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WenWes · 10-10-2013, 09:00 AM

Having moisture on inside window panes overnite when using furnace. SUGGESTIONS????

TXiceman · 10-10-2013, 09:15 AM

The furnace is not the problem as it is vented to the outside.

You problem is too much moisture within the RV. The dewpoint of the air is higher than the temperature of the glass surface or frames. The excess moisture is condensed on the cold surface.

During cooler weather you need to keep the moisture down. Moisture sources are you breathing, moisture from the skin, cooking and showering. OK, you have to breathe, so you will need to keep one roof vent open slightly. Warm moisture air will rise and exit.

Next, when you shower, open the roof vent in the bath area about 3" or 4". As soon as you finish showering, turn on the vent fan to pull the moist air out. Use a squeegee to wipe down the shower walls and push the water to the drain.

When cooking, open a vent and get the moisture out.

I know you want to keep the RV closed up tight to conserve the heat, but you can't get rid of the moisture unless you vent. An alternate is to run a dehumidifier and then empty the collection tank fairly often.

One common misconception is that the propane furnace makes the moisture in the RV. That is totally wrong. The combustion process does produce water vapor, but the combustion is totally outside of the heated area of the RV. The furnace fan blows air across the heat exchanger and heats the air. The flame is on the other side of the heat exchanger and the air is picked up outside and vented outside.

Ken

chief02 · 10-10-2013, 09:18 AM

Ventlation is all u can do. Crack open a roof vent and window or get a dehumidifier. I know opening a window and vent with the heat on seems counter productive but it works. Propane heat generates tons of moisture when pulling moist cool air from the outside into the heat exchanger plenty of it enters the trailer. TX is correct about dew point differentials but I guess we disaggree about moisture from the furnace.

TXiceman · 10-10-2013, 09:50 AM

Chief, how does the propane combustion get the moisture into the RV. Been in the refrigeration and A/C business since 1970, and I have yet to see what you describe happen. The RV furnace works just like a residential furnace.

As far as the air with in the RV is concerned, it is passing across a hot surface, it does not matter whether it is heated by propane, natural gas or a hot electric heater.

The old open flame gas heaters like the Dearborn heaters did add moisture and carbon monoxide to the heated space.

The RV furnace has an external air inlet to the combustion heat exchanger and is force drafted with a fan. The air inside the RV is forced by a fan over the OTHER side of the heat exchanger is heated in a sensible heat process. By heating the air, the moisture content is not changed one bit. You still have the same grains of moisture per pound of air.

Air Psychrometrics
Plenty of reading on the psychometric process at this site.

mel s · 10-10-2013, 10:23 AM

Quote:

Originally Posted by chief02

Propane heat generates tons of moisture when pulling moist cool air from the outside into the heat exchanger plenty of it enters the trailer.

chief02
I agree with TXiceman.
All moisture generated by the combustion of propane in a properly sealed RV propane furnace exits the RV with the exhaust.
If any combustion moisture is getting into the coach it is likely that carbon monoxide is as well!
Mel
'96 Safari

BFlinn181 · 10-10-2013, 01:14 PM

Moisture build up is always a problem in RVs. Open a vent or a window or stop breathing, cooking or showering are other options. I notice windows hidden behind shades or curtains are more likely 'fogged' than those left uncovered. During cold nights I might keep windows closed, but upon rising I crack open the roof vent and a window or two. I pull the curtains back from the windshield early to give it time to dry off before we drive off. Cooking or showering is always offset by an open roof vent or hood vent.

I agree with TXiceman, LP furnace doesn't contribute to moisture since it's combustion is kept separate from interior air.

2Boilermkrs · 10-14-2013, 06:12 PM

I've read all the threads in this topic and gather that air circulation and getting a dehumidifier are my only two options for reducing condensation. My husband and I just bought our very first Motorhome (2007 Winnebago Aspect 26a) this past August. We are living in it full time now so when I see water building up only around the bottom of the walls in the bathroom and around the toilet I'm a little uneasy. I don't believe there is a leak anywhere because we had a few warm days and during that time (plus back in August and Sept) there was no water, and as the temperature lowers, more and more accumulates. There is no condensation gathering around the windows...just an FYI. I've also looked to see if I can put anymore insulation anywhere to help but I have no access to the storage tanks...which is my guess as to what is causing it. I should also mention that where the pump and wireing and fresh water tank is being stored (under the bed) there is water between the linoleum and the plastic vapor barrier that all that stuff sits on. Any suggestions...similar situations?

BFlinn181 · 10-14-2013, 06:52 PM

Put a small fan or electric heater on floor blowing towards bathroom walls. It sounds like insulation is inadequate in walls in those areas, but it will be very difficult to improve insulation. I see your RV has double pane windows, that's why they stay dry. Are your wet bay tanks heated? This is often done by a duct from the heater blowing in that compartment. Water tank under bed should be almost inside coach temperature. Again, a small fan blowing on linoleum floor under bed might help dry it out. Continued moisture in those areas (Bath wall and under bed) will cause mold and rot issues if you can't insulate or dry it out with fans. Keep a roof vent open a bit to help get rid of excess moisture so it doesn't condense on the cold spots.