difference on each side of the glass. Through conduction, hot air can get into a home during the summer, and cold air can get inside in the winter. Energy efficient windows made with multiple panes of glass and insulating gas help slow down conduction.


Low-emissivity refers to the condition of a surface that leads to low heat energy levels. All materials absorb, reflect and emit heat energy. Low-e coatings on glass reduce the amount of heat energy that can travel from one side of the window to the other.

How They Are Made

There are five features in the design and construction of a window that makes it energy efficient.

1. Quality Frame Materials

The material used to build a window frame is critical for maximizing the window’s energy efficiency. The most common materials used for energy efficient window frames are wood, vinyl, fiberglass, clad wood, aluminum, combination and composite (wood, plastic, metal) materials. High quality frame materials reduce heat transfer, providing better insulation and requiring less energy to cool or heat the home.

2. Double- or Multiple-Pane Glass

Double-pane (dual-pane) glass is much better for energy efficiency than single-pane glass. Two sheets of glass are sandwiched together with spacers, and the air pockets between the two layers are sealed shut and filled with gas. The gas-filled space between the panes acts an additional layer of insulation from the heat or cold outside. For even greater insulation, some energy efficient windows feature three or more panes.

3. Low-E Glass Coatings

Low-e coatings are special coatings that reflect infrared light, keeping heat outside during the summer and inside during the winter. An exterior low-e coating blocks ultraviolet and infrared light from entering the home while allowing visible sunlight to pass through the glass. Low-e coatings also block harmful ultraviolet light, which can damage interior furnishings.

4. Gas Fills

Some energy efficient windows are made with argon, krypton or other gases between the panes. When placed between the sheets of glass, these odorless, colorless, non-toxic gases insulate better than regular air.

5. Window Spacers

Window glass spacers, also known as space bars, are strips of plastic, metal or foam that separate, support and help seal in the gases that are injected between the panes. Spacers are bonded between glass panes with a variety of sealing materials to keep the glass sheets the correct distance apart and create an air-tight cavity. Non-metallic and metal hybrid spacers also insulate pane edges, reducing heat transfer through the window and improving energy efficiency.

How Do I Know a Window is Energy Efficient?

Look for the ENERGY STAR® and National Fenestration Rating Council (NFRC) labels on the window you want to buy or install. Window companies usually promote products that are Energy Star-certified and NFRC-labeled to inform their customers that they sell and install energy-efficient windows.

Air Master manufactures, sells and installs a variety of high-quality windows and doors. Calls Air Master for more information!