Sorry Dodgeman, but I was thinking of my Natural Gas HWH vent. With it, I go out the sill plate and use PVC in an 'S'. It must vent-out / terminate at a 3' height from the ground.
Initially, I was thinking about the dryer, which is gas-fired too, in terms of venting that, and I managed to confuse it with the HWH. With the dryer vent, there was no 3' requirement. (But w/the HWH, there is.)
Thanks much for bringing it up. And I'm sorry for keeping you awake while waiting for an answer from me. LOL