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Smart Guide to Windows

There's a new breed of energy-efficient windows on the home building scene. Here's how they stack up.
by Donna Peak

If you're looking for the one area to "green" up your log home, the answer is clear as glass. In fact, it is glass. Windows can be either the biggest source of heat loss (an average home may lose up to 30 percent of its conditioned air through poorly insulated windows) or an effectual way to save energy and money, depending on what you choose. Before the mid 1980s, most log homes had inexpensive, single-glazed (meaning one sheet of glass) windows; the insulating factor translates to the equivalent of R-1, which is about the same as having gaping holes in the sides of your home—not very effective at all. Soon, double-glazed windows that employed two layers of glass with an air pocket trapped inside hit the home-design scene. Though these are a better option, they're still not the greatest insulator.

With energy costs soaring and environmental stewardship on the forefront of many people's minds, windows have finally come into their own. Manufacturers have made huge strides with their products, and today's windows can boast upwards of R-7 to R-14 ratings. These new products come with a lot of new lingo that can be difficult to decipher as you window shop. Here, we'll demystify some of that jargon to help you make the smartest choice for your log home.

Low-E WindowLow-E Window
What it is: Glass treated with an insulating metal-oxide coating
How it works: Light is transmitted in different wavelengths. The transparent coating lets most of these wavelengths through, however, in the lower part of the spectrum where infrared is located, the coating acts like a mirror, reflecting infrared light back toward the warm side of the window. In cold climates, the low-e coating should be placed in a home's interior to keep warm air in. Conversely, in temperate to warm regions, the coated side of the window should be placed outside to keep heat from infiltrating the house.
Bonus feature: Because it blocks UV rays, it helps keep fabrics from fading.
Energy value: Up to R-3 (U-0.33)

Gas-Filled WindowGas-Filled Window
What it is: Multi-glazed window filled with a gas insulator
How it works: A double- or triple-glazed window is certainly more energy efficient than a single sheet of glass, but the empty air pockets created by multiple glazing can create a convective loop that may actually lower the window's efficiency. Pumping these cavities with a heavier-than-air gas, such as argon or krypton, "fills" the pocket, preventing heat transfer and insulating the window.
Energy value: R and U values vary depending on the number of layers and the type of gas fill used.

Heat-Mirror® WindowHeat-Mirror® Window
What it is: A registered trademark for a technique combining high-transparency plastic suspended between two panes of glass.
How it works: In essence, the film creates an extra "layer" of glazing and provides more surface area for low-e coatings, resulting in improved performance. Because of the additional insulating properties it provides, it boosts the energy performance of a traditional log home staple—a wall of windows—meaning the window wall neither will make the home uncomfortably hot in the summer nor cold in the winter.
Energy value: Up to R-7 (U-0.14)

Super WindowSuper Window
What it is: A combination of advanced, energy-efficient features
How it works: By integrating multiple layers of glass with other energy-efficient measures such as low-e coatings and gas fills and securing them with insulated-fiberglass frames, manufacturers have been able to craft windows that mimic the R values of solid, insulated walls.
Energy value: Up to R-14 (U-0.07)

Published in Country's Best Log Homes
Comment Feed

2 Responses

  1. On gas-filled windows: the argon has a higher resistance to heat transfer (higher R value) than air, thus providing better insulation than an air-filled void. With any multi-ply fenestration, if the seal between panes of glass is compromised, not only will the gas inside leak out, but moisture can get in, thus creating fogging of the window.

    Joseph MackJuly 13, 2009 @ 12:02 amReply
  2. Downside to low E windows is that your indoor plants will not grow, some will die due to the reduced rays. Window shops will not tell you that.

    Rich VolantFebruary 8, 2013 @ 11:20 pmReply

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