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Using Window Energy Ratings to Evaluate Replacement Windows

posted on July 11, 2017 in Global Blogs

Using window energy ratings to evaluate energy efficient windowsBesides aesthetics and modernization, a key reason homeowners replace their windows is to achieve a more energy-efficient home. Choosing energy efficient windows is one of the most important considerations to realize a good return on investment for a window replacement. But there are a lot of factors, including proper installation, window material, and glass type that will eventually determine how much improved thermal performance and comfort you’ll see in your home.

This article will discuss different types of energy-efficient windows, what makes windows energy efficient, and some things to look for when shopping for energy efficient windows.

Why is energy efficiency important?

Old windows tend to allow air to escape through small cracks, missing or improperly installed sealing, or inefficient glass. When the air escapes, your home's heating or cooling system has to work harder to maintain the temperature that you want. That means you're paying higher electric bills, and having a negative effect on the environment.

  • Comfort - reduce air leakage from the outside to keep you more comfortable by eliminating drafts, reducing condensation, and reducing noise pollution. Do you ever find yourself avoiding sitting on the couch in the winter because it is right below the window? Energy efficient windows can help correct this problem by keeping the cold out and ensuring that all areas of your home are cozy.
  • Energy costs - keep your home warmer in the winter and cooler in the summer, putting less burden on your home’s heating and cooling systems and saving money. For typical homes, choose ENERGY STAR and save on average $101 - $538 a year when replacing single-pane windows.1
  • Environment - reduce your carbon footprint. When you replace single-pane windows you can save 1,147-3,839 pounds of CO2 a year, which is equivalent to 56-196 gallons of gasoline.2 New windows can conserve energy with quality construction and innovative glass options, improving sustainability and reducing your carbon footprint.

Window materials and energy efficiency

Energy-efficient windows are important, but how do they work? To keep your home warm in the winter and cool in the summer, windows need to reduce the amount of air that escapes through the frame and glass, control the rays of light entering and exiting your home, and the heat transfer through the window. The material of the window and the type of glass you choose will impact the window’s overall energy efficiency.

Frame material

Window frames can be constructed from a variety of materials. Different window frame materials provide different levels of thermal resistance (how much heat can transfer from the exterior of the window to the interior of your home), causing a varying influence on energy efficiency.

  • Wood frames are excellent insulators, conducting a low amount of heat or cold into your home.
  • Fiberglass composite material offers insulating properties similar to wood, conducting a low amount of heat or cold into your home.
  • Multichambered vinyl frames reduce heat loss for added energy efficiency compared to non multichambered vinyl frames
  • Aluminum is inexpensive and durable but has a poor insulation rating, meaning the frames conduct more heat or cold into your home than some other window material types.

Window glass

The type, thickness, and style of glass your window is built with all contribute to energy efficiency. Allowing certain solar rays to enter or exit your home, as well as reducing the conductivity of your glass, can impact the comfort of your home – and your heating and cooling costs.

  • Number of glass panes - Double-pane glass provides better insulation than single-pane, while triple-pane glass can further improve your energy efficiency.
  • Glass coating - Glass tinted with Low-E (low-emissivity) coating can reflect incoming solar heat. In the winter, Low-E glass reflects heat back into the room, keeping it warmer. In the summer, it reflects heat away from your home, keeping it cooler. There are different types of Low-E glass that have different benefits based on the climate.
  • Insulating gas - Many windows feature a safe, inert gas between the panes of glass. This gas has a higher resistance to heat flow than air, improving the thermal performance of windows.

Ways to increase energy efficiency

In addition to the frame and glass construction of a window, there are additional options that can impact your home’s energy efficiency.

  • Additional glass tinting - in addition to Low-E coating, many windows have the option of adding window tint. These can come in a variety of colors. Talk with a window expert to determine what the best option is for your home and region.
  • Optional foam - additional insulation within the frame may be available in some materials to further improve energy efficiency.
  • Professional Installation - even the best window can be inefficient if it is not installed properly. Proper installation is critical to maximize your energy efficiency.

How to choose energy efficient windows

Because some regions are hotter or colder than others, there are different types of energy-efficient windows that are designed for different climates. For colder climates, windows that let in more energy from the sun may be best. For warm climates, windows that keep out more energy from the sun may be best. Homeowners in temperate climates, with hot summers and cold winters, need windows that balance heating and cooling.

ENERGY STAR window ratings - Energy and climate zone map

For specific information on ENERGY STAR requirements, visit

Energy efficient replacement windows - Climate Zones

Energy Certifications - what do they mean?

The average consumer faced with a window decision cannot test and evaluate each window type independently before choosing, so they rely on certifications from third parties to help compare. When shopping for windows, pay special attention to these two certifications:


ENERGY STAR is an EPA program that certifies energy-efficient windows and doors, as well as home appliances. People across America look to the EPA’s ENERGY STAR program for guidance on how to save energy, save money, and protect the environment. The ENERGY STAR label is an independent certification to use less energy and reduce emissions that contribute to climate change.


When shopping for windows, look at the product’s NFRC label. NFRC stands for National Fenestration Rating Council® (NFRC). It’s a nonprofit organization that developed an energy rating program for windows. It’s a reliable way to determine a window’s “whole unit” energy performance - not just the performance of the glass itself. Reputable window manufacturers rate and certify their products with these requirements.

Window Energy Ratings - NFRC Label

Buying windows is a big decision, and there are many things to consider. Energy efficiency is just one of the factors that will contribute to your choice. Window products also have many unique features that increase energy efficiency, including different combinations of glass, material types, and other optional add-ons. But a window or door can only perform as well as it is installed. By following the manufacturer's recommended installation process, you can maximize your energy efficiency.

Still have questions about choosing energy efficient windows? Let us know in the comments below.

1 Source:

2 Source:

3For specific information on ENERGY STAR requirements, visit

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