Bathroom exhaust ductwork out and then up

[DenverDave]

I have a brick home with a basement bathroom that does not have an exhaust fan. I am going to remodel the bathroom and intend to install an exhaust fan as part of that project. The only feasible way to run an exhaust duct is straight out through the brick wall. However I can't just vent it on the outside of the wall, because depending on the position of the vent I would either be sending bathroom odors into a nice patio area that is used for entertaining, or into a shed where moisture would be an issue. What I'd like to do is run duct out the brick wall into the shed, then straight up and through the patio/shed roof.

My question is whether there is any issue with doing this, and what kind of duct work to run in the shed. Is a simple metal duct acceptable? Does it need to be insulated to avoid issues with condensation/freezing during the winter? Should I port from metal duct to a PVC stack pipe or something like that? The shed is not insulated or heated at all.

 

[Jadnashua]

A couple of things to consider: the overall 'functional' length (this includes the actual length plus a factor for each elbow) must not exceed the maximum for the fan you choose. If the run is very long, or uninsulated, you will get condensation and possibly drips back into the room. The velocity in the duct needs to be high enough and insulated well enough so that the dew point of the air in there is not reached...something that can be hard to do if the run is long or the insulation is not adequate. Some fans will allow the use of a couple of different sized ducts...and, if you're approaching the maximum, almost always requires you to use the larger one.

If you're area is subject to potential snow load, you need to take that into account on the type and height of the exhaust vent. It's a good idea to also consider the prevailing wind direction and velocity. You'll need a good damper in the fan (and a second one near the exit isn't a bad idea, either) to prevent a convective loop and have other issues related to efficiency and room comfort.

 

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[Erico]

Mr. Stinky can't be that bad. Just vent it in the yard.

99% or the battle is moisture. That's the most important issue. I wouldn't want the long run to affect the ability of the fan expelling moisture.

Blame the other 1% on the dog.