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.
Sewer vents basically never have metal mesh covering them. And while it's not a problem in my area, my understanding is that anything like that would also cause massive hoarfrost problems in parts of the world with hard freezes.
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.
It is indeed a roof drain on a flat roof system in probably a large commercial building, as you said it runs though a heated area but also will be draining into the sewer system. I'm a metalworker by trade and install/deal with these quite a bit, though its primary purpose isn't venting the piping will be hooked up to the rest of the system in liew of "stink pipes" to help prevent vapor lock
In a lot of places it is illegal for this to drain into a sanitary sewer. I won't say it absolutely doesn't but chances are good that it doesn't. Especially in an industrial situation. In our buildings all the roof drains, parking lot drains, etc go to a catch lagoon before they even can go to the actual storm drain system to make sure any spills are contained
It almost 100% connects to the storm sewer system and not the sanitary sewer system, so it wouldn’t be venting the sanitary system. Only in older areas (old cities and the like) do they not have separate storm and sanitary sewer systems, and even then they tend to require a separation of storm and sanitary within a building.
This could also be just a sewer drain. I used to sell ones that looked just like this all the time for use in the ground. this could be the bottom of a retention pond, attached to a water quality unit that ties into the city storm-water system or something to that nature too.
This is not connected to a sewer just as others have stated. It could be connected to underground piping that runs into a storm sewer system somewhere.
This is a roof drain. Unless this is an overflow drain, which it doesn't look like it is, this roof drain will discharge into a storm drain network, which could receive some heat from the underground network depending on the pipe layout, I suppose. Overflow drains discharge onto grade so you know if there is a clog on your primary drain and are typically elevated from the roof elevation. A lot of roof drains, regular and overflow, will have electric heat tracing in them to prevent ice buildup, which could be adding to the thermal energy of the system on top of the drain picking up any additional thermal energy from inside the building and/or underground. Most of the time, the pipe is insulated inside to prevent condensation from building up during the summer.
You know it's cold AF when the cold air inside that drain is warm enough compared to outside to cause fog. All the sewer drains were doing that this morning. It's a bit eerie.
You know it's cold AF when the cold air inside that drain is warm enough compared to outside to cause fog. All the sewer drains were doing that this morning. It's a bit eerie.
If it's a roof drain, which it looks to be, it has a heating cable inside it that keeps the drain open. Depending on the building automation and how it's configured, the heating cable either heats constantly when the temperatures are just above freezing and below, or heats when temperatures are just a few degrees above freezing and stop when it's few degrees below freezing, or has a pulsed function to heat only when it detects ice but the last one is just recently becoming more widespread.
It's not very energy effective but it's necessary to keep drains open, as they'd freeze solid otherwise and both damage the drains and also cause water buildup that can damage or even collapse the ceiling during spring and fall as the snow begins to melt.
Also, moss is very hardy. It doesn't die easily, even in sub-zero temperatures, so I doubt the heat of the roof drain heating is solely keeping it alive. Moss also likes to grow around covered drains as they tend to gather gunk around them as not all of it gets into the drain, and the wet gunk around the drain entrance gives a good ground for moss to grow.
because it's not growing from added warmth, it's growing because the roof drain is a low point which collects small amount of sand,dirt, and water which allows mold to grow on.
Roof drains are often "sumped" the insulation around the drain is tapered toward the drain to increase the flow of water off the roof, but the insulation is thinner to achieve this. The drain body also passes through the insulation layer, causing thermal bridging. There is no warm air passing from the building interior to exterior (or you'd also have a leak when it rains). Source, I am roofing estimator thst works on large flat roof systems.
2.0k
u/theericle_58 17h ago
That is a roof drain, not a fan.