Condensation created by propane heaters.

[D. Jonas Jr.]

We just purchased a 1979 34V. Doing research about wood stoves and other heat sources inside the camper, I have read a couple references to "interior condensation" occuring during long use of the propane furnace. What is this issue? What happens?

[Razorback]

Welcome to the forum!

I have not had a condensation problem with the regular furnace, but see it with the Wave 8 catalytic heater that we use frequently. Normal result of an unvented gas heater.

[KYAvion]

Any of those "vent free" blue flame or infrared heaters will produce a lot of moisture. These are different than the catalytic heater mentioned by Razorback.

I do a lot of camping in cold temps and I do experience some condensation on the windows, but it's simply a matter of warm air colliding with cold. That said, ventilation is important when showering, cooking on the stove, etc. just as it would be at home.

I did talk to some people in a newer Airstream once who were experiencing condesation on the walls. I suspect in their case the moisture was likely due to the low R-value of the fiberglass in between their trailer skins, which is something an Avion doesn't have a problem with due to the higher R-value foam.

Now I did experience some mild frozen condensation along the lower wall behind my kitchen cabinets once. However, it was literally the coldest weekend of the year (single digit temps), and I suspect the source was likely air leakage from the open cavity to the fresh water tank.

[silverloaf]

We just purchased a 1979 34V. Doing research about wood stoves and other heat sources inside the camper, I have read a couple references to "interior condensation" occuring during long use of the propane furnace. What is this issue? What happens?

Condensation forms whenever an inside surface reaches dew point. Dew point is the air temperature where the air is unable to hold any more water molecules and they fall out of suspension.

The aluminum wall framing acts as a "thermal bridge" between the outside and inside wall surfaces. Metal is the perfect conductor. Under the right conditions, the outside temperature overwhelms the heat source. This causes the air to reach dew point and moisture to transfer to the surface.

Fortunately, the effects of thermal bridging are minimized in an Avion due to the closed-cell spray foam insulation. Its R-value and density help restrict the thermal bridging to mainly the contact points of the framing (conduction).

Fiberglass insulation is too porous to keep the wall cavities warm. the entire wall becomes the thermal bridge (conduction and convection); hence, the Airstream problem.

I used to do building performance diagnostics, using a lot of specialized equipment like an infrared thermal imaging camera. Houses and buildings are no different than trailers when it comes to the causes of condensation.

[slowmover]

It will depend on integrity of structure (door & window seals), number of people, pets and how often door is opened.

1). A de-humidifier is a required tool, IMO. Big one. Floor model that rolls.

2). Find the HEHR catalog (Pellandent) and do what the cheapskate original owner didn’t do: order proper interior storm windows. They’re useful year-round.

3). Look into CHEAP HEAT electric furnace addition. (You can use roof AC to circulate air with FAN ONLY switch position for any heat source).

4). The real problem is plumbing. That’s an extensive prep subject.

5). Custom skirts is where I’d start.

.

[KYAvion]

Slowmover—great idea about ordering storm windows. Would those seal differently than homemade ones fabricated out of plexi or lexan that fasten to the inside wall?

[Salty]

My Avion came with what was referred to as winter package. All of the windows have what I could best describe as an interior storm window. The glass on either side of the windows that open have an interior piece of glass that has a rubber seal around it and is held in place on three sides by clips and the fourth by a piece of plastic channel. The glass itself bears the Hehr logo.

As for a dehumidifier, in Texas, I think it's mandatory equipment. At least anywhere east of San Antonio.

[Razorback]

My Avion came with what was referred to as winter package. All of the windows have what I could best describe as an interior storm window. The glass on either side of the windows that open have an interior piece of glass that has a rubber seal around it and is held in place on three sides by clips and the fourth by a piece of plastic channel. The glass itself bears the Hehr logo.

As for a dehumidifier, in Texas, I think it's mandatory equipment. At least anywhere east of San Antonio.

I have never seen the Hehr storm windows, but have always heard about them. Can you provide some pictures?

[KYAvion]

Thanks Salty. About how deep of an insulating air gap is created by the rubber seals? Nothing covers the windows that open?

In my case I don’t open my windows at all in the winter, so I may be best off creating a single piece to cover the entire window. Each piece could fasten to the walls with clips. I imagine a simple gasket would help to make these relatively air tight.

[Salty]

The insulating air gap is only the depth of the window. The glass and seal fit up against the window Fram on the inside.
@razorback
I'll try to get some pics.