Wednesday, March 23, 2011

Guest Columnist Dowd Discusses Choosing the Right Windows in Different Climates

In this installment, Dean Dowd, Chief Technology Officer for National Fenestration Rating Council (NFRC) member company, CalFinder, discusses how to choose the right windows for your climate.

By Dean Dowd

Which Types of Windows are Best for Your Climate?

To save money on your energy bills with new windows, you must first find the appropriate match for your climate. This may seem like a straightforward concept, but you’d be amazed at how often homeowners replace their windows with ones that are totally unsuitable for their local weather.

And you know what that leads to: untold heating and cooling dollars out the window (quite literally in this case). So in this week’s article, we’ll focus on how to reduce your energy bill by finding the best windows for your own climate. Here’s how to go about it.

Know Your Zone

First things first. To find the right replacement windows, first double-check your climate zone. Energy-Star, a government-sponsored energy-efficiency initiative, divides the United States into four main climate regions: Southern, South-Central, Northern, and North-Central.

Locate your zone using the map
available here.

Homes in the Northern zone will benefit the most from windows rated with a U-factor of 0.30 or less and an SHGC of 0.35 or greater. Those in the North-Central zone (Kentucky, for instance) will perform best with a U-Factor between 0.28-0.32 and an SHGC of less than 0.39.

For the Southern zone, consider a window that has a rating of 0.60 or slightly less, and an SHGC of 0.25-0.27. Finally, homes in the South-Central zone (MS, for example) will get the best efficiency from a U-Factor 0.25-0.35/SHGC 0.30 or less-rated window.

Choosing the Right Window the First Time

NFRC rates and labels most new and replacement windows made. These labels contain pertinent data on window energy efficiencies, such as:

• The U-Factor, or how well the window insulates against heat loss. A U-Factor of 0.20 is generally the most insulating and 1.20 the least.

Air Leakage (AL), which describes the level of air that escapes or enters via the tiny crevices in a window frame, is measured by cubic feet per square foot (cfm/sq ft). The lower the AL, the less air that passes through the frame.

Solar Heat Gain Coefficient (SHGC) is how well a window blocks the radiant heat in sunlight. It is a number between 0 and 1, with the lowest number being the most ideal for keeping the most heat out.

Knowing these factors (among other pertinent but sometimes optional ratings), it’s important to realize that all windows leak heat come winter and allow it in the summer. With a highly energy-efficient window that’s mated properly to its climate, though, the leakage will be virtually non-existent.


Looks like a random bunch of numbers and confusion by now, huh? It's not. In addition to the information on this site, your contractor (given that they’re knowledgeable and up to date on window product ratings) should know your local climate and which type of window works best almost by heart.

So let's here about your experience. Has anyone found the NFRC label helpful in choosing the right kind of windows for their climate zone?