Condensation/Temp Control

All in all, I think I'd keep the curtains closed and go with the rolled up towel on the dashboard.

Better yet, fire it up and head south! :B

A third solution. Insulate the bottom of the front window for about six inches with tight fitting foam, on the outside of the RV.

This allows the bottom of the glass inside to be above the dew point temperature. The water runs down, hits the warm glass and "evaporates" back into the air inside the RV.

from the Department of Redundancy Department.

way2roll wrote:

wallynm wrote:
So please explain why the RV furnace has a hot exhaust vent on the outside. Some RV furnaces also has an antisale switch to keep the furnace from coming on if an obstruction does not allow the combustion gasses from exhausting.

way2roll wrote:

msturtz wrote:

way2roll wrote:

msturtz wrote:

way2roll wrote:
I had a similar issue once in our first class A. A literal waterfall was running down my windshield. A by-product of burning LP is water. So if you have an LP furnace you are not only creating condensation by differing temperatures, you are pumping H20 into the air via your furnace. Showers and cooking exacerbate the issue. The best way I have found to combat this is to open your roof vents and run the vent fans. I know it seems like you will be pulling your heated air out of the coach - and you are - but you will also be pulling out the moisture. A dehumidifier is always helpful as well.

You are technically correct burning propane does create a lot of water vapor, however per code RV furnaces must have an external air intake and external exhaust for combustion. All you get inside the coach is hot dry air. This is not true with small portable heaters. So no running your RV furnace will not put water vapor into the air.

A lot of folks disagree;

http://www.irv2.com/forums/f93/engineering-help-water-from-propane-104216.html

The confusion is coming from the use of ventless heaters. Installed propane heaters are prohibited from venting exhaust gas (including water vapor) inside the coach.

I am not going to get into a pi$$ing match with you over it. If you tell me that RV furnaces are designed to mitigate water vapor induction into the coach when it's well known that burning lp generates 1-2 gals of water per gal of LP - sorry but that's a hard sell. I tend to believe that your LP furnace - vented or not - pumps a good amount of water vapor into the RV. It's certainly not going through any sophisticated air scrubber as you can smell the additives in the LP when it burns. And if you can smell that, it's a good bet you are getting exhaust gasses - not just the heat. LP furnaces are not complicated and the vents are passive. Moving on.

Please explain how my humidity monitor would spike in my coach prepping for a trip in the winter running only the LP furnace and no one was in the coach. Not just condensation, the ambient humidity. Outside humidity 40%, coach almost 70%.

The humidity monitor may be incorrectly reading the humidity near the wall due to the lower ambient temperature, there is also an effect where building materials, clothes, and other porous materials will give off stored humidity as the humidity in the room drops. There is another possibility that could be that your furnace is defective and has a leaking heat exchanger which would be extremely important to correct immediately due to the issue of carbon monoxide poisoning. A properly designed, functioning and installed furnace cannot leak ANY exhaust gas into a coach.

way2roll wrote:

msturtz wrote:

way2roll wrote:

msturtz wrote:

way2roll wrote:
I had a similar issue once in our first class A. A literal waterfall was running down my windshield. A by-product of burning LP is water. So if you have an LP furnace you are not only creating condensation by differing temperatures, you are pumping H20 into the air via your furnace. Showers and cooking exacerbate the issue. The best way I have found to combat this is to open your roof vents and run the vent fans. I know it seems like you will be pulling your heated air out of the coach - and you are - but you will also be pulling out the moisture. A dehumidifier is always helpful as well.

You are technically correct burning propane does create a lot of water vapor, however per code RV furnaces must have an external air intake and external exhaust for combustion. All you get inside the coach is hot dry air. This is not true with small portable heaters. So no running your RV furnace will not put water vapor into the air.

A lot of folks disagree;

http://www.irv2.com/forums/f93/engineering-help-water-from-propane-104216.html

The confusion is coming from the use of ventless heaters. Installed propane heaters are prohibited from venting exhaust gas (including water vapor) inside the coach.

