Most people think about their RV's roof vent at the campground. We think about it in November, when the rig heads to a storage lot or side yard for months. After 45 years on roofs, we've learned that a closed-up RV acts a lot like a closed-up attic, shed or shipping container. Same physics, smaller box, wheels underneath.
Why RVs sweat
Condensation is water vapor turning back into liquid when it touches a cold surface. Winnebago puts the source simply: "Just breathing in your RV creates water vapor!" Cooking, showers, wet towels and damp gear add more.
Then the building itself makes it worse. Winnebago's service bulletin, Service Tips from the Pros, explains that modern coaches can be "virtually airtight when closed up," while metal in the sidewalls and around openings carries cold inside where moisture condenses.
That's the same "beer can effect" we see in metal sheds and containers. Warm, moist air meets a cold metal surface, and it beads up like a cold can on a summer day. We covered the container version in Container Rain.
What the RV makers say
RV makers agree on the basic fix, and it's the one we preach for attics: move the moist air out.
- Winnebago: "The most effective way to deal with condensation is to ventilate your coach." And: "Removing this moist air is the best way to prevent this condensation from forming."
- Jayco: its Terrain owner's manual says to "Crack open windows and roof vents to allow warm moist air to escape."
- Forest River: its motorized owner's manual says, "It is especially important to air out your RV when storing, or if you do not anticipate using it for an extended period of time."
Forest River also gives a target: "Keep indoor humidity low, below 60%, ideally between 30 and 50%, relative humidity." A cheap humidity meter tells you where you stand.
Why it matters for your wallet
Moisture you can see on a window is a warning. Moisture you can't see, inside cabinets, behind cushions or in the walls, is where the money goes. Winnebago's bulletin warns that in severe cases owners "may develop dry rot or structural damage to the wooden components in the coach," and that this damage "is usually quite expensive to repair."
Read your warranty, too. Jayco's manual notes that "damage caused by condensation is not warrantable." Forest River's manual calls mold and mildew damage a maintenance issue. In other words, it's on the owner.
Getting a stored RV ready
Before your RV sits:
- Dry it out first. Empty and dry the fridge and freezer, wipe down the shower, and check under sinks for drips.
- Open cabinets, closets and drawers. Winnebago notes that "Opening a window or vent can go a long way toward reducing RV condensation," and suggests cracking closet and cabinet doors so hidden walls get air.
- Crack a roof vent only if it's covered. A vent lid left open with no rain cover is a leak waiting to happen. Follow your RV maker's manual and your storage lot's rules.
- Keep air moving. Forest River suggests recirculating air with vent fans or small fans. It also warns, "Do not use a ceramic heater, as it provides no air movement and will not aid in reducing condensation in the RV."
- Check on it. Look for fogged windows, a musty smell or damp spots. Those mean the moisture needs somewhere to go.
Arizona storage is its own animal
Here in the desert, the bigger enemy most of the year is heat. An RV parked in the sun with every vent shut bakes from the roof down. Then winter nights get cold enough that any moisture left inside can show up on windows and metal. Heat out high in summer, moisture out in winter. It's the same two-season problem attics have.
Where a Solar Blaster fan fits, and where it doesn't
To be clear, we don't make an RV roof vent. The vents and fans on your RV's roof come from the RV industry, and your RV maker's manual should guide what goes there.
Where we fit is the building you store it in. An enclosed RV garage, a pole barn or a metal storage building gets the same heat and condensation we fight in garages and sheds. Those buildings follow our usual rule: intake low, exhaust high, balanced. See How to Ventilate a Hot Garage for the basics.
Bigger is not better. A high-CFM fan with weak intake just pulls air from wherever it can, through gaps and cracks. Size the fan to the space and give it intake. Our product pages use a 10'x10'x10' space, or 1,000 cubic feet, as the example:
- The Solar Mega RoofBlaster moves 96 cfm, about one air exchange every 10.4 minutes with proper intake ventilation.
- The Solar RoofBlaster moves 35.2 cfm, about every 28.4 minutes with proper intake ventilation.
- For metal-roofed buildings with a ridge vent, the Solar Metal RidgeBlaster is listed at the same 28.4 minutes.
An RV building is far bigger than 1,000 cubic feet, so it may need more than one fan plus plenty of low intake. We explain why in Why Solar Blaster Bets on Balance, Not Brute Force.
Being honest about the limits
- Ventilation helps manage moisture. It doesn't fix leaks. A cracked roof seam, a bad window seal or a plumbing drip needs repair, not air.
- In humid or very cold storage, airflow alone may not be enough. The RV makers above also mention dehumidifiers for those conditions.
- A fan on the storage building doesn't ventilate inside a closed RV. You still need to dry out and open up the RV itself.
- We won't tell you a fan kills mold or fixes every moisture problem. It doesn't. Clean up existing mold properly and fix the water source.
- Your RV's manual, your warranty and your storage facility's rules come first.
The bottom line
A stored RV is a small, tight building that holds onto moisture. Dry it out, open it up, keep air moving and check on it. If it lives in a garage or storage building, ventilate that building the right way: balanced intake low, exhaust high, and a right-sized fan instead of the biggest one.
As Daniel Rheaume of Solar Blaster puts it, "Our products move air, which is a natural cleanser. Clothesline fresh."
Questions about your attic? Call us at (480) 747-7097 or email sales@solarblasterfans.com.
