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condensation in tents


  • water condensation can be problematic for campers as it may:
    • form condensation on the outside of the tent which not only makes it wet but the moisture can sometimes wick inside if one touches the inner surface
    • form condensation on the inner surface of the tent mainly from poorly ventilated exhaled humid air which then drops back onto the camper's sleeping bag and clothes making them wet and cold
    • if frost forms it may stop your zippers working until it melts
  • too little ventilation can make the camper and their sleeping bag/clothes cold and wet
  • too much ventilation on cold nights reduces camper comfort from:
    • wind chill on exposed skin
    • lower inspired air temperatures - when this drops below 10degC the risk of cold-induced bronchopspasm with coughing or asthma attacks is increased.
  • bring a spare towel to mop up any troublesome condensation

The science of condensation

  • when air temperature drops below its dewpoint temperature, water will begin to form dew or condensation on the colder surfaces where there is a colder layer of that air and if this temperature falls below zero degC then it becomes frost (in air it becomes fog or cloud).
  • the dewpoint is a measure of the amount of water content in an air mass and its measurement is mainly determined by the temperature of the air mass and it's relative humidity (RH) - the greater the RH, the closer the dewpoint comes to the dry bulb temperature.
    • dewpoint = dry bulb temp - (100-RH)/5) and thus RH = 100 - 5(dry bulb temp - dewpoint)
  • exhaled air contains 0.034g water per litre air (at 37degC, 1 liter of air is full saturated at 0.0436g water content) and generally has a temperature in the range of 31.4-35.4 °C and a RH of 40-100% (not always 100% as many state)1) and this results in some 100-150mL of water being exhaled into the tent overnight per person.
    • at 33degC and at 80% RH, the dewpoint will be approx. 29degC so it is easy to see that this is a major risk for condensation as most nights have air temperatures well below 29degC
    • if this exhaled water is not vented outside (eg. a fully sealed fabric inner canopy of a tent), the RH of the tent will increase quickly and the dewpoint will approach the tent temperature which will generally be much warmer than the outside air temperature. This will inevitably result in condensation on the inside of the tent fabric as this will be cooler from the outside air.

Preventing condensation inside tents

camping site selection

  • camping close to a water body such as a river or lake, particularly in a region where night temperatures fall significantly and there is little wind to keep the air near the fly moving is a recipe for lots of condensation on the outer and inner surface of the fly as RH is higher and the temperature is more likely to fall below dewpoint overnight
  • high humidity days or regions are also likely to increase risk (and also prolong the ability for the tent, towels and clothes to dry out during the day

tent design and camper management of ventilation

  • condensation is particularly a problem for single wall tents (most hiking tents are dual wall - inner canopy and a fly)
  • the prime method is to ensure there is adequate ventilation of external air passing through the inside of the tent and then venting (preferably near the ceiling
  • mesh tent design with the inner tent “canopy” made mainly of mesh will theoretically have the best ventilation and least amount of condensation issues however:
    • if the fly is not well ventilated, water can condense on its inner surface and drop back through the mesh onto the camper
    • this mesh design has the greatest wind chill on the camper hence many tents have a fabric bottom half and a mesh top half as a compromise
  • mainly fabric inner tent design should allow the camper to vary the degree of ventilation depending on conditions as:
    • they may prefer to reduce ventilation for some time to keep themselves warm
    • wind chill inside is an important comfort factor at night and this relates to the outside air temperature and the speed at which it passes over the camper
      • most tents are designed for the outside air to enter UNDER the fly (or through an open vestibule doorway) then pass upwards to escape through a ceiling vent
        • this will usually suffice to keep the inner surface of the fly dry but becomes more complex for the inner tent “canopy” when this is mainly fabric such as nylon rather than mesh.
        • in these situations, the camper will need to open (preferably insect proof meshed) vents to ensure adequate ventilation of the inner tent canopy and to minimise wind chill on the camper, the entry vent for the inner canopy is often high such as the top part of the door and the exit vent is either high on the opposite door or a ceiling vent.
australia/tent_condensation.txt · Last modified: 2021/04/16 14:04 by gary1