I am not going to get into a pi$$ing match with you over it. If you tell me that RV furnaces are designed to mitigate water vapor induction into the coach when it's well known that burning lp generates 1-2 gals of water per gal of LP - sorry but that's a hard sell. I tend to believe that your LP furnace - vented or not - pumps a good amount of water vapor into the RV. It's certainly not going through any sophisticated air scrubber as you can smell the additives in the LP when it burns. And if you can smell that, it's a good bet you are getting exhaust gasses - not just the heat. LP furnaces are not complicated and the vents are passive. Moving on.

This is not a matter of opinion or conjecture. It is a matter of code requirements. Per American National Standards Institute, Inc., and the institute's rules applicable to Low Voltage Systems in Conversion and Recreational Vehicles and Uniform Plan Approval for Recreational Vehicles, ANSI/RVIA 12V Low Voltage Systems, current edition, and ANSI/RVIA UPA-1 Standard on Uniform Plan Approval for Recreational Vehicles, current edition. These have been adopted by RVIA for any vehicle with the RVIA seal must comply and most states require state level approval for sale in that state. These codes REQUIRE the following:
All fuel-burning appliances, except ranges, ovens, illuminating appliances, … shall be designed and installed to provide for the complete separation of the combustion systems from the interior atmosphere of the Recreational [Vehicle]. Combustion air inlets and flue gas outlets shall be listed as components of the appliance. The required separation shall be permitted to be obtained by: 1) The installation of direct-vent systems (sealed combustion) appliances, or 2) The installation of appliances within enclosures so as to separate the appliance combustion system and venting system from the interior atmosphere. There shall not be any door, removable access panel or other opening into the enclosure from the inside of the Recreational [Vehicle] any opening for ducts, piping, wiring, etc. shall be sealed..”

Almost every state has adopted ANSI, NFPA, and or RVIA code requirements. All larger RV manufacturers install compliant LP heaters and every RV manufacturer that uses the RVIA seal must comply.
With a sealed combustion chamber or sealed compartment it is absolutely physically impossible to introduce water vapor into the inside of the coach. There is a heat exchanger (typically air to air) that allows the hot exhaust gas to heat the interior air. The reason for these regulations is to prevent death by carbon monoxide poisoning due to a malfunctioning heating appliance. The other reason is due to oxygen depletion in the interior air of a RV. In regular homes there is enough air leakage to allow combustion air to be drawn from inside the home without the risk of oxygen depletion however, in a small space such as a RV it is very possible to deplete enough oxygen to create health problems. This is why I am so opposed to the use of portable propane heaters inside of RVs they carry the risk of carbon monoxide poising and oxygen depletion with the added headache of massive quantities of water vapor which is a natural byproduct of burning propane. So, you are correct in the statement that burning propane does create a large quantity of water vapor it’s just vented outside.

All good points and make a lot of sense. Thanks for the explanation. Learn something new everyday.

The furnace is similar to the way the water heater works. The water heater has a heat tube where the combustion takes place. This heat tube loops around the water tank and then exits to the outside. At no time is the combustion flame or gases inside your coach, unless the heat tube has a hole in it.
The same thing happens with your furnace. There is a heat box that contains the combustion chamber with the flame that exhausts all gases to the exterior. The combustion flame also receives oxygen from the outside. The fan only blows interior air across the heated box and recycles that heated air throughout the coach. No combustion gases can get inside the coach unless there is a hole in the combustion chamber box, in which case your CO alarm would be blaring.
People, showers, and cooking all put moisture in to the air inside your coach. A resistance type heater will tend to minimize the effects of that moisture.
A simple fan is all you need to keep your windshield clear.

If a normal RV furnace is letting combustion gasses into the RV interior, the heat exchanger is shot and the furnace is unsafe to use and needs repair or replacement. Indeed, all other things being equal, using the furnace would decrease the relative humidity inside since the ratio of actual water vapor (unchanged) to the maximum noncondensing amount in the air (which goes up with temperature) is decreasing. The only RV propane appliance that would increase inside humidity (and sometimes quite noticeably) is the range. If you do have an unvented propane heater, that also would increase humidity inside.

