If two apartment units “share the same ventilation,” generally where does this intersect? (For instance, the AC would probably only draw from inside each apartment’s own internal air, not from their neighbors’, but when sucking air out of the bathroom vent, they both vent outside with the same vent?)
(It’s an it depends question, of course, but just asking in general)
Well, the idea is that air is always moving toward the roof/outside, either by the simple stack effect of lower air pressure or assisted by a fan on the roof. So, just like shared chimneys, back-to-back bathroom vents feed into the shared vertical exhaust stack. A floor above, two more bathroom vents do the same, and so on.
Conceivably, just the right kind of wind blast could cause air in the exhaust stack to be blown back into your bathroom, and maybe this could include a bit of your neighbor’s exhausted air as well. I live in a 27-story highrise, so we have exhaust fans, and I’ve never known such a thing to happen. On very windy days, though, I can feel air coming out of my bathroom door’s strike plate!
If an AC is shared between two apartments, it would likely be set up like a zoned system. That is, each unit has it’s own vents, returns and t-stat, but the same compressor would turn on regardless of which unit was calling for cooling.
As for bathroom vents, they’re most likely individual fans, and simply have their exhaust connect before exiting the building. Similar to how a house with multiple bathrooms might be set up. In theory, the flapper should keep air from one bathroom out of the neighbors, but it’s not always the case.
The other option is an inline blower that pulls air from multiple unit’s bathrooms, but in that case, I’d wager it’s running 24 hours aday.
Now, having said all that systems like these have to be set up carefully. If there’s a gas/CO leak, fire or some other hazard, shared air handling greatly increases it’s ability to spread from one unit to another.
I’m not sure if code allows systems like this, but I wouldn’t be surprised if it’s not done on new constructions and you’re seeing it on older buildings.
At the college I went to, the dorms were set up like apartments. 7 people to a dorm with 4 bedrooms, 2 bathrooms and a full kitchen. We smoked a lot of pot in those dorms. In the place I typically spent my time, we usually did it in the bathroom so the fan would draw the smoke out (or so we told ourselves). I found out years later that the bathroom in the next dorm over would smell like weed every time we were smoking. Luckily, since the RA lived in that one, they didn’t know where it was coming from so they mostly ignored it.
I can’t imagine apartments on a shared ventilation system. Bathroom exhaust is a different matter. Some have an exhaust fan in each bathroom that works with the light switch, the exhaust from the fart fans are connected to a common duct to the outside. More common is a exhaust fan on the roof running 24/7. The fan is ducted to each bathroom. If the fan stops running for any reason then smells can travel through the duct work from one apartment to another.
Thanks. The reason I asked is because my neighbor’s bathtub is being resurfaced with some strong chemical and I could smell it very powerfully in my apartment. The only two internal culprits I could think of was the bathroom exhaust fan system and my own AC (but surely an AC only draws air from my own apartment, not someone else’s?)
It could just be creeping into the hallway and back into your apartment. Also, your apartment and the other may share some of the same electrical conduit or even just have outlets right on opposite sides of the wall that might allow really strong smells to pass through.
If it’s still going, close your bathroom door and turn on the fan. If it’s coming in that way, that’ll keep it out, if it’s coming in some other way, that should help draw it out.
Yeah, my previous across-the-hall neighbors smoked very stinky pot when they got up at 5 am. The smell would seep through the shared wall (at least two sheets of drywall) and wake me up.
I guess I’m not sure what you’re calling the ventilation system then. Are you thinking of forced-air heating ducts, like the ones so important in No Country For Old Men? I don’t think those are very common.
Supply and return air ducts of the AC system.
I’m sure there’s some example of that somewhere, but that’s generally not how residential AC works. Either each unit has its own through-the-wall, window, or split units; or the building runs chilled water from a central apparatus through pipes, just as a boiler runs steam through pipes to radiators in each unit. What the unit resident controls is merely a fan giving more or less air flow across the chilled pipes.
Do apartments that are on TOP of each other (i.e., 101 on first floor, 201 on second floor) generally share into the same HVAC/ventilation systems and can send vapors from one into another?
Again, that would be rare, perhaps possible if a nonresidential building had been converted by amateurs.
But there are typically a half-dozen plumbing and electrical risers that run vertically through multistory buildings, and it’s not easy to get a completely airtight seal around all of them.
This thread is mixing up heating, cooling, and exhaust air flow systems.
As for bathroom ventilation in multi-unit buildings, if they share exhaust ducts, they should have valves (loose flaps that only open one way) to prevent back-flow from any unit into another, as Joey P mentioned.
But apartments are far from airtight. One way or another, one can always smell what the neighbors are cooking. Or smoking. Or painting their bathtub with.
In my building, I have new next-door neighbors who moved in just yesterday, who are apparently heavy smokers. In less than 24 hours, my apartment smells like a motel room, with the typical ambient scent of stale smoke. Yecch.