Window Terminology It Pays to Understand

30 November 2016
 Categories: , Blog

Investing in new windows is a great way to improve the appearance of a home while also improving heating and insulation efficiency. Yet many people find themselves utterly confused by the wealth of jargon used to differentiate different models. If you would like help in making sense of what all that technical language is referring to, read on. This article will discuss two phrases you should absolutely be acquainted with when purchasing energy efficient windows.


If you have ever purchased insulation, you have likely already encountered the phrase R-value. This term is used to express the ability of a particular insulation to retain heat. U-value is a similar term, yet one that is used exclusively when discussing windows. To put it in more technical terms, the U-value expresses the amount of heat (in BTUs) that are able to penetrate a single square foot of window glass in the course of a single hour.

R-value and U-value differ in a way that often leads to large amounts of confusion for consumers. You see, generally speaking, the higher the R-value, the better the insulation is at preventing unwanted heat loss. Yet the opposite holds true where U-value is concerned. Windows with the greatest ability to prevent thermal transfer have a low U-value. Always be sure to check the NFRC label of a window to learn its U-value; this information is very helpful when comparing different models.


SHGC stands for solar heat gain coefficient. This term is related to U-value, though it comes at the issue of insulation from a somewhat different angle. U-value designates a window's ability to resist energy loss. SHGC, on the other hand, designates a window's ability to prevent solar heat from entering your home. The lower the SHGC, the better a job the window will do at keeping the sun's rays from causing unwanted heat gain in your home.

Investing in windows with a low SHGC is especially important for those who live in hot climates. Generally speaking, the more time you spend running your air conditioner each year, the more important it is to have windows that help to keep outside heat where it belongs--outside. Yet it's important to realize that a low SHGC isn't always a desirable thing. Those who live in colder climates often have just as much to gain from solar heat, especially during the winter months.

Determining the ideal SHGC for you requires determining whether you have more to gain from allowing the sun's heat in during the winter or keeping it out during the summer.