"djay" wrote in message
news:m%nCj.8985$HA3.8232@trnddc02...
I'm installing a Panasonic bathroom exhaust fan - approx fan box size is
12 X 12 inches and it's replacing a POS nutone NOISE maker that has an
opening about 8 X 10. Panasonic has an approx 1" lip on the underside
that would normally screw right to ceiling joists for new construction
(would need to add a 2X4 to make the 12" span instead of the normal 16".
Anyway, I'm in a quandary as to how to correctly install this fan.



It came with "joist spanners" that seem flimsy and possibly difficult to
install. Alternatively it has mounting screw holes in the lip. I want to
just cut out the old fan and expand the hole (I have been up in the attic
and inspected. the existing joist/electrical etc before doing so). One
side of the existing fan is already attached to a ceiling joist. I'd
still use this point as a starting point and expand the drywall hole away
from that existing joist accordingly to fit the new Panisonic box. My
goal is to just cut the hole, install an new spanner joist to snug up to
the other side of the box (would cross between the headers of the two
existing walls) and just use some longer pan head wood screws to screw up
through the "lip" with mounting holes right through the existing drywall
ceiling and into the old existing joist and the newly install joist.

So in my example above after the new hole is cut into the drywall fit the
larger fan, and new joist installed (parallel to the existing joist but
for the other side of the fan hole). I'd push the new fan up through this
hole until the mounting lip rested on the ceiling. I'd put screws in
through this lip, up into the drywall and into the joist above. Then of
course seal in the fan from above and replace the 3" exhaust duct with 4".
Does that sound doable? I guess normally this lip would be between the
ceiling drywall and joist but I can't see a downside to installing it
directly onto the existing drywall.



That's usually how I do it, but without adding any additional wood bracing.
On the side of the fan housing that will be against the existing joist I
drill a screw hole about three quarters up near each corner. I use them to
screw the fan housing to the side of the joist. I also screw that bottom
lip in from underneath. That gets the housing up solid enough to where you
almost don't need the spanning brace, but I use it anyway.

The joist spanners that came with the Panasonic fan are quite solid. You
will only need to install one. I usually attach the U bracket loosely on
the side that does not have the duct connector. That makes it easier to
slide the joist spanner in while up in the attic. You can snug up the
screws after the spanner is in place.

When cutting the hole in the ceiling, make a notch for the U bracket. Also
on the side that the duct connector will attach the hole must be almost the
full size of the lip so that the duct connector can seat properly. The
finish trim is big enough to cover the larger opening.

Don't forget to use the thumb screw to secure the duct connector to the
housing. There is a little hole near the internal electrical plug that it
goes into.

I recommend that you use knee pads and a dust mask.