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.

Rigid 4" ducting, insulated, and NOT terminating in the soffit or attic would be the correct way to do it..

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.

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.

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 :)

Thank you all for the information!

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?

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.

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!

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.

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?

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?