This is a rough inside temperature test I did on our white ProMaster camper van conversion to try a few simple ways to keep it cooler.

The test covers:

The Test

My ProMaster camper van conversion is white, 136 wheel base, high roof…
It was parked with back facing south (back windows facing the sun).
It has about 1 inch of spray polyurethane.
My heat loss calculation says that this level of insulation plus the Reflectex shades cuts winter heat loss by 80%. It should have roughly the same effect on summer heat gain.


At 12:30 pm: (all closed up – no shades on windows)
Toutside = 75.2F, Tinside = 92.9F ( dif = 17.7F)

At the same time, the inside to outside temperature difference on our dark blue honda Pilot (parked right next to the PM and oriented the same way) was 45F more — so, the white color helps a lot for summer cooling.

Opened van windows, turned MaxxFan on full, put the Reflextex like windows shades in on all windows.

After 5 minutes:
Toutside = 75.2F, Tinside = 82.4F ( dif = 7.2F)

After half an hour:
Toutside = 75.0F, Tinside = 81.7F ( dif = 6.7F)

After nearly an hour:
Toutside = 77.7F, Tinside = 82.2F ( dif = 4.5F)

Turned the fan down to 30% setting, and checked the temp after half an hour:
Toutside = 79.0F, Tinside = 85.2F ( dif = 6.2F)

Inside Surface Temperature

Also took some readings on the ceiling, floor, and walls with an IR thermometer. Comfort is not only influenced by the air temp, but also by the temps of the surfaces of the room, as they radiate heat to you.
At start: Tceiling = 94F, Tfloor = 83F, Twall = 89F
After an hr with fan on: Tceiling = 88, Tfloor = 83, Twall = 87F

So, running the fan with windows open does three good things:
– Lowers the air temp.
– Lowers the temps of ceiling, wall, floor
– Creates some moving air, which feels cooler.


– If the vehicle is closed up, its going to get warm even if is white and insulated. The white helps reflect sun away and insulation slows influx of heat, but when the van is closed even that slower influx of heat is going to heat it up.

– Adding some ventilation and stopping the direct solar gain of the windows with the Reflectex shades helps a lot — lowers the outside to inside differential  from 18F down to 4.5F.

– It looks like one strategy for not coming back to a hot van would be to: 1) open the windows some, 2) turn the power roof fan on at low speed, and 3) put reflective shades in the windows — especially the ones facing the sun.

White vs Dark

During the same time period, our closed up Honda Pilot small SUV was sitting right next to the van — its dark blue. Temp inside varied from 117F to 125F. A 45F difference from outside to inside.
This is more than twice the difference the closed up van had at the same time — mostly the dark color I think.


Window Gain

For summer, direct solar gain through windows is a big swinger. If you have full sun shining through 20 sqft of window, this can be about (250 BTU/sqft*20sqft) = 5000 BTU/hr — this one thing is the total output of some of the small RV AC’s.

More Steps

It seems to me that something like 1 inch of polyiso rigid sheet, or about the same in spray polyurethane insulation is a pretty good level for winter or summer. 2 inches of polyiso (plus better insulating window shades) would cut your heat gain or loss in half again over 1 inch, but we are talking about going from an 80% reduction with 1 inch to a 90% reduction with 2 inches — there is a bit of a diminishing returns thing starting to set in.

If you can add a reflective layer near the van outer skin, I do think that would likely help with the radiation heat gain — especially if your van is not white. But, this reflective layer has to face an airspace to do anything.


August 2015