Window ratings measure all types of things about a window.  Taken together, they tell a story about the value of the window, in terms of strength, durability, and most certainly energy efficiency.

But looking at all of these ratings and valuations can be a little overwhelming.  That's why we've created a list of common window values, and explained in simple terms what they measure, and how to read them. 

Here are the most common window ratings:

U-Factor

• The lower the U-factor, the better.
• The lower the U-factor, the greater a window's resistance to heat flow and the better its insulating value. It is a number between 0 and 1.
• Industry standard windows usually have a U-factor of 0.30 or lower.

Design Pressure (DP)

• The higher the DP, the better.
• The design pressure measures the strength and resiliency or a window, specifically how much pressure it can withstand without suffering breakage or damage.
• The higher the number, the stronger the window, the less air infiltration, and the longer it will perform to specifications.

Air Infiltration

• The lower the number, the better.
• A measure of air leakage per minute around a window, which is expressed as cubic feet per minute, or CFM. The lower the CFM, the better its air tightness.
• Industry standard is 0.30 CFM or lower.
• One CFM equals 7.5 gallons of air per minute leakage.

Water Penetration

• The higher the number, the better.
• Measures the ability to withstand water pressure in pounds per square foot, or PSF.
• Industry standard is 4.0 PSF or better.

R-Value

• The higher the number, the better.
• The R-value is simply the inverse of the U-factor. Meaning the R-value = 1/U-factor.
• As in the U-factor (above), this measures heat conductivity.

Solar Heat Gain Coefficient (SHGC)

• The lower the number, the better.
• The fraction of solar radiation admitted through a window, both directly transmitted, and absorbed and subsequently released inward.
• Expressed as a number between 0 and 1.
• The lower the SHGC, the less solar heat it transmits.

Visible Transmittance (VT)

• The lower the number, the more light the window blocks.
• It is the fraction of light transmittance through the window, measured between 0 and 1.
• Personal preference and circumstances my determine the desirable VT for you.

Condensation Resistance

• The higher the number, the better.
• Measures how well the product resists the formation of condensation.
• Expressed as a number between 1 and 100.

Of course, every home is different.  If you are shopping for replacement windows in Cincinnati, give Windows Plus a call.  We'll go over these numbers in detail, and help find the right vinyl window for your home.

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