When you search this topic, over 1,000 responses show up--none of them seemed to address this question so I'll give it a shot:
Why do we put big roof vents in teardrops?
This weekend found me shoping for a roof vent as it's something you should probably have in-hand before you work the spars on the top too much. You want to rough-in the framing to support the vent. If it has a fan, you want to run wire to it. It struck me that I didn't know why we install such huge vents in our teardrops.
There is a roof vent in the Camping World catalog that goes into a 6-1/2 inch diameter hole. It moves 100 cfm of air. By my rough math, our 5-wide by 8-long by 4-high teardrop, minus the galley and considering the curve, might be between 75 and 100 cubic feet. That means we can clean out the air in it in about a minute.
If you put a 14- by 14-inch roof vent, the effect is greater. I found one fan that, on the low setting, it could move 685 cfm. It could move all of the air out of our tear in about 10-seconds! High setting would be about half that.
Sure, we all want to keep carbon monoxide poisioning from happening. We're planning to put windows in each door--it would seem reasonable to think that we could get a cross-draft working to keep oxygen in our brains.
In looking at the piece on RV Crazy, only about half the tears had roof vents in them.
Is the vent there as a skylight? Is it there for fresh air? Is it there as yet another way to admit moisture? Am I pondering this too much?
What say you members of the Teardrop Braintrust?