The picture is of the gas hot water heater vent pipe. The hot water tank is just on the other side of the wall.
It runs almost level, and it appears to be single wall pipe.
It was enclosed
(screwed shut) in a small enclosure in the bathroom. The gas was off to this unit so I didn't go any further with it. No louvered doors or vents to draw fresh air from.
Is this acceptable?
Thanks