Elevating an exhaust fan?
Ceiling exhaust fans seem to be built to fit between the roof framing at the ceiling joists. As such, if you want to vent to a gable end (which seems to be a common recommendation in many places except the fan install instructions), that orientation forces you to introduce at least 2 bends and a right-hand turn to reach the gable.
Since you’re already building headers between the ceiling joists to support the fan, I’m wondering why not just raise the headers and the fan body above the ceiling joists? Doing so would allow you to rotate the unit towards the gable end, eliminating the bends and lateral turn.
Of course you would then have to somehow attach the grille to the ceiling at the hole, and maybe create an insulated box with rigid surrounding the unit (which might even make for better insulation).
Is this workable idea, or am I once again overcomplicating things?
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Replies
Tiziano,
Rather than go to a gable end, If the soffits are boxed-in the easiest place to exhaust is near the fascia using a directional termination that will throw the air past the overhang.
However, I now do something similar to what you are proposing for different reasons. To both make air-sealing the fan enclosure simpler, and to keep the duct connection easily accessible if the unit needs changing, I mount bathroom fans in an air-sealed box. You could easily make it taller and do what you described. You do need to buy a separate, larger vent cover.
That's pretty neat, Malcolm. The box looks to be rigid foam, unless I'm misreading the photos.
I'm guessing that once raised (even if going through the soffit) there would be an easier time insulating too. For example, if I'm doing R-49 (13 3/4") batts and I raise the bottom of the unit enough to clear the batts, the vent piping would not displace them and hose up ( :) ) that bay's insulation.
Of course I'd still wrap the pipe and slope it downwards to the soffit area. Which brings up a challenge - the soffit/attic junction. Even with a 12" raised heel that pipe has to slope enough to get into the soffit cavity.
See what I did there? Complicating again.
Tiziano,
The box is plywood, sealed and painted, with a wood face-frame to seal to the ceiling drywall. Foam alone wouldn't work as there would be nothing to mount the fan housing to. I line the outside with foam board if it is going into a roof space. I also use these in the floors between stories.
if you have decent attic access post build, maybe consider an inline exhaust fan...
the motor will be somewhere above the insulation, mounted to whatever is convenient. then at the bathroom ceiling, you use whatever duct boot is applicable and install a backdraft damper as normal. connect a duct, seal everything up, etc.. the duct will also come out of the ceiling in any direction you desire.
but the beauty of it is that you can seal up the ceiling portion and you never have to touch it again . if/when you need to replace the inline motor, you do everything from the attic without having to deal with insulation or have any difficulty air sealing the connections.
it is NOT fun having to replace a standard bathroom exhaust with insulation on the attic floor -- hence Malcolm going the extra mile to make it easier.
cs55,
Very good suggestion! I had forgotten about them. I wonder why they, and the ones that mount on the wall outside, are so expensive?
I only do the boxes where there is no future access (Between floors and cathedral ceilings).
I just did what you suggested at my house. Installed two inline remote bath fans and an inline remote kitchen exhaust fan. I reused the existing fan housings but gutted them to retain the light option and eliminate need to modify the ceilings. The kitchen hood is a microwave that I removed the fan and use the fan wires to switch a relay to operate the remote fan. All are significantly quieter, and move the same (bathrooms) or more air. I mounted them high enough in the attic that when I insulation is added it will still be above. I mounted the fans close to the rooms but am regretting that decision and should have mounted them right at the gable end wall so future access is only a few feet and not halfway through the attic.
wish i had those boxes, i replaced 4 fans in my house... didnt do inline fans. if any of these ever go out and i cant get a new motor/fix it, im going to gut the housing and throw an inline fan in the attic just to not have to redo the ducting/air sealing around the cutout 🤡
random thoughts;
i suppose its possible for the fan to be attached between joists and then buried in insulation, if going out to a gable or soffit.
cs55, I'd considered an inline fan, but once the building is finished I won't have enough attic access to move around. It's only 12' x 16' with a 5/12 roof. That's about 3' high at the gable peak and from that subtract 13" for insulation. I am planning on gable vents though, so maybe I could figure out a way to mount an inline within reach of that?
Malcolm, do you have any pictures of one of your boxes with a fan installed in it? I'm fuzzy about how one gets attached.
At this point, pending a rethink of cs55's inline idea, I'm leaning towards this Panasonic: https://iaq.na.panasonic.com/ventilation/fans/whisperceiling-spot-290-cfm
Comments here raise two questions for me:
1. Assuming I go with that Panasonic, do I still need a backdraft damper? I can't find the source right now, but I think the unit has one in it.
2. Whether Malcolm's box or inline, if the duct is above the ceiling insulation does the duct still need to be wrapped with insulation?
In other news for those who have answered my questions about this project along the way, the piles go in tomorrow so it's about to get real.
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@malcom
"I wonder why they, and the ones that mount on the wall outside, are so expensive"
the kind for bathrooms arent all too bad, $150-200 for the motor. about on par with a better panasonic ceiling model.
the multi port exhaust fans that let you have multiple ceiling vents with 1 motor and 1 roof/wall penetration are kinda on up there.
@tiziano
yea you still need a damper. i have 4 panasonic fans -- 2 whisper warms, whisper green, something that runs at 30 cfm 24/7 for my litterbox closet..
the dampers on all of them are awful. i initially went without them but i just about went mental because wind would open up the roof exhaust flap, go down the duct and cause the built in dampers to make a lot of noise.
bought inline dampers for everything and installed them directly to the roof vent. i never hear them anymore unless theres like 50 mph winds
just make sure you buy one for the correct orientation 😅 horizontal, vertical, etc..
also keep in mind that 90s can cause a lot of noise. one of my whisper warms has no bends at all, just goes like 5 feet to the roof at a slight incline
the other one required a 90 immediately at the housing and its very loud :/
Thanks cs55.
I'd not realized the horizontal/vertical aspect, but it make sense. Doh!
I've no idea how to judge the quality of backdraft dampers. But, this one looks good at least. :)
https://www.amazon.com/FRESH-SPEED-6-Inch-Backdraft-Shutter/dp/B097DQ7DLG/
i've bought and returned half a dozen different dampers and none of them passed a light test. there was always something. a huge gap down the center where it folds, a gap around the perimeter, poor springs, etc.
https://www.famcomfg.com/product/butterfly-backdraft-damper/
these cost a little bit more than cheaper things off of amazon, but they seemed to be the most air tight option i could personally find. since i couldn't see light, i tried blowing air through them with an air compressor nozzle and i couldn't feel much.. not exactly scientific, but better than nothing.
Excellent. I just bought one of their vents too. Thanks.