Condensation on upper inside walls ral cold morn

The propensity for condensation to form on the interior surfaces of an rv is a function of 2 factors:
1- The interior relative humidity
2- The temperature of the interior surface
The greater the rh inside the rv, the greater the propensity for condensation to form.
The lower the surface temp inside the rv, the greater the propensity for condensation to form.
Adding heat to the inside of the rv will tend to reduce the formation of condensation by increasing the surface temp inside the rv.
Adding heat to the inside of the rv will tend to reduce the formation of condensation by decreasing the rh.
If outdoor temp is 50 degrees F with rh of 100%, (ie it's raining) and you bring that outdoor air inside the rv where the temp is 70 degrees, the rh will decrease to 49%.
The greater the difference between indoor and outdoor temps, the more dramatic the decrease in rh.

luberhill wrote:
So last night we had a cold rainy night, got down to 40 and I kept the inside around 65 but then turned it to 70 when we woke
I notice if you put you fingers on what the call “ wallboard” up close to the ceiling it feels cold and damp .
Assume it’s because the outside walls are so cold and it’s hot inside ??

Only way to prevent condensation is to make an RV insulated as an S&B house..
One reason I built my own and put rigid board insulation everywhere walls,floor,ceiling even door..have double pane windows too..
Use Espar diesel heater..its dry even at -20..

The condensation is generated by running your propane appliances. I usually open a roof vent about 2 inches to let condensation escape. Otherwise it will collect on the walls and windows.

Water released by a human body is called "sensible" and "insensible" in the medical/scientific world. Sensible is what's released by a body in the form of pee & poo and can be easily measured. Insensible" is moisture released by the body from perspiration and respiration and can't be easily measured. For the average adult in a "normal" temp. and humidity environment, the body releases around 40 ounces per 24 hours (5 cups per day) into the surrounding air from perspiration and respiration.

A more accurate figure of the amount of moisture released into the air by a human (or pet) isn't a question. There's enough moisture released from an average human over 24 hours regardless, that it MUST be removed in cold weather. Then on top of that cooking & showering releases even more moisture into the air.

You have to resist the temptation the seal up every crack and opening to retain heat. The moisture has to be removed. Failure to do so can result in mold, rot & delamination. For more than the odd cold weather weekend outing, a dehumidifier is the best solution as mentioned numerous times. Note also that the warmer air is, the more moisture it will hold so don't think cranking up the thermostat will help. A hygrometer would be a help so you can keep tabs on the RH and they don't cost much.

For occasional weekend trips, running a roof fan and cracking open a a couple of windows can work. We just spent the weekend camping and it was raining hard part of the time. We have one of our two Maxxair fans running non-stop on low and the humidity was hovering around 50% which is fine (2 adults + dog) and no signs of condendsation.

I read of one case where a person wintering in the Seattle area that had water raining down on him from his ceiling. Simply due to a failure to remove moisture from the inside air.

Yup, small box, inside moisture sources (humidity, human breath, cooking, shower steam etc. )
Yes leave a roof vent open a bit for air to circulate better and humidity to escape.
No you don't have to open up the camper. That defeats the purpose of heating it.

mchero wrote:
Great information!
We have been full timing for last 3 years. We squeegee the shower walls after showering.
We also run ventless propane heater and also keep window/vent cracked.
Looking at de-humidifiers BUT want a low amp draw unit. How many amps these smaller units draw?

My discontinued 15pt comes on at bout 4 then drops back to 2 amps. Other 15pt'ers I've seen draw from 300-600w depending on the setting.

my small, D/H draws 6 amps and works good in my 27ft. T/T.
Jay D.

mchero wrote:
Great information!
We have been full timing for last 3 years. We squeegee the shower walls after showering.
We also run ventless propane heater and also keep window/vent cracked.
Looking at de-humidifiers BUT want a low amp draw unit. How many amps these smaller units draw?

a ventless propane heater will dump about 3.5 quarts of water into the camper air for every gallon of propane burned. works against keeping the trailer dry in wet climates. works nice in very dry places to humidify. Same with your stove/oven. Furnace and HWH vent the exhaust outside so no water inside.

smaller units draw around 2-3 amps @ 120V figure 200-300 running watts.

Great information!
We have been full timing for last 3 years. We squeegee the shower walls after showering.
We also run ventless propane heater and also keep window/vent cracked.
Looking at de-humidifiers BUT want a low amp draw unit. How many amps these smaller units draw?

Boy, I really hate to admit ignorance, but my 10 year old Carrier AC units have a "Dry" setting on the controller. I guess I should look up what that does....