Building Blocks


The Marling Blog

Windows and Deciphering the Label
Different types and styles of Windows


There are all sorts of styles and options around when you are buying windows, and then there’s the label with more numbers than an elementary school math test. The numbers are measurements of heat, sunlight blockage, light transmission and air leakage. They allow you to pick the most efficient window from the styles you can chose from. The sales staff at Marling locations can help you navigate your way through styles and efficiency.

General Information

Four basic materials are used to frame the glass in windows and each has its pros and cons.

Vinyl is a poor thermal conductor so it’s a good insulator, but it’s not the most attractive option. There are limited color choices in vinyl and trying to paint it another color is usually disastrous.

Fiberglass accounts for only about 3% of the window market. It’s durable, practically maintenance free - but double the cost of vinyl.

The biggest advantage to aluminum is that it is strong so the framing and sashes are thinner than other window options. There is also a large variety of factory finishes for aluminum windows. But, it’s a poor insulator against both heat and cold. Expansion and contraction from temperature changes causes a lot of stress on the seal between the glass and the frame.

Wood has natural beauty and warmth going for it, but it is susceptible to rot and insect damage. It’s a great insulator and takes stain and paint well. In climates with temperature variations, wood windows require almost constant maintenance.

Styles and Other Options

There’s standard, double-hung and casement windows that you see most often. There are also awning windows. These are hinged on the top and they swing out on the bottom. Jalousie or louvered windows have glass slats that open and close. There are chronic seal issues with this style and they are not recommended for severe climates.

Glass block windows are individual glass or acrylic blocks sealed into a unit and then placed in vinyl or aluminum frames. Originally just used as privacy windows in bathrooms, they now come in a variety of styles and are gaining in popularity.

Showing up as prototypes or available for just commercial applications are windows that are sunlight and temperature sensitive.

What Does that Label Mean?

Your window likely has two labels. One is the Energy Star label and the other is the National Fenestration Rating Council label. The Energy Star label shows that the window meets energy efficiency guidelines established by the U.S. Environmental Protection Agency. If you go to, there is a map that shows what you should be looking for in the area where you live.

The NFRC label shows what performance standards the window meets. This label rates the window’s U-factor, solar heat gain coefficient, visible transmittance and air leakage. It looks complicated, but it’s not really that hard.

The U-factor is the window’s insulation value and the solar heat gain coefficient shows how well the window blocks heat transfer into the house from sunlight outside. Look for a U-factor between .20 and 1.20 and a solar heat gain coefficient from 0 to 1. The lower that number is means less dollars going to cool your home. As an aside, to claim federal tax credits on your windows, the U-factor and solar heat gain coefficient must both be less than or equal to 0.30.

Visible transmittance should be between 0 and 1. This measures how much light is allowed into the home through the window.

Air leakage is pretty self-explanatory - the air infiltration that the window permits. It should be between 1 and 3.

Both the Janesville and Madison Marling locations have examples of different styles and types of windows. The sales staff can help you find what you need and guide you through the options. Contact us here to learn more.

These are the window brands Marling carries:

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