As some on here already now I am averse to cutting holes in my roof. My hope is to avoid having a roof vent. We expect to do minimal cooking inside our van and will have either CRL or Motion vented windows.
The jury is still out as far as I'm concerned. They are as much as a help as a hinderence in my opinion. It really depends on where you live, how you plan to use the van, etc. it's great to keep open in mild weather to allow the air to escape when you close the side door as well as keeping the van cooler and relatively moisture free but they can be noisy and another added expense. Cutting the hole in the roof and worrying about leaks is not something you should worry about. There have been next to zero posts on all the forums about leaky vents.
In the end, I do like having mind but is it necessary? NO! At least for my uses and climate. Would I do it again? I'm not sure!
Guess it all depends on where and how you will use your van. We often use ours in fairly warm weather where ventilation is required. When you leave your van parked it is very convenient to have continuous ventilation without worrying about rain (particularly if you have pets). In our van we have two Maxxairs with integral hoods mounted in the roof, one for intake and one for exhaust, using around 20 watts total on low speed. I guess you can do the same with awning windows but they are not easily obtained in the US. Without mechanical assist the actual cfm of airflow with windows can be miniscule. And protection against blowing rain can be difficult with the best of window arrangements. Just my take on the situation having owned three RV's in 16 years.
I concur, the vent is so handy when you want a safe and efficient ventilation system. We leave our Fantastic Vent open and on when the van sits in the yard to let air enter the awning windows and power exhaust through the roof. Go off for a hike or to tour a museum and return to a van that is being ventilated. It will be much better than those awning windows if there is no breeze. No amount of insulation will keep a van in the sun cool. The windows add heat. The power vent gets the van back near ambient temperature. Do It.
I put in a maxxair vent and it is great down here in south Florida. The thermostat kicks on when it gets over 95° (you can set the temp it kicks on) and it keeps the van at near ambient temperature in the blazing sun. I also installed window deflectors on the front windows so I can leave them cracked a few inches without worrying about rain.
I was apprehensive about cutting a 14x14 hole in my roof but it is worth it. Lots of butyl tape and no leaks.
My original post should have ready has anyone NOT had a roof vent.
I like the idea of the roof vent having a T'stat to automatically coming on and keeping the van cool. Some of our camping will be warmer weather and I am sure we will leave it places during the day where it will get warm.
One of the things I like about the CRL windows is that they have built in rain protection.
One the reasons we are resistance to a vent is our constant struggle with the roof vent in our horse trailer. No matter how much we caulk it it continues to leak.
You need to take off the roof vent on the trailer and properly clean the surface.
On the van you need to clean with methyl hydrate (alcohol ). Then use butyl tape.
Use extra layers in the valleys. Work great. Prep is important (clean surface).
Two years on my vent and no leaks yet. I have the max fan 7500. Can leave open in the rain even while driving.
If I leave the vent closed and go for a hike, it gets to hot inside. Glad I got it with no regrets.
Actually another questions - Where on the roof has everyone been installing these front, middle or back? I noticed on the BoB installation that the back end of the roof is not flat sheet metal so fillers were needed to complete the installation.
I installed mine in the back. I used 3 layers of butyl tape (or maybe putty tape...something like that) in the rib wells to fill in and make them level with the raised ribs. Then another strip of the tape all the way around. Seal with lap sealant. No leaks.
Wherever you want it. Front flat space is easiest, but Hein sells a filler piece so you can put it anywhere with similar ease. My understanding is that front is noisier. I made an insulating inner cover to silence my front-mounted MaxxAir.
Consider other things you may want on your upper real estate. For example, Hein makes adhesive pads that allow you to mount solar with just the one hole for wires. You could be unhappy were you to find that you want solar, but the fan is in the way. (Panels got mounted on mine this weekend after fighting the idea for two years, so I speak from experience as to how ideas evolve.)
As you noticed, I installed it at the rear. It went as far back as possible without having the cover overhang the rear edge of the roof.
My thoughts were that with the front windows open a bit the fan would do a better job of drawing air THROUGH the van. If the fan is mounted right behind the cab, seems like the rear of the van might get a bit stagnant and be noticeably warmer.
Doing the fillers that I did wasn't that hard. And as mentioned, Hein makes it even easier now with an adapter plate.