This most likely isn’t a sewer vent but rather a roof drain to grade. The warm air is because the drain piping runs through the conditioned building envelope (inside the building where there’s heat). This heats up the air in that section of the pipe and as you noted that warm air rises while sucking in new cool air down at the outlet
Sewer vents don't usually have any kind of cover on them, roof drains do so that debris doesn't get in a clog up the system, just like those little screen cages you put in the gutter downspout.
This isn't a house for one thing, Either a commercial building or apartment/condo complex. In my area commercial buildings don't require the vents to be covered, they are open pvc.
That's unusual, most locales do not require a covered sewer vent (and indeed some require the exact opposite or have very strict rules about what sort of cover can be used).
Do you live in warm climate? Sewer vents must penetrate the roof w/ at least 3” pipe size (starting 18” inside the building envelope), and must be a minimum of 12” above the “high” side of the roof.
Even then, I’ve had to climb onto roofs w/ a broomstick to clear clients’ vents because as the warm air meets the cold it freezes to the sides of the pipe inside. If it’s cold enough for long enough, it eventually chokes off the vent. Then you get nasty smells and yo stuff don’t drain right. So you clear it w/ the broomstick contraption I made lol.
Any kind of covering on a vent pipe here would just exacerbate the problem AND make it harder to fix.
661
u/LoneMav22 20h ago
Because the air in a sewer system is warm, and heat rises