CSLB General Building (B)Finishes and Building EnvelopeEasy
A homeowner is comparing replacement windows and notices one has a lower U-factor than another on its NFRC label. What does this indicate about the window's performance?
- AIt blocks more solar heat gain in summer
- BIt allows more visible light into the room
- CIt resists heat transfer better, improving insulation
- DIt has a higher air infiltration rate
Show answer & explanationAnswer & explanation
Correct answer: C. It resists heat transfer better, improving insulation
U-factor measures the rate of non-solar heat transfer through a window; a lower U-factor means less heat escapes or enters, indicating better insulating performance, which is unrelated to visible light transmittance, solar heat gain coefficient, or air leakage ratings.
Why the other options are wrong
- A. Solar heat gain coefficient (SHGC), not U-factor, measures solar heat blocking.
- B. Visible light transmittance (VT) is a separate NFRC rating, not U-factor.
- D. Air leakage is a separate NFRC metric measured in cfm/ft².
U-Factor
An NFRC rating measuring the rate of heat transfer through a window assembly; lower values indicate better insulating performance.
- Lower U-factor = better insulation
- Different from SHGC (solar heat gain)
- Required on all NFRC-certified window labels
Memory trick: 'U for you staying warm—lower is better.'