11 May 2020

Energy-Efficient Windows: How are Home Windows Rated?

Energy-Efficient Windows

Doors, windows, and skylights protect your home from the elements, just like wearing a coat protects you when you go out. Similar to picking out a winter coat, you should choose energy-efficient windows, doors, and skylights that are suitable for the climate in which you live. Some entries, windows, and skylights are better at keeping the house warm, and others are better at keeping a home cool.

Energy-Efficient Windows: How are Home Windows Rated?

Choosing energy-efficient windows is essential for both new and older homes. Heat loss and heat gain through windows are responsible for approximately 25 to 30 percent of residential cooling and heating energy consumption.

If you are choosing windows for a new home or replacing the windows in your existing home, it is vital to select the windows that are the most efficient and work best for your particular climate. It can be challenging to determine what windows are best for you. One of the best things that you can do is to learn how windows are rated for efficiency. Once you understand this, the process of choosing new windows for your home becomes a bit easier.

Energy Performance Testing

The NFRC (National Fenestration Rating Council) provides a program that certifies, tests, and labels windows based on energy performance ratings. An NFRC label is one of the first things that you should look for when determining the energy properties of a window. This label will help you compare products.

All Energy Star ® qualified windows will have an NFRC label. The Energy Star ® recommendation is based on solar heat gain and U-factors only.

Heat Loss and Heat Gain

Windows can lose heat in several ways, including:

  • Direct conduction through the glazing, glass, or frame
  • Radiation into the home from the sun and out of the house from objects including walls, furniture, and people
  • Air leakage around and through the window

Each of these properties can be measured and then rated through energy performance characteristics.


The u-factor is a rate a window conducts non-solar heat flow. The u-factor will often only refer to the glazing or glass of the window, depending on the system that is used. Some ratings will also include the spacer material and the frame of the window. A lower u-factor means higher efficiency.

Solar Heat Gain

The solar heat gain factor is the amount of solar radiation that comes through the window. This includes directly transmitted heat and absorbed heat. A lower solar heat gain means a more remarkable shading ability. Products that have high solar heat gain ratings are more effective at collecting heat in winter months. Windows with lower solar heat gain ratings will be more effective at keeping a home cool during the summer months.

Air Leakage

The rate of air movement near a window in the presence of a set amount of pressure determines the air leakage rating. Products with lower air leakage ratings have a tighter seal than ones that have a higher rating. It is important to note that the amount of air leakage is also dependent on proper installation.

Sunlight Transmittance

There are several ways that sunlight transmittance can be rated. The visible transmittance provides what fraction of sunlight is transmitted through the window. Products with higher VT ratings will allow more visible light. The VT rating that you choose will depend on how much light you need in a room.

Another rating that is used is the light to solar gain rating. This is the ratio between visible transmittance and SHGC. This number will provide a gauge of the efficiency of different types of glazing and glass types. The higher the number, the more light that is added without delivering too much heat.

Choosing the Right Windows

When it comes to choosing the right energy-efficient windows for your home, the rating should be one of the main factors that you consider. It is essential to look up information about the climate that you live in and learn more about the recommendations for your area. If you live in a cold area, you will want windows that produce and keep in heat for those cold winter months. For those in warmer climates, less heat retention is recommended. The ratings on windows will give you an excellent place to start your search.

America’s Best Choice Omaha, NE | Best Omaha Residential & Commercial Window Replacement Company

We pride ourselves on hiring only the most knowledgeable and experienced installers in the industry. We know how important this investment is to a homeowner and we want to educate you on every aspect you should consider before making your final decision.

America’s Best Choice Omaha also offers you a competitive price that you will afford without draining your funds. We also work with all insurance companies to ensure that we keep your costs to a minimum. Proudly, we are also an Accredited Business with the BBB!

We offer a  FREE, No-Obligation Estimates. Call us or fill out our form today if you have any questions on whether you need a minor repair or to replace your old roof with a new roof. We will be more than happy to offer our best recommendation that will offer more quality for your dollar.

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