Hi, I'm installing a condensing central gas heater in my attic. I need 2 vents through the roof, 2" PVC. I bought the vent jacks with reasonably large sheet metal bases and a rubber collar. Composite shingle roof.
I'm wondering if there's an optimal place to put the jacks relative to the nearby laps. Rather than drill up through the roof, should I go up on the roof, measure to the approximate spot, shove the jack in place, and only then drill down from above? I can adjust the positions of the vents within reason.
Or, are these jack designed so that it really doesn't matter where they go in?
If there is an optimum spot, what should I shoot for? Maximum lap? How about relative to the vertical slits that go about halfway through each tile?