Ceiling too short for exhaust fan

Submitted by fancypanting t3_10fs5ma in DIY

I am retrofitting a new bathroom (< 50 sqft). I have 2 problems.

The major problem is from the cut out hole I see the ceiling is only 3 inches deep, while the smallest exhaust fans I can find are 3.6 to 4 inches high. There is a duct or metal sheathing above the hole I cut. The sheathing comes ~1in down on the joist, on both sides of the joist.

I found this thread https://www.doityourself.com/forum/lighting-light-fixtures-ceiling-exhaust-fans/496103-ceiling-fan-box-higher-than-ceiling.html from 2013, which suggests to unscrew the motor from the box and attach to joist directly. This is the manual https://www.manualslib.com/manual/2278228/Hampton-Bay-Bpt12-13e.html?page=10#manual, it does not appear there is any place for screws on the motor itself.

The minor problem is that the 4 inch high vent uses 3 inch exhaust pipe, but I have 4 inch pipe installed. I would presume a 3-4 increaser/reducer would solve the problem. I have also bought a 4 inch pipe exhaust fan, but that one is 5.25 inches high which would protrude further down.

Please suggest what I could do. There is a drop ceiling just 2 ft beside the hole so I wasn't expect there to be any duct. What if I just leave it hang below the ceiling? Anything I need to do for the gap? It's a 8 feet ceiling with exhaust vent retrofitted to be under the ceiling along the corner.

EDIT for in line duct fan, how to connect the grille and elbow if the ceiling space is 3 inches? No space to turn vertically over the ceiling space.

2 WEEK UPDATE: went ahead with an inline duct and grille cover. Works great! Quiet and affordable

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Comments

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JerseyWiseguy t1_j4yokpd wrote

If space is tight, you can always use an inline duct fan anywhere on the duct. Then, you can just attach the duct to the ceiling and put a generic grille over it.

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fancypanting OP t1_j4ys1sx wrote

Thanks for your reply! I deleted my previous comment as I now understand what you mean. I will definitely keep this in mind.

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LeKy411 t1_j50ng3i wrote

We have one bathroom with an inline duct fan. We didn't realize there was no bathroom vent when we bought the house and there wasn't a great way to run a separate switch since everything is in conduit so the fan turns on with the bathroom recessed lights. The inline fan is so quiet I love it and will probably put in another one in our master bath once the current fan dies.

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fancypanting OP t1_j516d8r wrote

is the electric same as an exhaust fan, with its own switch and everything?
EDIT: I am seeing a lot with a plug

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JerseyWiseguy t1_j51kyde wrote

There are different types. I've seen some with plugs and some without. Even if it has a wired plug, you can still remove the plug and wire it directly, or install an outlet and plug it in. I installed one in a duct that went from a bathroom through an attic and out through the roof, and rather than have the fan in the ceiling, I installed it in the attic (super quiet in the bathroom!), plugged into an outlet in the attic that was controlled by a switch in the bathroom. I also installed one in a bathroom ceiling and direct-wired it to the existing wire that was already controlled by a switch.

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fancypanting OP t1_j51oz1u wrote

The main problem is how do I connect the grille to the vent? It's difficult to have an elbow inside the 3" ceiling space and if I have it on the wall I might as well just use a larger CFM wall-mount

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Mindless_Fill_3473 t1_j4yw57i wrote

I put my vent in a wall once bc there wasn't enough room in the ceiling, worked great.

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Yummy-Beetle-Juice t1_j4z53s3 wrote

Just a thought... Can you install trim around the fanbox? You can then lower the fan assembly by up to 3/4" depending on the thickness of the trim boards. The only issue would be where the duct attaches to the fanbox.

If you get aluminum duct, you can push it oval so it will fit.

If you do it right, it might look good.

I did not see anything in your post about running electrical and a switch.

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Yummy-Beetle-Juice t1_j4z5clb wrote

Another possibility is to install joists and bring the entire ceiling down.

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fancypanting OP t1_j4zchwf wrote

If I want to go with the 5.25 inch tall fan, that would be too much right? Lowering by over 2 inches below the ceiling? Actually the hole isn't big enough for me to test placing the fan in place, but I'll enlarge it tomorrow (for the 4 inch tall fan).

The electrical I have managed to run through the hole along the joist to the other side of the bathroom.

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Yummy-Beetle-Juice t1_j5030ze wrote

Can you cut a hole through the sheathing that is nailed on top of the rafters? Is it the roof deck? If it is the roof deck, do not disturb it. Look in the attic before doing any work.

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fancypanting OP t1_j517fhm wrote

the bathroom is below another floor. I am not too confident to cut through the sheathing, fearing that it is the heating vent or something else important.

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Yummy-Beetle-Juice t1_j543lo3 wrote

Probably not a good idea then. If the bathroom is on the first story, how are you going to run the fan exhaust duct to the outside? How are you going to run electrical?

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fancypanting OP t1_j547vi4 wrote

the fan exhaust duct is already in place, it's outside the drywall so I have to later fix them in place and cover them up with plywood.

what do you mean how to run the electrical? I just take it from the living room?

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crow-milk t1_j53fvxs wrote

It looks like Panasonic has a 80-100cfm fan or fan/light that’s 3 3/8 deep. Really good exhaust fans but if you’re going to wire one in you need a good grasp on electrical. 120v constant hot gets fed into the fan, low voltage switch loop to the switch on all the ones I’ve used.

FV-0810RSL1

Worst case if you have a firm 3” restriction you could fir down the opening with some s4s trim.

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fancypanting OP t1_j53s7n3 wrote

I heard Panasonic ones are more expensive. Tomorrow I'm getting an 100CFM inline duct fan and grille and try it out first. I have recently moved a thermostat across a few studs, but I haven't added switch + fixture before. I watched a video yesterday and will watch again and take notes so I don't mess up the electric.

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fredsam25 t1_j4zxrrb wrote

You could always do a roof mounted vent fan. It gets mounted above your roof, and you only need the grille and duct mounted to your ceiling.

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