What is condensation?

Condensation is the accumulation of water vapor changing to liquid water onto a surface. When the interior temperature is warmer than the window surface, there is a chance that condensation will form. As the outside temperature decreases, the inside of the window surface will drop, causing the interior window surface to be between the exterior temperature and the interior temperature. Since it is not possible to control the exterior, the interior conditions must be controlled in order to prevent condensation.

What is dew point?

The dew point is the temperature at which water vapor in the air will condense into liquid water. The dew point temperature will change depending on the inside temperature and relative humidity. When any surface temperature falls below the dew point, water will condense on the surface, such as a cold can of soda or a glass window.

What is relative humidity?

Relative humidity is the ratio between how much water vapor is in the air and the maximum amount of water that can be held in the air. The maximum amount of water vapor that air can hold varies with the temperature of the air. As the temperature of the air increases, it is able to retain more water vapor. When the interior air comes in contact with the colder window surface the air temperature drops and it is unable to hold as much water, this causes the excess water to accumulate onto the window surface.

How do I prevent condensation?

In order to prevent condensation, humidity in the room must be controlled. As the exterior temperature is colder, the humidity inside must be lowered as well to prevent condensation. To lower condensation, dehumidifiers can be used and are one of the most effective ways to control humidity. Environmental conditions that lead to condensation formation are often temporary. These causes include: extreme cold outside temperatures, cooking, showering, and clothes drying. If the formation of condensation is more than a temporary condition, an HVAC expert should be consulted to evaluate the relative humidity within the room and/or building

What should my relative humidity be to prevent condensation?

Based on Engineering Studies at 70ºF conducted at the University of Minnesota Laboratories, the American Architectural Manufactures Association (AAMA) suggests that humidity levels not exceed the values referenced in the below table to prevent condensation.

Outside Air Temperature Inside Relative Humidity -20ºF or below Not Over 15% -20ºF to -10ºF Not Over 20% -10ºF to 0ºF Not Over 25% 0ºF to 40º Not Over 30%