I just hired my condo management company (a job performed, at my request,
for my unit only, at my own expense, which was almost $300 after tax) to
extend the two upstairs bathroom exhausts so that they exhaust to the
exterior (through the side) of the unit. (These bathroom exhausts were
previously vented directly into the attic before which had been damaging the
roof's sheathing)

I was not expecting it to be done this way, but the two exhausts are very
close in proximity to each other, and the person who did the work decided to
use a shared vent for both exhausts. In other words, what he did was
connect a flexible aluminum duct to each vent, and then used some type of
"T - connector" to join the two ducts together so they are both sharing the
same shared flexible aluminum duct that leads to the exterior the unit.

I happened to notice that when one of the two fans is running, it actually
causes some air flow to be exhausted out of the other bathroom's idle fan.
If the fan in the main bath is running in the main bathroom, I can actually
observe the blades of the fan in the master bath start to spin. Clearly air
is being pushed from the main bath into the master bath when this happens.
If I briefly turn on the master bath's fan and shut it off I can observe it
switch direction after it stops turning in the normal direction.

In the opposite situation (master bath's fan running when the main bath is
idle), the problem, to me, seems like it could be less severe. The blades
do not move in the main bath's fan. There does seem to be a little bit of
air flow though the fan opening, but I suspect not as much as in the
previously described situation.

Anyway, I just want to get opinions on whether or not this is worth
complaining about, or am I just being too picky? It seems to me that if
running one fan causes air to be pushed out of the other fan, this will,
most likely, cause some mosture to be transerred into the other bath (how
much I don't yet know) rather than the exterior. This seems like a less
than ideal setup.

Is this type of shared vent setup for bathroom exhausts considered to be
normal/common?

Which of the following do you recommend:

1) Immediately complain about this to the management company tomorrow, since
clearly there is a problem with the duct setup chosen for this job

OR

2) should I perform a test to see how much steam actually gets into the
master bath when the main bath's fan is running (while showering in the main
bath) BEFORE complaining about this?

OR

3) Do nothing, since this is a common setup, and likely not worth
complaining about.

Let me know what you think.

Thanks,

J.