Exhale into a drinking glass or small jar and you’ll see condensation in it. Now imagine how much moisture one person exhales every hour they spend in an RV. If you combine perspiration and exhalation, the amount of moisture in your RV increases by about 1/10th of a gallon or roughly half a liter every 12 hours, for every person in it. That might not sound like much to some people, but if you put that amount in a kettle or humidifier inside your RV – for a third of every day – you’d definitely notice.
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In hot weather, you won’t notice the moisture as much since warm air – inside your RV – can hold more moisture, preventing condensation on surfaces. Also, if you have an RV air conditioner, the cooler, drier air it provides will lower the moisture content in your motorhome, trailer, or camper.
Moisture becomes a problem when things get cooler. If you remember your middle school science classes, there was probably one where you put ice water in a glass, and then noted the condensation that collected on it. In the case of an RV, the “ice water” is often colder outdoor temperatures (at night or all day long). On the glass, the condensation collects on the warm side. In your RV, the warm side is most often the interior.
The above means that anytime the inside of the RV is warmer than the outside, you can generate condensation – on windows, walls, underneath flooring, behind wall coverings, and so on. It’s also what creates that cool-ish, damp feeling when you wake up after a cold night.
Another source of moisture in your RV is water leakage from the outside – rain or wash water through gaps in the seals or penetration points. This can let in large amounts of water and moisture, both where you can see it, and where you can’t… until it’s too late.
Controlling moisture in an RV requires some simple, basic, but extremely important things.
First of all, you probably have screened windows and roof vents in your RV. Use them. When you can, use the windows and roof vents together to create air flow. The hot air near the ceiling will naturally exit through the roof vent and the slight negative pressure will draw air in through the RV windows. If there’s a breeze, it can really help to have a window open on the upwind and downwind side of the RV.
If it’s hot enough to use your air conditioner, make sure the condensation is draining on the outside of the RV – usually seen as water running off the roof. Get up on the roof every now and then to check. If the RV’s air conditioner condensation is making its way into the roof or walls, that’s a lot of water over time.
If your RV has a shower, make sure you run the bathroom’s exhaust fan during, and well after, your shower. Similarly, if you’re cooking, use whatever exhaust fan is closest to the cooking area.
If you choose to be extra careful, you can invest in a dehumidifier sized for your RV.
Exterior leaks require careful inspections of the existing seals, sealants, and penetration points (places where wires, tubes, windows, etc. go through the roof, or walls (or even the floor. It’s surprising how much water can be forced through a bottom opening when driving through the rain.)).
Also, do a beginning-of-season and end-of-season inspection for evidence of leaks on the inside of your RV. Cover all the places you wouldn’t see on a regular basis. The back of cabinets, behind appliances, etc.
All the best, and here’s hoping your R-V is always D-R-Y.