The humidity monitor might be spiking because the sensor doesn't work very well at lower temperatures, or because something else is increasing the relative humidity (something damp that's drying out as the moisture that was formerly in or on it evaporates), or maybe even because the humidity sensor itself is cooler than the air that's being heated and so has some condensation forming on it. In the last case, the reading would correct itself over time.

wallynm wrote:
So please explain why the RV furnace has a hot exhaust vent on the outside. Some RV furnaces also has an antisale switch to keep the furnace from coming on if an obstruction does not allow the combustion gasses from exhausting.

way2roll wrote:

msturtz wrote:

way2roll wrote:

msturtz wrote:

way2roll wrote:
I had a similar issue once in our first class A. A literal waterfall was running down my windshield. A by-product of burning LP is water. So if you have an LP furnace you are not only creating condensation by differing temperatures, you are pumping H20 into the air via your furnace. Showers and cooking exacerbate the issue. The best way I have found to combat this is to open your roof vents and run the vent fans. I know it seems like you will be pulling your heated air out of the coach - and you are - but you will also be pulling out the moisture. A dehumidifier is always helpful as well.

You are technically correct burning propane does create a lot of water vapor, however per code RV furnaces must have an external air intake and external exhaust for combustion. All you get inside the coach is hot dry air. This is not true with small portable heaters. So no running your RV furnace will not put water vapor into the air.

A lot of folks disagree;

http://www.irv2.com/forums/f93/engineering-help-water-from-propane-104216.html

The confusion is coming from the use of ventless heaters. Installed propane heaters are prohibited from venting exhaust gas (including water vapor) inside the coach.

I am not going to get into a pi$$ing match with you over it. If you tell me that RV furnaces are designed to mitigate water vapor induction into the coach when it's well known that burning lp generates 1-2 gals of water per gal of LP - sorry but that's a hard sell. I tend to believe that your LP furnace - vented or not - pumps a good amount of water vapor into the RV. It's certainly not going through any sophisticated air scrubber as you can smell the additives in the LP when it burns. And if you can smell that, it's a good bet you are getting exhaust gasses - not just the heat. LP furnaces are not complicated and the vents are passive. Moving on.

Please explain how my humidity monitor would spike in my coach prepping for a trip in the winter running only the LP furnace and no one was in the coach. Not just condensation, the ambient humidity. Outside humidity 40%, coach almost 70%.

So please explain why the RV furnace has a hot exhaust vent on the outside. Some RV furnaces also has an antisale switch to keep the furnace from coming on if an obstruction does not allow the combustion gasses from exhausting.

way2roll wrote:

msturtz wrote:

way2roll wrote:

msturtz wrote:

way2roll wrote:
I had a similar issue once in our first class A. A literal waterfall was running down my windshield. A by-product of burning LP is water. So if you have an LP furnace you are not only creating condensation by differing temperatures, you are pumping H20 into the air via your furnace. Showers and cooking exacerbate the issue. The best way I have found to combat this is to open your roof vents and run the vent fans. I know it seems like you will be pulling your heated air out of the coach - and you are - but you will also be pulling out the moisture. A dehumidifier is always helpful as well.

You are technically correct burning propane does create a lot of water vapor, however per code RV furnaces must have an external air intake and external exhaust for combustion. All you get inside the coach is hot dry air. This is not true with small portable heaters. So no running your RV furnace will not put water vapor into the air.

A lot of folks disagree;

http://www.irv2.com/forums/f93/engineering-help-water-from-propane-104216.html

The confusion is coming from the use of ventless heaters. Installed propane heaters are prohibited from venting exhaust gas (including water vapor) inside the coach.

I am not going to get into a pi$$ing match with you over it. If you tell me that RV furnaces are designed to mitigate water vapor induction into the coach when it's well known that burning lp generates 1-2 gals of water per gal of LP - sorry but that's a hard sell. I tend to believe that your LP furnace - vented or not - pumps a good amount of water vapor into the RV. It's certainly not going through any sophisticated air scrubber as you can smell the additives in the LP when it burns. And if you can smell that, it's a good bet you are getting exhaust gasses - not just the heat. LP furnaces are not complicated and the vents are passive. Moving on.