Window Replacement Ratings | Energy Star, NFRC, U Factor, R-Value
When comparing the same type and style of window from different manufactures or even different lines from the same manufacturer, you have probably noticed one thing: no two windows are exactly the same. Don't panic! There's no need to resort to anything as drastic as defenestration - or jumping out of a window. In order to ensure that your replacement windows will provide you with great home comfort and energy cost savings, the National Fenestration Rating Council or NFRC and Energy Star provide a useful rating system for evaluating window quality and energy efficiency.
It can be difficult to compare claims made by different window manufacturers, mainly because they often use different window measures and rating terms to sell their products. For instance, some may use center-of-glass R-value and shading coefficient, while others use whole-window U-factor and solar heat gain coefficient. Fortunately there is now one place to look that has standardized ratings for windows - NFRC. The National Fenestration Rating Council (NFRC) is a nonprofit coalition of manufacturers and window experts that has set standards for testing and labeling windows.
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The NFRC Window Replacement Rating System
The NFRC has developed a fairly comprehensive window performance / energy rating system where they provide uniform and definitive benchmarks by which all window companies must now measure a window's energy performance. You can easily compare windows from different manufactures or different lines from the same producer because the information is handily and precisely presented in an easy to understand summary. However, you should be forewarned that windows are evaluated and rated when they are new and therefore long-term resilience is not taken into account. In addition, the Council does not perform studies on already installed windows or their history.
National Fenestration Rating Council
The key element to the National Fenestration Rating Council rating system is a window's U-factor. The NFRC gives each window a U-factor rating. The first number after the words "U-factor"? is the rating that's appropriate for residential purposes. It will be marked AA? or Residential.? The U-factor marked "BB"? or "Non-Residential"? is for commercial window applications. The U-factor on the NFRC label always refers to the whole window. To make sure you are comparing apples to apples, ask for the NFRC ratings even when there is no label on your window replacement. Also, be sure to use the same size windows for comparison, because the ratio of glass to framing affects the result.
U-value measures how much heat actually flows through a material. NFRC has U-value measurements of different replacement window systems. Simply put, the lower the U-value, the greater a window's resistance to heat flow and the better its insulating value. U-factor rating ranges from 0.10 to 1.20. The lower the U-value, the lower your heating costs. You may also want to compare air leakage. This rating corresponds to the ratio between the number of cubic feet of air that passes through a window divided by the square feet of window area. The lower the AL is, the smaller the leakage.
Another factor to consider is Solar Heat Gain Coefficient (SHGC), which measures how well a product blocks heat caused by sunlight. SHGC is the actual measurement of solar radiation (infra red energy or solar heat) that passes through home replacement windows. SHGC is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits. Whether you want a high or low SHGC number depends on where you live. In the north, where your primary concern is probably heating your home, a high number may work to your advantage. On the other hand, in the south, where the goal much of the time is keeping the heat out, a lower SHGC would be desirable.
Next is Visible Transmittance or VT. VT measures how much light gets thru the window glass. This is also a rating between 0 and 1 and like CR the higher the number, the more light gets through. The typical piece of clear annealed glass has a VT of .93, which means 93% of the light that hits the glass passes through. Add a second lite and VT goes down by an additional five percent. The higher the VT, the more light that gets through the window. The lower the UV transmittance — the less fading of your drapes and carpet.
One final factor is condensation resistance or CR. CR measures the ability of windows to resist the formation of condensation on the interior surface of the product. Here, higher numbers are better than the lower numbers.
Many of the stickers won't include ratings for all these categories since they are not mandatory. For the most part, the two most important numbers to look at are U-Value and Air Infiltration. U-Value indicates how good an insulator the window is, and air infiltration indicates how drafty the window is.
Energy Star Program
In 1992 the United States Environment Protection Agency (EPA) established the Energy Star program. The Energy Star Window Program and leading window manufacturers have worked together to provide consumers with windows that are energy efficient. This program has paved the way for valuable strides in window technology. Every ENERGY STAR-qualified window is independently certified to perform at levels that meet or exceed strict energy efficiency guidelines set by the U.S. Department of Energy.
Insuring a High Replacement Window Rating
Many people decide to replace their windows when they see a great sale at a local home center store. Generally, the bargain prices are for the bottom-of-the-line windows, which even some well-known manufacturers produce. You're better off avoiding the so-called bargain line. In fact, it can be difficult to find someone to install them because most professionals don't want to be associated with second-rate products. For more on replacement window cost, see our related article.
One final caution: For a window to perform at the levels indicated by the NFRC ratings, it must be installed correctly or you may just be wasting your money. Therefore, choosing a reliable company to handle the installation is extremely important. Be careful and discriminating in hiring a contractor. Look for replacement window contractors who are not only licensed and bonded but also have experience in the specific kinds of work you need done. Get at least three estimates that include itemized cost analysis and particulars about how the project will be carried out. Compare the bids not only for price, but also for what exactly they include. Finally, check referrals.
On the other hand, if you buy the window from the company that installs it, there can be no passing the buck if there are problems since one company is responsible for everything. If you decide to go this route, be sure to check out their window certifications and examine their replacement window warranty before you commit.
When selecting replacement windows, use the NFCR rating and the Energy Star designation to make meaningful comparisons and an informed choice. Be wary of window vendors who won't provide this information. Once you've purchased replacement windows, if you then need to hire installers, carefully compare the credentials of the bidders because your new windows, regardless of their rating, will only be as good as their craftsmanship.