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Choosing a High-Performance Window

The amount of clear glass windows in America could exceed 100s of millions of square feet. The major part of this housing stock is at least 30 to 40 years of age. So one could imagine the market for new windows is a large industry, with many manufacturers. The good news for consumers, window manufacturers must label their windows. If you happen to come across a window with no label, just say no thanks. This will take you on a tour of window labeling to guide you in your choice of window product.

So let me say a few words about what’s not on the label. Which window does a better job insulating a single pane window versus a double pane window? It’s pretty simple, the air space between the double panes of glass adds to the insulating performance. How about a wood frame versus aluminum frame window? Metal conducts heat or cold much faster than wood; metal expands and contracts more than any other type of window. Most metal window frames are used in commercial applications. The coatings on gas adds to the cost of a window, primarily labeled as Low-E coatings. Many windows on the market are filled with gases which increase the R value of a window.

Let’s get down to the labeling

Parts of a window and what is all means. First, a quality window manufacture will label a window as certified by the NFRC, this is the National Fenestration Rating Council. This is a joint collaborative effort between manufacturers and the Department of Energy. This label gives you performance based on the whole window, not just the glass. For example, a clear piece of glass has a Visible Transmittance of .9 or a VT factor of .90, a number of 1 would represent 100% of light passage through the glass. That being said, in window production there are frames and sashes which drops the VT rating of a window, this rating includes 100% of all materials used in the window.


Interpreting the NFRC Window Label


U-Factor measures how well a window product prevents heat from escaping through a window. The lower the U-Factor the greater the window resistance to heat flow. This also includes the insulating factor of a window.

Solar heat gain coefficient (SHGC)

SHGC measures how well a window blocks heat from incoming sunlight. It is rated between 0 and 1. The lower the number the less solar heat is transmitted through the window. In the southern part of the country, this has a larger impact in energy cost.

Visible transmittance (VT)

VT measures how much light passes through a window.

Air leakage (AL)

is a measure of infiltration through cracks in the window assembly. This number is expressed in the cubic feet of air passing through a square foot of window space. Typically, the lower the number the better.

Condensation resistance (CR)

CR measures the ability of a window to resist the formation of condensation on the interior surface. This number is between 0 and 100. The higher the number the better the window prevents water formation.

Choosing windows based on home orientation:

You won't be getting any solar heat gain on the North facade, so go with the highest R-value your budget will allow.

The South facade of the house is where your pay off is! Choosing a set of windows based on Solar heat gain coefficient, you will gain more heat in the day than you will lose at night, by as much as 50%. Its OK sacrifice some R-value by way of Low E coatings to increase the solar heat gain from the low winter sun. You should choose a high SHGC with the highest possible R-value, don't get cheap here.

And remember that the frame of your window can take up as much as 20% of your total window area. Be sure to choose the correct window glazing: a high coefficient of visible transmittance [VT] and ensure that glazing on all orientations have a matching color or tint. A high VT means more daylight is available which can save energy for artificial light and its associated cooling load.

The Pella Difference

Pella Window and Doors Manufactured In the USA for Over 85 Years!

Pella has been focused on bringing homeowners beautiful, innovative, and energy efficient windows and doors since 1925. You can choose their products with confidence knowing that all are built and backed by a strong, family-owned American company.

More choices means Pella can fit your style and budget

Pella offers more windows, patio doors, and entry door choices than any other leading brand. A variety of materials, price ranges, and style options means you can own the quality Pella window or door you want without paying for features you don't.

Award-Winning Energy Efficiency

Pella Corporation was one of the winners for the US Department of Energy's Energy Star partner of the year award in 2013. Pella has been recognized as an Energy Star partner of the year 6 times in recognition of a commitment to delivering and promoting the use of energy efficient products.

Service and Satisfaction Year After Year

When you choose Pella windows and doors, you get service from Pella professionals who are dedicated to your satisfaction. Whether you just started thinking about windows for your new home or have a question about a Pella product you bought 20 years ago, just give Pella a call.

Three material choices means Pella has the right one for you

Unlike other window companies, Pella doesn't believe that one material fit all. After all, windows and patio doors are too important not to have a real choice in their design. That's why Pella offers you windows and patio doors made from three different material types; there is one sure to fit your home, your needs, and your budget. Here's a quick overview of each material and its unique advantages.


Wood offers unparalleled beauty, warmth, design flexibility, and can be painted or stained. Strong wood frames with aluminum-clad exteriors arrived with the added protection of durable low-maintenance and clad finish. Exceptionally energy efficient and comfortable, wood window frames insulate more than 1800 times better than aluminum window frames. Pella's exclusive Endura-Guard wood protection provides strong protection against the effects of moisture, decay, and stains from mold and mildew.


Exceptionally strong and durable, withstands extreme heat and cold. Outstanding performance, the look of painted wood, and has minimal maintenance. Highly energy-efficient, provides the insulating properties of wood.


Attractive interiors and exteriors that stay looking great for years. Easy-care vinyl frames means no more painting, staining, or refinishing. Energy efficient, high-quality, multi-chambered vinyl reduces heat loss.

Cabernet Design and Builders Are Factory-Trained Pella Window and Door Installers