What's an acceptable level?

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RVRAC

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Question for those of you with more experience.  What humidity percentage is an acceptable level inside a FW or motorhome? Winter is coming an sometimes windows get damp or wet inside, I heard is because humidity.  This is the reason I'm asking the question.
 

scottydl

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I'm not sure there is an "acceptable" level... a lot depends on your region, and the severity of the winter weather in your area.  Some people here have mentioned using Damp-Rid in the off season to control humidity if it becomes a problem.  In the Midwest the winter months are always pretty dry, so I have never had a big problem with windows fogging.
 

grashley

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This is a complex question.  Short answer - it changes.

Dew Point is the temperature at which atmospheric moisture will condense on a surface.  This is NOT impacted by air temperature.
Relative Humidity  is the ratio of current atmospheric moisture level to dew point AT A GIVEN (current air) TEMPERATURE.
On a nice, calm day, DP will change very little.  RH will increase significantly at night (cool) and decrease significantly during the heat of the day.

In the winter with cold windows, an indoor relative humidity of 40% will often be above the window dew point (condensation occurs).  In the summer, even 80 or 90% RH will not condense because it is hot outside.

The window condensation test is a good measure of when humidity is too high.  Normally, windows are the least insulated, therefore coldest surface in your RV.  If water does not condense on windows, it is unlikely condensing anywhere else.
If the windows are collecting condensation, which may then run down into the walls and cause damage, other surfaces may be doing the same thing.  Humidity is too high.

Dry air is sometimes hard on the throat and lungs.  It dries them out.

So, there is no simple answer.  I hope this helps.
 

OLDRACER

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For me, acceptable is when windows etc. are not moist. I open the lowest window I have just a bit, and a vent on the other end just a bit, that slow flow does the trick.

If not, moisture makes mold, yecch!
 

scottydl

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OLDRACER said:
For me, acceptable is when windows etc. are not moist. I open the lowest window I have just a bit, and a vent on the other end just a bit, that slow flow does the trick.

I forgot about this trick, and originally thought that seemed strange (leaving a window open in the dead of winter)... but it does reduce moisture build-up, and the unheated/stored RV doesn't know any different with a window open.  I'm not sure I would leave anything open if the rig is in a remote storage lot somewhere, but I'm lucky that I keep mine in my side driveway about 15 feet from my house. :)
 

donn

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I find under 45% RH to be comfortable.  We leave our RV parked during the winter.  Before running a dehumidifier first couple of trips was like sleeping in a swimming pool.  Bedding was always damp.  Now running my dehumidifier 24/7 first trip is nice and comfortable.  Living full time can create a lot of moisture.  Get a couple of smaller debimidifiers and run them all the time.  You wont regret it.
 

OLDRACER

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Opening lower/upper for airflow works if you are living in it too. Really noticeable in something small, like a truck camper, where windows and metal parts would have condensation without the flow, but same with big rig.

We water based critters give off a lot of humidity, it has to go somewhere. Since we dry camp a lot, dehumidifiers will not work for us.
 

rebelsun

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I have roof vent covers on my RV, so I leave them open to get some air inside the vehicle.  I also use damp rid, which seems to help, when the container is full of water, just dump it out, and add more damp rid. 
I'm sure a dehumidifier would work well, they always worked in my damp basements up north, but unless you attach a drain hose to the water catch tank, you have to go out to the RV daily, and empty the water bucket, or the machine will shut down when the tank is full.
 

Gary RV_Wizard

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Acceptable to you for comfort, or acceptable to the RV for minimal moisture problems? In any case, there will be no fixed answer. One is very personal, and the other is a matter of degree.

For the RV, something in the 20%-45% relative humidity range is probably ideal, but whether more (or less) might be potentially harmful depends a lot of the materials and workmanship in the construction. I've seen wallpaper peeling in new RVs on the dealer lot in Florida in a few inexpensive brands, and I've seen others that had no issues at all in 80% humidity.

Water condensing on the windows to the point where it runs down is not a good thing. Just a dusting of fog on the inside is probably no big deal, but it is a sign that some ventilation would be advisable.
 

scottydl

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RVRAC said:
Question for those of you with more experience.  What humidity percentage is an acceptable level inside a FW or motorhome? Winter is coming an sometimes windows get damp or wet inside, I heard is because humidity.  This is the reason I'm asking the question.

Will you be occupying the RV during winter months, or will it be empty in storage?  That makes a big difference.  I never asked, but have seen responses in both directions.
 
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