How To Choose The Best Windows Based On Efficiency Ratings

With all the options available with windows, it can be hard to know which type to purchase. A lot of homeowners consider purchasing new windows as a way to cut back on energy used and lost in a home, and this might be one of the main reasons you are considering replacing your windows. If so, you will need to compare your options by learning, understanding, and evaluating the various types of window efficiency ratings. Here are four of the main ratings you will need to look at as you make this decision:


The first type of efficiency rating is for the u-factor of a window. U-factor refers to how well a window keeps heat inside a building. As you look at various types of windows, you may see ratings from 0.20 to 1.20. These ratings are offered by the National Fenestration Rating Council (NFRC), and lower numbers are better.

Windows can lose heat through the glass, frame, and material used to hold them in place, and the U-factor bases the rating on all of these factors. A window that is rated at 0.20 is the best window for holding in heat, and this would be considered the most efficient window in terms of U-factor.

Solar Heat Gain Coefficient

The second way efficiency is rated with windows is with the solar heat gain coefficient (SHGC) rating. SHGC represents how well a window keeps heat outside of a building. This refers to summer months when the weather is hot and the sun is shining in.

When windows are rated for SHGC, the result is a number that is between 0 and 1. Lower numbers represent more efficiency for blocking out heat, and the rating you should look for will depend on where you live.

If you live in an area that has a cold climate, this rating will not really matter much for your home. On the other hand, if you live in Florida, or any area with a hot climate, you should look for a SHGC rating that is as close to 0 as possible. Windows with low SHGC ratings will help homes in warm areas stay cooler.

You can add window film to your windows to reduce the heat that comes through, but it is easier to purchase windows that automatically do this.

Sunlight Transmittance

The third efficiency rating to examine is the sunlight transmittance. This rating is used to explain how much light is allowed through a window. Sunlight transmittance is often labeled as visible transmittance (VT), and the rating is labeled from 0 to 1.

Windows with a VT rating of 0 allow more light to come through than windows with a rating of 1. You may want to allow more sunlight to come through, or you may prefer protecting your house by blocking some of the light rays from the sun.

Air Leakage

The final rating to consider and compare is the air leakage rate. This rate tells you how much air a window allows to pass through, and finding a window that has a 0.30 rating or less is best.

As you're comparing window options, read the labels. You will find ratings from two main organizations, which are the NFRC and the U.S. Department of Energy. Windows are not labeled until they have been thoroughly tested and evaluated, and you can trust the ratings from these two organizations.

By purchasing highly-efficient windows, the temperature in your home might stay more consistent and comfortable, and you might experience savings on your energy bills. To learn more about ratings and options with windows, look at sites like or contact a window contractor in your area.