Relative humidity of 25%-60% is generally comfortable for humans.^{1) 2) 3)}

Excessive humidity is a common challenge for vandwellers. It can cause mold/mildew, damage to electronics from water condensate, discomfort, wood expansion, and diminution of insulative properties of items like sleeping bags.

Common causes of high humidity / condensation include:

Humidity due to constant habitation can be reduced with increased ventilation, as with roof vent, assuming exterior humidity is lower than that of the interior.

Window vents can be used to crack windows without allowing rain in.

A “sacrificial window” may work as an unpowered option.⁴⁾

Relocation to a drier climate sounds like a severe response, but snowbirds often follow comfortable weather.

Humidity due to use of propane or butane can be reduced with increased ventilation, reduced cooking/heating times, and the use of more efficient propane appliances to reduce overall consumption.

Water vapor is often released during cooking, most visibly during a boil. Methods to reduce the production of water vapor include:

• covering anything that steams: pots, cups, etc.
• reducing beverage temperatures if appropriate - coffee requires near-boiling temperatures but most other hot beverages do not. Green tea is generally steeped at 160F and black tea at 190F.
• reducing food reheating temperatures if appropriate. Already cooked commercial foods (canned or bottled foods) do not need to be boiled.
• reducing water temperatures for drinking water sanitization if appropriate. Boiling is the traditional method but this has more to do with knowing the water temperature without a thermometer. For comparison, milk is pasteurized at 161F for 15 seconds or 145F for 30 minutes.⁵⁾ Enteric bacteria, spores, and viruses are killed by sufficent time at 160F.⁶⁾ If using boiling as a reference point, merely bringing the water to the boiling point is more than sufficient and holding the boil is “excessive”.⁷⁾ There is nothing magic about boiling.

Products containing calcium carbide (DampRid, etc) or silica gel (Eva-Dry, etc) may help control excessive moisture, particularly in very small or confined areas. Some silica gel units can be “refreshed” by plugging them into a 110v socket whenever the color indicator advises. This gently heats the gel and drives off the moisture, so do this somewhere other than your camper!⁸⁾

Eva-Dry units are named after the cubic feet of space they are designed to handle. Example: the E-500 is made for 500 cubic feet, approximately 8x8x8'. Units larger than 500 are peltier or some other non-chemical technology.

In some cases an electric dehumidifier may be necessary. Bitty recommends the Eva-dry Edv-1100.⁹⁾ Some users drain the receptacle into a sink or other drain.¹⁰⁾ Eva-Dry confirms the 12v adapter for this model passes 12v and not 9v;¹¹⁾ this should make it easier to wire from house power.

Peltier devices are power-hungry and run constantly; the dehumidifier might best be used as an opportunity load.

Video: teardown of a typical peltier dehumidifier

In some very dry regions humidity may be too low (=<20%)for comfort. Evaporative coolers or ultrasonic misters may help improve the interior humidity.