A Guide to Door and Window Energy Performance


American homeowners are reducing home energy bills by up to 25% by installing certified, high-energy-performance doors and windows. As they do this, they are improving the curb appeal and market value of their homes. Keep reading to learn everything you need to know about door and window energy performance.

What Is Energy Performance?

The extent to which a door or window keeps your home warm or cool is its energy performance. But where do the energy ratings come from? The National Fenestration Rating Council (NFRC) is the body entrusted by the U.S. Environmental Protection Agency and the U.S. Department of Energy to provide energy performance ratings for windows and doors for its ENERGY STAR® program. 

The organizations provide energy efficiency ratings by judging the u-factor, solar heat gain coefficient, and the air leakage rate of a door or window. Look for the ENERGY STAR® label when shopping for the most energy-efficient doors and windows. 

Energy Efficiency Terms

NFRC ratings represent the entire window performance including the frame and glass.

  • U-Factor is an indication of how much non-solar heat the product is transferring. You will want a low number, usually between .25 and 1.25, with a lower number transmitting less energy.
  • Solar Heat Gain Coefficient, between 0.0 and 1.0, indicates the fraction of solar heat and radiation the product will transfer.
  • Air Leakage measures how much air a door, window, or skylight will allow to pass. The lower the better.
  • Visible Transmittance measures the amount of light in the visible spectrum the glass will transfer. The higher the VT number, the more light the glass will permit. You can still let the light in while limiting the harmful UV rays that can cause fading.
  • Condensation Resistance rating is a relative assessment of the window’s condensation resistance on a scale of 0-100. You’ll want a high number in this case.

Why Is Window and Energy Performance Important?

These are three reasons why homeowners are keen on improving the energy efficiency of their doors and windows. 

First, it saves money. 55% of Americans’ utility bills go towards heating and cooling their homes. Energy-efficient homes that keep warm in winter and cool in summer save their owners a lot of money in energy costs. Homes built according to ENERGY STAR® standards use approximately 15% less energy than those built to the 2009 International Energy Conservation Code (IECC). 

Reducing our energy consumption helps create a cleaner and more sustainable environment for the population. Additionally, installing windows and doors with the best energy performance ratings increases the comfort of your home.

Factors That Make Doors and Windows More Energy Efficient

The NFRC looks at different factors when evaluating the energy efficiency of windows and doors. So, what is a good energy performance rating? This depends on the climate where the homeowner lives. Help your clients find the ideal window ratings for their home. Below are the general features of an energy-efficient window or door.

Qualities of ENERGY STAR® Certified Products

Here are some qualities of the ENERGY STAR® certified products:

Quality Frame Materials

Durable, low-maintenance window frames have better insulation and prevent heat transfer and air leakages. The best frame materials include fiberglass, wood, vinyl, and aluminum. Some window frames can also have a combination of materials or composite materials. Composite frames are made of several materials blended during the manufacturing process to create durable low-maintenance frames. Combination frames have different materials in different parts of the frame.

Multiple Window Panes

Energy-efficient windows must have two or more panes of glass with an insulating gas or air-filled space between the panes. This setup provides both energy and sound insulation as well as impact resistance.

Gas Fills in Between Panes

Energy-efficient windows contain at least two and up to four panes of glass with gases like argon and krypton between those panes. These gases provide better insulation than air alone. Both Argon and Krypton are odorless, colorless, and non-toxic.

Glass Spacers

The panes of glass have spacers that separate and help support the glass. The glass is adhered to the spacers creating a sealed, insulated glass unit (IGU). To reduce heat transfer through the window, the spacers are made of non-metallic or hybrid metal/non-metal materials.

Low Emissivity (Low-E)

Special coatings on the window reflect infrared light and ultraviolet light. This keeps the home warm in winter and cool in summer while protecting interior furnishings from fading.


Doors and windows must have a tight fit and seal to reduce air leakage around the edges. Modern doors are engineered with specially shaped and positioned weatherstripping that form a tight seal around all four sides of the door.

Energy-Efficient Door Materials

Quality doors are made of a strong core material like fiberglass or steel then are filled with closed-cell expandable polyurethane foam. This is part of an energy efficient and quiet door system. Wood is still an excellent insulator, and when the exterior is clad in extruded aluminum, it makes for an extremely durable, energy efficient, and long-lasting product.

Provide Expert Advice and Quality Products

High-performance doors and windows save you money while improving the comfort of a client’s home. It also reduces the negative environmental impact of unclean energy. 

Whether a homeowner wants to add some extra sealing and insulation or start a replacement project, the reduction in energy bills will cover the cost of improvements and improve home value.

Contact us today to learn more about our products and how we can help with your upcoming projects.

window and door energy performance infographic