Roof fan speed cold weather?


For context; I’m full time in a 2016 transit with plastic bottle insulation behind thin plywood (roof and walls). Its just me in the van, I cook once a day and make a coffee in the morning…both using propane/butane mix.

Ventilation is via windows open sufficiently to match the surface area of the max fan located over platform bed at rear of van.

Heat is dry from a planar 4kw diesal heater towards front of van that I’ve run ducting from to distribute heat into living area between boarded front of bed and cab/living area bulkhead (door cut in so air can flow), under bed and blowing on me on top of bed.

I think I understand the principles of condensation and that I need adequate and effective ventilation to manage it while adding dry heat to stay comfortable/override the associated cold that ventilation brings with it.

I have been running my fan on 20% exhaust speed for the last few weeks and while I’ve been able to mostly avoid internal condensation (inc all glass), I have noticed persistent condensation on the metal rood behind the ceiling insulation (I can get my hand behind an unfinished section and took a few panels down to investigate last week). We have been between -3 and +9 deg Celsius for the duration of my time living in the van.

My guess this is due to either insufficient or ineffective ventilation.

One theory I have is that the fan speed is inadequate to remove the volume of moisture I’m producing.

The other theory I have is that it’s due to ineffective air flow between insulation and ceiling boarding.

I’m leaning to the later as the un insulted metal over the cab is staying dry but thought I’d see what others do fan speed wise in winter incase I’ve running it to slow?

Long post so thanks for reading if you did.


This is very common, but often hidden problem. Insulation doesn’t stop condensation, but it does often hide it and/or trap it.

The vehicle manufacturers solve this problem in one of two ways, either the outside skin gets ventilation, or the moisture is wicked away from the skin to the interior where it can be evaporated out.

With my van, I replaced all the stock interior panels to restore the air flow behind them. You can’t see it working, hear it working, or feel it working, but it’s silently protecting my van’s body from collecting and trapping condensation.

Even as extreme weather camper (it’s -20°f outside right now), I’m warm and comfy inside my uninsulated camper van, and it costs me under $20/mo to cover my heating & cooking, even in these frigid temps. I don’t even insulate or cover my windows or separate my cab & cabin. For me, proper heating & cooling methods have totally eliminated the need for added insulation.


"Always avoid complicated solutions to solve simple problems." ~ OffGrid

1 Like

Thankyou for the feedback.

I’m starting to understand your perspective as I continue to full time.

For me, I’ve come to realise well, maybe suspect, that the key change I can make to improve cold weather comfort is to have my fresh air source pre heated by my dry heater. This will mean I can have the windows closed (extract fan still going). To achieve this I am making enquiries wrt moving the diesal heater to outside the vehicle so fresh air is being warmed and pumped into the vehicle.

Interesting points on insulation…how do you find hot weather with no insulation?

My thinking at the moment is to replace the plastic bottle quilt that is closely trapping moisture with some closed cell foam.

I’ve never heard of plastic bottle insulation before. We keep our propane heater on low all night with our fan on low and we never have condensation issues. We rarely see temps below 30f though. We used to get condensation before we had a roof and insulation.

It sounds like you might have an air flow problem to me. As in the warm air is coming into contact with the cold metal too easily.


I use an energy efficient 12v swamp cooler, the indirect type, and even in hot & humid areas, it keeps my interior temperature comfortable, and the humidity levels down.

I don’t have any added insulation or condensation problems. My choice was good heating/cooling options instead. I almost never close my windows, and just have enough heating/cooling to compensate for it.

Right now it’s 12°f outside with 80% humidity. Inside it’s 75°f with 29% humidity, with both front windows cracked about an inch. I don’t have, want, or need roof vents because I have opening windows all the way around. I do believe fresh air is important.

With open vents or windows, which is pretty much required, I think it renders insulation pretty much useless anyway…


"Hope for the best, but prepare for the worst." ~ Murphy