Doing a reno job in a condo, we gutted the bathroom that had a common
duct riser for the condos above. I don't know if there is a fan on the
roof or not. But Is there any reason I can't put in a vent fan of my
own to force the air up this duct? I believe the duct is made of some
kind of concrete, or possibly asbestos? How is this usually dealt
with?
It was originally a wall vent, so I would have to get a wall mount
fan.

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** If the duct is common to several units, and was made for bathroom
ventilation, I would expect there is a roof mounted blower. If you connect
your own fan to the duct, and there is nothing pulling the air up, and
there are no backflow preventers, your air is going to go into other units


*If there is a roof mounted fan, there is no guarantee that it is actually
in working order. Some roof mounted items don't always get proper
maintenance. Find out from condo management if there is a fan and if it is
working.