bathroom fan

If you're in an apartment building and there's no window in your bathroom, the building has to provide mechanical ventilation via an exhaust fan, usually on the roof.

If the super or landlord doesn't respond, call 311.

I agree with NWT - sounds like the central toilet exhaust fan on the roof is not working. (It should be drawing air out through the vents in your bathroom and the others in your vertical line.)

If you are determined to modify the vent, the component you're describing is called a backflow damper or backdraft damper.

But you shouldn't buy or install anything yourself. That's the building's responsibility.
What's coming out of there in the air is not good.

311 will connect you to the HPD. They will send an inpector who will issue a violation. He will do the tissue-test.
The HPD will send a nov. (notice of violation) to the building managment co. They will be given time to repair it before an inspector returns to verify that the violation has been repaired.

Airflow should not be reversing. The ventilation system is sucking in, and then it's blowing the sucked stuff back out at you. That sucks.

most old buildings have just a vent pipe connected to the roof without any mechanic fan. you can install your own fan using the existing pipe/duct

a good panasonic whisper fan cost under $100, hire a handy man cost $200~$300 to install

Thanks for the suggestions. The problem doesn't happen all the time - just occasionally, and never when the handyman's around. I suspect the fact that I'm on a lower floor of an almost 50 story building has something to do with it. The suction - even when its flowing the right direction - is not very strong. I'm leaning towards a powered fan, but am reticent about the added wiring to power it.

in highrises they are suppose to have a fan on top and on the bottom so that the people on lower floors get the benefit as well. as for the wiring, if you are not tiled to the ceiling, it should not be an issue.

You can't add anything to the hvac, even if you're handy. Need to clear it w/ your building and they must repair it. It's a violation. and unhealthy.

Meanwhile, you can do the tissue test:
Open tissue
place against the vent
remove your hand
it should stick up there if the intake is sufficient.

caonima, I saw your comment here and in another thread about the lack of proper ventilation in NYC bathrooms. I am having the same problem in my coop building. I have a vent in the ceiling, but no fan. I looked at the panasonic whisper fans, but I'm not sure how they should be installed, as the outtake on the fan is on the side, whereas the ducting on the existing vent goes up. any advice you can offer??