How to tackle condensation

By: Bill Savidan

Waking up to damp windows and walls in your motorhome is no fun. Bill Savidan shares tips on how to avoid this common issue

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Good ventilation of our living spaces, work, home or RV is important. Poor ventilation leads to condensation that can result in unpleasant odours, dampness, mildew and mould. The cause is water vapour that condenses into a film of moisture on cold surfaces.

RVs suffer badly because household volumes of condensation are produced in a space around 10 percent the size of a house. Cooking and showering using steamy hot water in such a confined space loads up the air with extra water vapour. To add insult to injury, each breath we expel is loaded with water vapour as well.

Compounding the problem

Cold weather compounds the problem because we heat our RVs. The warm air carries more water vapour than cold air; this easily accommodates additional steam which condenses back to water on all cooler surfaces and cold areas behind seat cushions, under mattresses and in lockers. This results in outbreaks of mould and mildew.

Turning the heater down at bedtime exacerbates the problem. Cool air holds less water vapour than hot air, so the ‘excess’ vapour condenses back into moisture. Something else is happening as well. In a process known as diffusion, water vapour moves from high concentration places (a boiling pot) to lower concentration places – inside a cabinet for instance, where it condenses into moisture. It’s a continuous process. Like oxalis in your garden, it is always there.

Fighting back

Condensation can be reduced in two ways. One is by having fresh air circulating, i.e. ventilation, and the other is by opening windows and vents while cooking, showering or washing. This removes the water vapour at the source. The cold, fresh air entering your RV holds less water vapour than the steam going out, even if it is raining. Then it’s just a matter of turning up your heater to return to the previous comfort level.

Wherever possible, physically dry surfaces in wet areas, and in the shower, kitchen and vanity basins after use, otherwise evaporation turns this water residue into water vapour, making everything damp again.

Squeegee water down the plughole rather than wiping it up. If a cloth is used to wipe up, wring it out into a basin, down the toilet or, better still, outside. When using drying cloths, hang them up to dry outside so they expel vapour into the air outside, not inside your RV.

Try using a microfibre towel for your initial dry-off after a shower or shave. It dries quicker than a cotton towel and, being smaller, it is easier to find a place outside to hang it up to dry.

Hatches and windows

Improvements made to RV hatches and windows over the past two decades have helped reduce condensation. Fiamma, Dometic Seitz and Remis produce acrylic hatches and windows that have double-glazed acrylic panes to avoid condensation on windows, and ‘plastic’ frames to avoid cold ‘exterior to interior bridges’ where condensation can form.

RV roof hatches are designed to breathe when shut – a useful feature in wet weather and when the RV is stored unattended. Some have electric fans that increase the flow of air through the hatch. These are most effective at clearing steam from bathrooms. When fitted with sensors that monitor temperature, they control the fan speed and keep the interior at a chosen temperature. Hatches fitted with rain sensors close the hatch when rain is detected and opens it when it stops.


12-volt range hoods with single and double speed extractor fans and exterior venting will significantly reduce water vapour levels in your RV. Inverter (heat pump) aircon units for RVs only act as dehumidifiers in the aircon mode. In the heating mode the dehumidifying effect is occurring on the ‘other side’ of the heat pump outside the RV.

RV manufacturers build in permanent vents in doors, stepwells or under the oven to meet compliance standards. Don’t block them. They work with the roof hatches to provide adequate ventilation.

When putting your RV into storage mode, don’t leave the washing up until last thing. Defrost the refrigerator, then open windows and doors and let the RV air properly. Stand seat cushions on edge and open cupboard doors to allow the fresh air to circulate. And don’t leave water lying around in the kettle or the shower tray.
By following these simple housekeeping guidelines, you can avoid condensation putting a dampener on your trip.


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