I'm surprised it damaged the sheathing. I found in my previous house that
they were just dumping into the attic for many years with no apparent
damage. Your attic probably has inadequate ventilation. Fans are available
in different sizes but some require bigger duct work which you probably
don't want to change now. You might be better off just hooking a timer
switch in so the fan stays on 15 minutes after your shower is done and then
turns off automatically. They sell fan timers where they sell the fans.


"jay" wrote in message
news:_ADJd.20374$rs2.6071@trndny07...
It is not a common setup and may be prohibited.
It *is* done though but the results are unpredictable.
Each fan normally has some kind of "flapper" valve
inside to prevent backdrafting. You could see if
that is present and working.

Thanks. Will look into this. Most likely there is no flapper. These are
Broan fans if that means anything to you. Perhaps, the flapper, if
present, doesn't work as well for the master bath's fan because it is
mounted sideways in a skylight's opening, rather than on the ceiling. It
could be that, when idle, the flow from the 2nd fan, although powerful
enough to make the blades spin, still isn't powerful enough to close the
flapper, but I'd bet that the flapper is just absent. Will see what I can
find.

In the end, I suspect that it won't be a big problem;
see what your "steam test" shows.

But you paid for it; it's your call...

Thanks. I will see what happens with the steam test. By the way, cross
flow from the active to the idle fan, although it obviously exists, seems
relatively weak when I hold my hand near the idle fan. I will try the
steam test and see if this issue really is a problem or not.

By the way, even though I just spent close to $300 extending the exhausts,
I'm skeptical that these fans, even when properly installed, really help
that much. These Broan fans, even though they SOUND like they work, each
can BARELY cause a sheet or two of toilet paper to defy gravity if I place
a piece or two across the opening. In other words, I'm skeptical that
these fans really suck enough air to get rid of anywhere near ALL the
excess moisture/humidity when taking a shower. Perhaps it's only 25% of
the excess moisture/humidity tops.

Jeff