Indoor Condensation
Last Updated: August 1, 2024
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Indoor Condensation
Indoor Condensation
Share via E-mailIndoor condensation on windows occurs when moisture in the air meets the cooler surface of the window glass, causing the water vapor to condense into droplets on the room-side glass surface. This usually happens when the indoor air is warm and humid while the window surface is cooler, usually due to cold outdoor temperatures.
Indoor condensation is influenced by factors such as indoor relative humidity (RH) levels, room-side glass surface temperatures, indoor air circulation, and the temperature difference between the inside and outside of the home. Excessive indoor condensation can cause issues with ventilation, and if persistent, may lead to problems like mold growth, health problems, and can damage window frames and surrounding materials.
Maintaining a Desirable Humidity Level
People are most comfortable when relative humidity ranges between 20% and 60%. In the home, an average relative humidity of 35% to 40% is appropriate when the outside temperature is 20 °F (-7 °C) or above. However, during cold weather, higher humidity ranges may cause indoor condensation on windows.
The table below shows recommended indoor humidity levels in relation to outdoor temperatures.
| Outdoor Temperature °F | Recommended Relative Humidity |
|---|---|
|
20° and Above |
35% to 40% |
|
+10° |
30% |
|
0° |
25% |
|
-10° |
20% |
|
-20° |
15% |
Figure: Recommended indoor humidity levels
The table below shows the relationship of condensation to indoor glass and room relative humidity. If glass conditions are above the line in the chart, expect to see condensation. If they are below the line, you won’t see condensation.
Relative Humidity (%)
Temperature (°F)
Figure: % relative humidity vs indoor glass surface temperature
How to Limit Indoor Condensation
- Control humidity levels in the home. The U.S. ENERGY STAR® program advises maintaining 30-40% relative humidity in colder climates to limit potential of indoor condensation. Steps to achieve this may include limiting the use of a humidifier and increasing indoor air circulation by using ventilation to remove excess humidity, especially in areas like the kitchen, bathrooms, and other moisture-prone places.
- Select window glass that maintains higher glass surface temperatures. Choosing Cardinal LoĒ™ coatings in an IG unit with a warm-edge spacer helps maintain warmer glass surfaces, reducing condensation potential. For maximum condensation resistance, use triple-pane IG with LoĒ coatings.
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