What’s the best way to vent a bathroom fan?
user-1035959
| Posted in General Questions on
I have the option to vent through the gable wall with a long 20 foot run or through the roof with a short (4-6 feet) run. Climate is mixed. Cold winters, hot humid summers. I’ve heard that there’s a good chance of condensation forming in the vent piping and dripping down back into the bathroom if I go through the roof. But isn’t this somewhat less of an issue if I insulate the piping and run the fan a bit longer?
Lastly, is there a bigger energy (heat loss) penalty going through the roof as opposed to the gable wall? There will be a backdraft damper either way.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Jason,
Go to the gable wall. Use pipe that is one size larger than the diameter coming off the fan. Go straight up from the fan to a height that is adequate to allow the 20-foot-long straight run to be sloped downward toward the outside termination. (That way, condensation drips towards the outdoors.) Use rigid galvanized pipe, with the male ends facing the outside termination. If you want, wrap the pipe with insulation.
Support the pipe every 3 feet or so with good quality strapping.
What about if the gable end still has vented soffit under the eaves? Would a higher CFM fan be needed due to the long run or does the larger duct make up for that?
You also want to make sure that any vent cover that is placed on the pipe/duct is placed on the exterior of the duct and not the interior, as condensation will leak between the duct and vent cover if it is placed within the the duct, and then run down your wall. Aluminum duct work is also good to prevent decomposition of the metal.
regardless of location make sure the duct runs down hill to termination and not back to fan.....