Reading U-Factor and Energy Labels
Every new window carries a label with performance ratings. A few numbers tell you how it will handle a Des Moines winter.
Request a window quoteU-factor
Measures how much heat escapes. Lower is better; in a cold climate like Iowa's, it's the most important number.
Solar heat gain
How much sun heat comes through. In the north, moderate values let in winter sun.
Visible transmittance
How much light comes through. Higher means brighter rooms.
Air leakage
How much air passes through the window. Lower is better.
ENERGY STAR zones
Look for windows rated for the northern zone.
Compare the same size
Ratings are for standard sizes, so compare like with like.
Glass packages
Low-E coatings, gas fills and warm-edge spacers change the ratings.
Ask for the labels
Ask the company for spec sheets for each product quoted.
Next
See replacement windows.
Condensation resistance
Some labels include a condensation resistance rating. Higher numbers mean the glass and frame are less likely to sweat on cold mornings, which matters in a Central Iowa winter.
More window replacement guides
Drafty, foggy or hail-damaged windows?
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