When I attatch the pvc elblow to the top of water heater it is touching the bottom of the joists. The problem is I then need to run the vent along the bottom of the joists for 10 feet then turn between the joists for another twelve feet. The first run wont have any upward pitch, in fact it would need to drop about 1 1/2 inches and then once it got to the turn the next run would rise 5 inches between the joists. Since the exhaust is being pushed by a fan is that small decline in the first leg exceptable. My gut instinct says the 3″ pvc vent pipe should be pitched upward but I’m not sure how I’ll be able to do that. Does it?