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Where do you live? Is it cold or hot, wet or dry, or something in between? I live in an area that is considered cold and moist, Northern Minnesota. My climate is much different than Tucson, Arizona or Kansas City, Missouri. Because of the climate differences, some of my choices in building materials will be different, including my choice of windows. Windows should also be chosen with local climate in mind.
In this piece, I’ll help you understand how climate affects code, what measures you should look at when assessing windows for your climate, and how window selections can improve performance.
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Understanding heat loss in cold climates
Building codes will require better insulating properties from windows in cold climates, than in warm climates. To understand how well a window keeps heat from escaping, you need to look at its U-Factor value.
U-Factor values measure the rate of energy (heat) loss. These values are listed differently than what you might be familiar with if you're aware of R-Value, which measures resistance to heat flow. With R-Value, the higher the number, the better the insulation performance. With U-Factor, lower numbers are better because it’s a measure of how fast heat moves through the window assembly, which means it’s the inverse of R-Value. U-Factor values are between 0 and 1 and will almost always be a decimal point.
Here’s what the IRC lists for U-Factor values in each climate zone:*
- No U-Factor requirements in climates zones 0 and 1
- 0.40 or lower in climate zone 2
- 0.30 or lower in climate zones 3 through 8
* Based on the 2021 IRC table R1102.1.2 (R402.1.2))
In addition to the product’s performance label, you can find U-Factor values for Andersen products by working with your local dealer or by looking up Andersen products in the NFRC Certified Product Directory.
