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Posted by djay on March 14, 2008, 9:45 am
>
>> 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.
That's good advice and is pretty much exactly what I was going to do. I
like the idea of using the screws through the side of the housing... I may
do that if installing the extra wood brace becomes.... "challenging" :)
As the other poster mentioned, I put the plastic fan cover in place and it
looks like it will snug up to the ceiling without a gap. Has that been your
experience too?
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