Everything You Need to Know about Window U-Factor

Energy efficiency is the primary concern of many homeowners in determining the windows to install in their homes. Although many features contribute to a window’s energy efficiency, the window u-factor is the most significant.

window u-factor ratings

To have a better insight of the windows that will be installed in your home, you must understand the terms involved with them. A window’s u-factor is vital to know because it tells you whether your windows will hold out well in extreme weather. Here is everything you need to know about window u-factor.

What is U-Factor?

Window manufacturers rate windows using several factors, including u-factor, that is crucial to their overall energy efficiency. Window u-factor determines the insulation properties of a window.

Also known as the u-value, the u-factor system was coined by the National Fenestration Rating Council (NRFC). NFRC is a nonprofit organization that deals with rating the energy efficiency of building materials and highly acknowledged in the window industry. They’re so renowned that the US Department of Energy considers the u-factor when determining whether a window is regarded as Energy Star Certified or not.

The u-factor controls the rate of heat transfer and shows you how much heat is gained or lost through your windows. According to Energy Star, these ratings range from 0.25 to 1.25. A window with a lower u-factor is more energy-efficient than ones with a higher u-factor value. A lower u-value shows that the window keeps more heat inside the house.

This is highly desirable in colder climates like the Northeast. Conversely, a higher u-value means the window allows more heat to escape. This is convenient in very sunny and hot locations where you need to avoid the greenhouse effect in your home.

Midwest homeowners need to be on the lookout for u-values when installing new windows, replacing new ones, or moving into a new home. Since the winters get extremely cold, you need every bit of heat to remain inside your home.

If your home is perpetually losing heat in the winter, you will depend heavily on your furnace to keep it at the right temperature, and your heating bills will overwhelm you in this case.

How U-Factor is Calculated

The actual formula to calculate the u-value is simple. As a homeowner, most likely you will not encounter a situation that requires you to do the math because the values are usually labeled on the windows. However, it’s always good to know what it involves so that you have sufficient knowledge when deciding which windows to install.

R-value is a unit that measures a material’s resistance to heat, also known as thermal resistance. The u-factor is the opposite since it measures the window’s ability to keep heat from escaping. Now, the u-factor of a product is the inverse of its r-value.  That is, U-factor=1/R-value.

The best performing triple or double pane windows will often have u-values of 0.30 and below. A lower value shows a more energy-efficient product.

Why the U-Factor is Important

window installer replacing windows

Now that you know how to determine the window u-factor, you may wonder why it matters for your windows. Since the u-factor indicates how effectively your windows retain the heat inside your home, it is one of the most crucial factors in a window.

U-value helps you save lots of money during winter when you need to keep your furnace on. Windows with a poor u-value will not retain much heat indoors and it will force you to keep your furnace running. If you live in states like Wisconsin or Illinois where it gets extremely cold, your windows must have a low u-factor.

Not all manufacturers opt to test and certify their products and materials with all the organizations, and usually, they choose one certification over the other. So, make sure you find the Energy Star and NRFC label on all the windows your purchase. NRFC issues unbiased figures for you to consider when making your decisions, and Energy Star shows whether these figures meet their superior performance standards. Thus, being on the lookout for these certification labels and performance ratings will help you make the right choices for your home window installations.

Now that you know about window ratings, labels, and certifications, you are assured of a more comfortable and energy-efficient home. Before you get your windows installed or replaced, or move into a new home, ensure you know the window u-factor ratings so that you will remain comfortable in your home even during extreme weather conditions outside.

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