Replace the duct hose for bathroom exhaust fan, what kind to use?

10 years ago

I am going to replace the exhaust fan in my bathroom (it is located in the side of the soffit that is above my tub, and was wondering what type of duct work is best to use to connect the fan to the opening in the wall to the outside?

Right now, there is about a 3-foot piece of ridged flexible hosing, that kind of resembles a vacuum hose, only 3" wide. It was actually disconnect from the fan when I looked inside. It must have worked it's way loose over the years.

I was wondering if this is the best type of hose to use? Or maybe a rigid type of smooth duct work would be better?

I took a quick look on the Home Depot website, and they don't seem to have any specific type of duct work or hosing for bathroom exhaust fans that I could find.

The do have some flexible hosing (some that are insulated too).

What would be best?

Thanks!

This post was edited by Frizzle71 on Thu, Jun 13, 13 at 1:26

Featured Answer

xedos

10 years ago

Ridgid is really the only way to go especially over long runs.

We usually spec 4" sched. 20 PVC pipe as it comes in longer lengths than 4" metal does around here , though elbows can be tough to source sometimes.

Unfortunately most contractors / HVAC guys will use flexible corrugated hose because it's cheap and fast. If it's a luxury project they'll splurge for the flex aluminum instead of the plastic kind. This type of pipe can cut a fan' effectiveness in half over long runs. Little thought is really given to these fans in most homes today. They are often undersized for a given bathroom and poorly located too. The crappy pipe detailing makes a bad situation worse.

Panasonic's website has (or used to) a pretty good tutorial on how to properly size a fan, where to locate it and how to properly pipe it to the outside.

I think much of the problem is cost and ignorance. Most people know you get a fan in your bath , but when pressed they won't really be able to tell you its there to expel warm moist air from your home, not smells. They assume that the $34.95 version will be fine for them and a quick & dirty install will get ya out the door for a hundred bucks. The reality is, many master baths, and some hard working kids baths need a much larger fan than 35 bucks can buy. We are often talking $100-$200 for an adequate model, more if you want features or quietness. Add the increased piping cost and labor for the proper venting needed on higher capacity fans and this can quickly become a $500 line item - which starts to look crazy for something as pedestrian looking as a bath fan.

Timer switches are also a very good idea as most fans even properly sized ones need to run a while after you've left the bath to completely exhaust the moist air.

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Comments (13)

geoffrey_b
10 years ago
You can use a dryer hose and a clamp. After attaching the hose - use some duct tape to seal the connection.

If the entire run of hose is only 3' long - no sense in using an insulated duct.

If the old hose is in good shape, reuse it.
live_wire_oak
10 years ago
Rigid 4" ducting, insulated, and NOT terminating in the soffit or attic would be the correct way to do it..
enduring
10 years ago
Jumping in here. Live Wire Oak, why the rigid duct and not the flexible insulated kind that is found at Lowes and HD? I have to get ducting for my fan and was thinking of the insulated flexible kind. I would run it tight (without sags).

Thanks.
catbuilder
10 years ago
Smooth rigid is always best. Flexible duct creates way more resistance to air flow.

And, please, don't ever think about using flexible hose on a dryer. Lint catches on all the ridges and creates a fire hazard.
enduring
10 years ago
Catbuilder, Thanks for the information. I think I will use rigid then, in my exhaust fan situation. I have rigid for my dryer exhaust with the seams headed in the correct direction so lint has a harder time catching. No screws, only taped ends :)
Frizzle71
Original Author
10 years ago
Thank you all for the information!
Jon
7 years ago
Alright, I know I am jumping on an old thread, but I am trying to figure out this "rigid insulated ducting" thing. And if live_wire_oak is still on these boards, I'd love your expertise.

For rigid insulated ducting, should I use a product like:

1) Round Metal Duct Pipe (http://www.homedepot.com/p/4-in-x-5-ft-Round-Metal-Duct-Pipe-CP4X60/100196725?storeId=10051&langId=-1&catalogId=10053) and add insulated duct wrap?

or

2) MKE 4" HVAC ducting (http://www.homedepot.com/p/Thermaflex-MKE-4-in-x-25-ft-HVAC-Ducting-R8-0-0582-0400-0001/203766760)

Any thoughts?
enduring
7 years ago
last modified: 7 years ago
I'm not Live-Wire, but the second link you posted is flexible duct. That was not recommended by the contributors to this thread. I used rigid in my fan, then wrapped insulation around it. I forget what kind of insulation. I had my son do it. I might have taken the insulation off of plastic ducting and wrapped it on the rigid, and taping with the foil duct tape.
homepro01
7 years ago
last modified: 7 years ago
The duct posted in #2 is insulaed duct and will work for areas where you need to curve or bend the duct work. This is what Hvac contractors use. They also sell insulated metal duct works. Try someone like supplyhouse.com for examples.

Updated link for the ducting on supplyhouse

Good luck!
John Madison
5 years ago
Just FYI, but heavy=moisture laden air from the bathroom is (obviously) intended to be sent outside the home and not just in the attic space, which is why one should use insulated rigid ducting to that "outside space". To do otherwise would permit that moisture to hang in the attic and cause mold/mildew, etc. Remember too that in some areas the condensation of the moisture-laden air will frequently occur within the piping, hence you'll need to gently angle the slope of the ducting so it will drip outside the home. The problem with flexible ducts is that sometimes they will form low pockets, where moisture accumulates and becomes a breeding ground for molds and bacteria.
Jim
5 years ago
last modified: 5 years ago
Can you tell me where / what brand of insulated rigid ducting I should purchase for the bathroom fan to exhaust through the exterior of the house? Is semi rigid acceptable?
Rick Young
3 years ago
I have installed a bathroom fan into an old home that previously did not have one. I have no attic access so I am going down and interior wall and out the rim hoist of the basement. I cannot get the 4”aluminum semi rigid un-insulated duct to fish down the wall without tearing and I am not able to fit rigid pipe up due to space. Can I use a 4” shop vac hose? Plastic would prevent condensation that may occur with the aluminum and it’s less likely to be damaged going down the wall. Or can I split the 4” with a y-connector and run two smaller size duct work down and out?