Determining the Dew Point

To determine the dew point, use the following tables: first, find the desired air temperature on the left side of the table. Then, locate the relative humidity of the air at the top of the table. The intersection of these two values in the matrix indicates the temperature at which the dew point occurs.

When air comes into contact with a surface whose temperature is equal to or lower than the dew point, condensation (moisture) forms on that surface.

Example: If the air temperature is 75°F (24°C) and the relative humidity is 35%, the intersection of these two values shows that the dew point occurs at 45°F (7°C) or lower. This means that the water vapor in the 75°F air with 35% relative humidity will condense on any surface with a temperature equal to or lower than the 45°F dew point.

This example can represent the inside of a building, where the temperature is 75°F and the relative humidity is 35% during the day. At night, the outside temperature drops. While it is unlikely that the indoor air will cool from 75°F to 45°F, there is a high probability that the building’s structures and exposed surfaces will reach the dew point temperature, leading to condensation.

Air temperature in degrees Celsius

Example: Read the air temperature from the left column and the relative humidity from the top of the chart. If the storage unit temperature is 75°F (24°C) and the relative humidity is 35%, the intersection of these two values shows that the dew point in that area is 45°F (7°C). If the metal coming in has a temperature lower than 45°F (7°C), water will condense on the metal.

Air temperature in degrees Fahrenheit