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.
What do you think?