I have noticed in my area most water haters and furnaces are gas and use Bvent. It also appears (driving around looking) most use the 3 rule, if it’s 3 ft above roof it’s o.k. Also how long of run can you have, another house I looked at only the water heater was on this approx 15’ straight up then 14’ of 30degrees then 6’ up thru roof. I was curious about draft on this.
No. It’s an exhaust vent, not a chimney.
I don’t have the exact requirements in front of me, but generally it’s 12" minimum projection above the roofline. Also, the vent should be extended above any window or vertical wall within 8’ of the vent.