How to Understand Window Ratings

So you're shopping for replacement windows, and you keep hearing all different types of numbers and figures being thrown around about them.  From energy efficiency to strength ratings, these things can get overwhelming.  

So what I've put together is a straight-forward guide to window ratings.  What they are, what they mean, and how to read them (is a lower U-factor better, or a higher one?).  

So here are the most important 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.

I hope this helps.  If you have any questions, please feel free to leave a comment below.  And as always, if you're interested in talking to the best replacement window company in Cincinnati, you can reach out to me directly by giving Windows Plus a call.  

Thanks for reading!

Mike G.

The Window & Door Guy