Re: Bath fan vent - roof vent w/ 2' run or wall vent w/ 20' run?
Posted by ChuckW on August 17, 2001 at 12:46:45:
In response to Re: Bath fan vent - roof vent w/ 2' run or wall vent w/ 20' run?
: Hello,

: I am in the process of remodeling our second floor bath and am wondering which way is best to run the duct for the bath fan. I have two options, as my first choice - a soffit vent - is not available b/c, alas, there are no soffits. I can either put a 90 degree elbow right off the exhaust hole of the fan and run it straight up for 2 feet through a roof vent, or I can run it horizontally as I have seen most often recommended down the length of the gabled roof to the rear of the house, which would be about a 20' run. It seems to me that the roof vent would be preferable, with the only drawback of the possibility of (1) leaks from outside, and/or (2) condensation dripping back into the fan due to the vertial pipe run.

: I figure insulating the vent pipe will help alleviate if not eliminate the condensation issue. Thus, I'm really only concerned about installing the roof vent, assuming this is the best way to go.

: What is the best way to go about installing a roof vent for the 4 inch vent pipe?? As I've never cut a hole in my roof I'd be interested in any advice on the best way to go about it. I assume I'd use my jigsaw, but I'm wondering if the 4 inch hole should be oriented with the pitch of the roof OR should it be oriented straight up and down (meaning the actual hole in the roof would be oval in shape) so that the vent sits upright on the sloped roof. I would think it would be the former, but am not exactly sure how to go about this. Any comments or help would be greatly appreciated. Thanks in advance.

: Mark in KC
The shape of the hole doesn't matter, it can even be square. The roof vent flashing will cover the hole and seal to the vent pipe. I also was paranoid about cutting holes in my roof, but after 3 - its no big deal. Just make sure the vent flashing is water tight to your roof material.

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