Airstream has used several venting systems over the years. The first and best one was when the air came in through a screened opening in the belly pan and up through an opening in the sub floor, and out through a vent in the roof. Access to the refrigerator back was through a door in the outside of the trailer. Gravity did all the work to remove the refrigerator heat and it was an excellent system.
The next variation eliminated the hole in the belly pan and sub floor, and brought the cooling air through the access door to the back of the refrigerator by cutting vent holes in the door and screening it. Air still went out the roof vent. It worked pretty well.
The latest twist is to put two outside access doors on the refrigerator compartment, both with holes, to eliminate the roof vent. The air chimney is only about 3' high max and so does not work nearly as well as an 8' high stack of the old system. So, to augment the air flow, they put a fan at the top access door to move air through the system.
The problem is that the fan they use is loud and takes power all the time to run it. For us boondockers the noise is unwelcome in quiet locations and the constant battery use is not good.
The partial solution has been to replace the original fan with ones which make less noise and use less power. I have gone one step farther by directly venting the boiler heat and propane gasses from the top of the refrigerator directly to the outside so they don't add to the heat which must be eliminated by the fan in the compartment.
BTW, the earliest Airstreams with propane refrigerators used a 2" vent pipe for the propane heat and gasses from the boiler and that pipe went up through the roof like a plumbing vent. The refrigerator coil heat went directly into the rig, via a screened vent in the countertop. I had a 1960
which was set up that way from the factory.
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