Can I drill new holes in exhaust fan housing for mounting purposes?
February 26, 2018 7:22 AM   Subscribe

I want to install a new fan without cutting out part of the ceiling, but most new fans that fit in the existing hole have tabs that extend outside the housing for mounting purposes. Is it sound to drill new holes directly in the side of the housing so that I can attach it to the joists from the inside or will that compromise the integrity of the unit?

We need to replace the exhaust fan in our half-bath. The old one is irreparable and long discontinued. The ceiling is hung underneath another ceiling (!!!) by framing with pseudo-joists that are roughly 7.65" (!!!) apart. There is no access from above. The ductwork is semi-rigid and fully extended. The arrangement is, say it with me, suboptimal.

This is a 1915 rowhome in Philadelphia, for context. Remodeled by previous owners to retain as much of the original character as possible, with a number of corners cut. The project list keeps growing, so we're looking to minimize the scope of each individual endeavor.
posted by grumpybear69 to Home & Garden (9 answers total)
I wouldn't have a problem doing this. Just make sure whatever holes you drill are sealed well so as not to reduce the airflow. Also make sure the screw heads aren't going to interfere with the fan itself.

Of course this is not the right way to do it but installing new stuff in old homes often requires doing sub-optimal things. I am not an electrician, HVAC tech, or contractor. I have Mickey Moused the shit out of a lot of things in my day, however.

Before I did anything, I would make absolutely sure the ductwork and electrical supply is compatible with my new fan. That means that you'll be able to properly connect the ducts without tearing apart your ceiling and that the electrical cables are long enough to connect to the new fan and there's a way to properly ground it.
posted by bondcliff at 7:32 AM on February 26, 2018 [4 favorites]

Should be OK as long as you pay attention to possible fouling of the fan blades by screw heads, possibly requiring the use of countersunk screws.

But have you closely examined your proposed replacement fan? The point of the tab-type mountings is that they don't need access from the ceiling side; the tabs slide in and out, so you just slide them all the way in, then loosen the mounting screws until the tabs are as far behind the mounting flange as you need them to be given the thickness of the ceiling plaster, then reach through the ceiling hole to plug the fan into its supply socket, then push the fan into the hole, then slide the tabs out, then tighten the mounting screws. Even if the fan is a tight fit between pseudo-joists, it should be possible to find an orientation that lets the mounting tabs do their job.
posted by flabdablet at 7:32 AM on February 26, 2018 [1 favorite]

@bondcliff - the ductwork is 4" and all of the fans I'm looking at are 4" as well. There's already a romex connector on the electrical wiring and enough slack to attach it prior to installation, presuming the wires attach on side opposite from the duct. So, more limitations, unless I want to extend the electrical wires. As for grounding, I'm not sure - the last fan had the grounding wire hooked up to a screw in the housing itself, which, meh?

@flabdablet - I'm still scouting out fans online, so my ability to examine them is limited. Delta Breez looks like the best quality and has the best instructions but is also way too quiet for a first-floor half-bath near a kitchen, so it will likely be an Air King at a mighty 4 sones, though of course they have the A/C port on the same side as the duct. There is a Delta Breez with a bluetooth speaker which could be nice but I'm unsure if I want to permanently mount a small entertainment tablet in a bathroom, you know?
posted by grumpybear69 at 7:50 AM on February 26, 2018

the last fan had the grounding wire hooked up to a screw in the housing itself

That's what you want. Just make sure the ground connection is secure.
posted by bondcliff at 8:06 AM on February 26, 2018 [3 favorites]

Related follow-up question: if we need to extend the Romex (since the only fan that fits and is loud enough has the @#&@# wire hole on the wrong side) it sounds like, in order to be code-compliant, we'll need to install a rework box to handle the splice, which means another hole in the ceiling since you can't bury splices. Is that a correct assumption?
posted by grumpybear69 at 10:47 AM on February 26, 2018

Yes, any splices need to be done inside a junction box, though now we're dangerously into "you probably shouldn't be listening to some guy on the internet who has done some home wiring but not enough to be offering advice" territory.
posted by bondcliff at 11:19 AM on February 26, 2018 [1 favorite]

grumpybear69: "The old one is irreparable and long discontinued."

If it's the motor or blade that is gone, and if you haven't already, take it to a motor shop. I've had them supply new motors for 60 year old kit at times.

If you need to go new: Drill your holes near the corners of the housing and try to put holes opposite from each other shimming the width of the fan with wood if possible.

grumpybear69: " As for grounding, I'm not sure - the last fan had the grounding wire hooked up to a screw in the housing itself, which, meh?"

Normal. All modern fans are going to have a specific screw for doing this if they don't have an attached green wire.

grumpybear69: "we'll need to install a rework box to handle the splice, which means another hole in the ceiling since you can't bury splices. Is that a correct assumption?"

Yes. But you can put the box close to the fan and then disguise it with an over size fan grill. And while you've got the large hole in the ceiling from the fan you might find it easier to install a new work box right to the joist
posted by Mitheral at 10:14 PM on February 26, 2018

I just installed a Delta Breez fan. It already had holes on the inside for mounting to a joist.

Also, there is a type of splice rated for being hidden behind walls.
posted by flimflam at 12:30 AM on February 27, 2018

Thank you all for your input! We ended up going with a cheap Continental Fan unit that ran $25. It had the holes in the right places for everything but mounting. Ended up having to use the external mounts intended for new ceilings after all since there was no way to drill holes in the housing. Thankfully the unit was just small enough to allow sliding it in at an odd angle. On the bright side I now have a right-angle drill adapter!
posted by grumpybear69 at 1:29 PM on March 28, 2018

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