Moisture & Health• 9 min read
The Homeowner's Guide to Condensation Prevention: Physics, Ventilation & Glazing
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Authored by Dr. Evelyn Vance • Updated on 2026-04-26
Master Step-by-Step Action Plan
1
Measure Indoor Relative Humidity
Use a digital hygrometer to maintain 35%–45% RH in winter.
2
Utilize Mechanical Ventilation
Run bathroom and kitchen exhaust fans during and after moisture generation.
3
Upgrade to Warm-Edge Glazing
Eliminate cold perimeter aluminum spacer thermal bridges.
4
Ensure Unobstructed Warm Air Flow
Open interior blinds 1 inch at night to allow warm air convection against glass.
## Eliminating Window Condensation & Sill Mildew
Condensation is the physical reaction that occurs when warm, moisture-laden indoor air comes into contact with a cold window surface below the air's dew point.
### The 3-Step Strategy to Eliminate Condensation:
1. **Reduce Source Indoor Moisture:** Vent clothes dryers outside, run exhaust fans for 20 minutes post-shower, and avoid unvented kerosene heaters.
2. **Increase Air Circulation:** Ceiling fans running clockwise on low speed in winter circulate warm ceiling air down across exterior window glass.
3. **Upgrade to High-Performance Windows:** Insulated double glazing with non-conductive composite spacers keeps interior glass temperatures above 58°F, preventing condensation.
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