Condensation

Condensation is a matter of fact, it’s part of life, it’s physics and as Scotty will always tell you, ‘You cannae change the laws of physics!”

So what is it? Simply put it’s when a gas turns to a liquid. The gas is warm air, the catalyst is a cold window, the result is gas turning to liquid ie: water. The warmer the air the more humid it is, the more water it contains, therefore the more condensation when the warm air and cold surface meet. The opposite of condensation is vapourisation, when a liquid turns to a gas. ie: water to humid air.

 

A DryBag and a silica crystal canister.
A DryBag and a silica crystal canister.

Condensation in a motorhome is of course unwanted as damp over time can lead to mould and can even affect the structural integrity of the wood frames inside, rot fabric and corrode metals. To try to minimise this happening the air humidity needs to be lowered, and/or ventilation in the van needs to be improved. You can do this simply by opening windows, using extractor fans but these tend to be power hungry, using dehumidifiers -and although there are some 12 volt dehumidifiers on the market, there efficacy is minimal- and using static dehumidifiers such as canisters of silica crystals, containers of salt based crystals and bags of moisture absorbing sand.

Of course not having damp clothes inside, covering pans and opening windows while cooking can help. A window is best left open when sleeping too as we give off large amounts of moisture as we breathe, it’s something like a half a litre per day. Constant ventilation is by far the best enemy of condensation but you could use some of the other methods mentioned to help you out.

 

 

 

  • The containers of crystals are relatively inexpensive but they are best used in static vans or vans that are in storage. The moisture in the air is attracted to the crystals and collects in a container underneath. These are very easy to spill when moving so are counterproductive for a van that is being used.
  • Some crystals are based on silica gel so as they absorb moisture they simply expand, these are effective but need to be replaced regularly.
  • 12 volt dehumidifiers don’t use a lot of power but they are an additional drain on batteries and they collect very little moisture. Also they’re quite bulky so it’s difficult to place them in small corners and places where condensation is worst.
  • The method I use is called DryBags. These are bags of a sand type material that absorbs moisture and you can see the material change colour from light to dark when they are quite moist. The weight changes too and you can easily tell a dry from a wet bag. To rejuvenate you simply put them in the oven on the lowest settings for a few hours to burn off the moisture and they’re ready to be used again.

All of these methods simply help you manage condensation, it’s a thing that is around constantly, but more or less on sunny, windy and rainy days: you can’t ever beat condensation completely. I know of one motorhome owner who blocked all of his vents and sealed every nook and cranny he could find on the basis that it would keep cold air out thus avoiding condensation. Of course what happened was the lack of ventilation made things worse because the water could not evaporate so he got much worse damp than he would otherwise have suffered. 

A 12 volt dehumidifier
A 12 volt dehumidifier

On cold days in winter I run my fire at it’s lowest setting pretty much all night. Part of the reason is to prevent pipes freezing and to keep ambient temperature reasonable. But because the fire is lit and producing heat which causes condensation when it meets cold surfaces, it’s best to keep a vent or window open. Even during freezing days I find with the fire turned up higher to keep me warm, it’s best to keep a window open for ventilation. If there is any movement of air like from a light breeze, this actually helps the warm air in the van move around, which helps reduce condensation but even without a breeze the meeting of warm and cold air creates it’s own movement. 

But if warm air carries moisture surely you’re making moisture by having the fire on? No, by having warm air you’re heating the cold surfaces to some degree, so that less water condenses. There are some who claim that they never suffer condensation and that you need extra insulation, or you have a leak, or some other excuse. It’s simply not true. Every motorhome gets it and as said at the beginning, you can’t change the laws of physics, Jim.

Most motorhome owners have a habitation service carried out annually and they always check for damp so take heed of any warning of dampness and deal with it quickly because the effects of damp can be unimaginably expensive. 
Do some checks yourself for cold spots in your van, these are likely to be the places that condensation occurs; little used cupboards, underbed storage, overcab bunks. When you find cold spots check them for damp when conditions are ripe, such as when waking on cold mornings in winter, late evenings in winter when the heating has been on for some time. 
If cupboards are packed tightly this restricts airflow, move some things out so that air can move. 
On warm and windy days open your windows. It’s good for window rubbers to have windows opened regularly anyway and gives you a chance to clean the windows thoroughly and clean the rubbers. Oiling the windows every couple of years is also advisable to help keep the rubber in good condition. 
Choose a method to combat damp, but check regularly and if it’s not working try a different method. 

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