Tony\ said:
Ventline VP-543 12V Smoke Van Roof Air Vent
I installed one of these in my pickup topper...and it works OK there. Let me tell you a few things about these fans. If not helpful to you, then maybe others will find this information useful.
First off, they use a very inefficient and noisy straight (or slightly curved) blade centrifugal impeller. It's not really a 'fan' in the conventional sense. More like a 'blower'. Straight blade centrifugal impellers typically can't ever be used for intake...if you reverse the polarity and the motor runs backwards, it will STILL push the air out.
They only have one speed. So, I added a dropping resistor and a 2-way switch so that I can have a LOW setting.
They use a 12v 'hobby motor'...not a brushless motor like the other fans we have been talking about here.
'Hobby motor' is the term used for these super cheap brush-type motors that you often find in some cheap battery-operated toys. Typically the lifespan of a good quality brushless motor with ball bearings will be decades, but a 'hobby motor' will have cheap brass or copper brushes and steel or brass shaft bushings, and will have a lifespan of a year or two depending on how much it is used..or maybe years if it is used sparingly. So they do sell replacement motors...for around $50 last time I checked...and it's a $2 made-in-china motor.
These Ventline fans actually work OK for a vent in a bathroom, where it will be used for 10 or 15 minutes a day, but for overnight use, 8 hours or so while sleeping, they will drive you nuts being so noisy and they wont last very long.
So as long as you know all that BEFORE you cut that 6" round opening, I say, give it a go!