Condensation

The cold, hard facts of life.


It happens. Sometimes, condensation is unavoidable, however, there are ways you can mitigate it. Understanding how and why condensation forms will help you to make informed decisions when pitching your tent. Skip to the bottom for some pointers.


Terminology

Condensation:

The transition of water vapor into liquid water. This occurs at the dew point.

  • On solid surfaces, condensation is experienced as water droplets forming on the surface (dew). In the air, water will condense onto tiny particles of dirt in the air (fog).

Humidity:

A measure of the amount of water vapor in the air.

Relative Humidity:

The amount of water vapor in the air compared to what the the air can hold at a given temperature.

  • At 100% relative humidity, the air cannot hold any more moisture at the given temperature.

Dew Point:

The temperature at which air becomes saturated with water vapor. At the dew point, water vapor condenses to liquid water.

Causes of Condensation

Drop in Air Temperature

Air temperature often falls at night. When it drops to the dew point, condensation will begin forming on tiny dirt particles suspended in the air.

  • When air cools to the dew point by contact with a colder surface (aka tent wall), water will condense on that surface

Drop in Surface Temperature

Surface temperatures drop due to convective and radiative heat loss. When surface temperatures fall below the dew point, condensation will occur on the surface as the passing air is cooled to the dew point.

  • Convective heat loss occurs as cooler air travels over a warmer surface, carrying some of the warmth away with it.
  • Radiative heat loss occurs when an object loses heat in the form of electromagnetic radiation to cooler surroundings. This means surfaces (like your tent walls) radiate heat to the colder overall temperature of the cosmos (a clear sky). Cloud and tree cover can act as a blanket, reducing radiative losses.

Increase in Humidity

If the amount of water vapor in the air increases while the temperature remains the same, the relative humidity will increase. If it reaches 100%, condensation will occur.

  • As a person breathes and perspires, water is lost from the body to the surrounding environment. In a semi-closed environment like a tent, this increases the humidity locally. Body heat will help to raise the air temperature inside the tent, however surface temperatures do not change significantly. If the humidity increases enough relative to the temperature of the tent wall, condensation will form on the interior of the tent.

Mitigating Condensation

Increase ventilation

Pitch your tent with ventilation in mind.

  • For our Cirriform, orient your shelter with the head wall into the wind for maximum airflow.
  • If it's not raining, keep the beak/vestibule open and tied back.
  • If it is raining lightly, you can keep the beak/vestibule partially open and tied back.
  • Use the secondary zipper pull at the top of the zipper to partially unzip the top. Use the prop to spread the zipper and increase venting.

Site Selection:

Remember the 3 S's

  • Surface: Avoid pitching your tent on grass or ground surfaces containing moisture. Doing so will increase the humidity under the fly.
  • Sky: On clear nights, avoid pitching under open sky. Opt for tree cover to minimize radiative heat loss.
  • Surroundings: Avoid camping near water (increases humidity) and in locations where cold air may sink and collect at night.