Definition
Window condensation is water that forms on the inside of window glass and frames when warm, humid indoor air touches a surface colder than the air's dew point. Occasional fogging is normal; persistent beading, puddles on sills, or mold on frames signals indoor humidity is too high for the home's window and wall temperatures.
Also called: Condensation on windows, Sweating windows
Why it matters to you
Through long, damp SW Washington winters, everyday moisture from cooking, showers, laundry, and breathing builds up in tighter homes that don't exhaust enough air, and sweating windows are often the first sign. EPA recommends keeping indoor relative humidity below 60 percent, ideally 30 to 50 percent, to limit mold.
Practical guidance
Homeowners can run bath and kitchen exhaust fans, check indoor humidity with a hygrometer, and wipe sills dry. If condensation persists, a technician can check whether exhaust fans work and whether balanced ventilation such as an HRV is needed, while crawlspace moisture problems should be fixed at the source.
About this definition
Written by the Home Energy Group team — a family-owned HVAC company celebrating 25 years of comfort & care across SW Washington and the Portland metro, licensed in Washington (WA LIC# HOMEEGI003J7) and Oregon (OR CCB# 184255). Definitions inform; an on-site diagnosis decides.
