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.