ᐅ Exhaust Ventilation in Guest Bathroom – Unpleasant Odors Flowing Back In

Hello,
I have just moved into a new apartment on the third floor. The guest toilet is fairly simple and located inside the building.
There is an exhaust fan that can be manually operated with a timer switch (up to 15 minutes).
Above the toilet, there is a vent in the wall (100mm (4 inches) pipe with a simple square grille). Behind it is a fan controlled by the timer switch.
The two apartments below also have a guest toilet in the same spot. Apparently, the neighbors use it quite often for their heavier business... and since the exhaust pipe runs vertically throughout the entire building, unpleasant odors from the neighbors are rising up to our apartment... No matter when I use the guest toilet, it smells very strong.
My question is: Is it possible to install a valve instead of the louvered cover on my 100mm (4 inches) pipe in the wall so that air can only be drawn outwards (into the exhaust pipe) and not flow from the pipe back into my apartment?
The fan is not very powerful – is there anything I should consider when buying such a valve or an “air trap” (I’m not sure what this kind of device is called)?
Thank you very much for your help!
Best regards from Ba-Wü
Christian

You need a bathroom fan backdraft damper for a 100 mm (4 inch) pipe; it is installed inside the pipe. This way, the air can only flow in one direction.

I'm just surprised that this wasn’t installed in your apartment. The last time I encountered a system without a backdraft damper was in a student dormitory, where a guy two floors below was growing marijuana in his bathroom and venting it through the fan—you wouldn’t want to know how bad my bathroom smelled then.

Apparently, it was a so-called "Super Skunk" grow—nomen est omen!

Thanks for the great tip, Pinky0301!
That’s exactly what I was looking for! Awesome!
This also works if there is no strong draft coming from the other apartment into mine (so the flap closes), right?! Thanks

Scout schrieb:

You need a bathroom fan backdraft damper for 100 mm (4 inches), which goes inside the pipe. This way, the air can only flow in one direction.

I removed the cover (see photos) and found the backdraft damper online. THANK YOU!
Can you simply install such a damper inside the grey pipe?
The fan is located behind the backdraft damper – in photo 4 you can see the riser pipe but not the fan. Does that cause any issues? Does the fan have enough suction to open it?

Sorry for my silly questions – I really have no idea

Where is the fan located? In the riser pipe?
Is there one for all floors, or how does that work?

That might be the case – unfortunately, I have no idea.