What is the best cap to use for a thru-wall bathroom exhaust fan install? The ducting is 4" smooth aluminum.
Winters here are brutal. I'm concerned about wind sucking the cap flaps open, letting in cold air. Thanks.
Outside cap for exhaust fan
exhaust
Related Solutions
The Panasonic product you listed supports 4" or 6" round duct, according to the installation manual. 13 feet should not be too far at all, especially if it is a relatively straight run. And to be extra safe, use 6" round duct. The rigid kind, not the cheap flex stuff! The increased size will allow less restricted airflow.
Also, try to avoid using any 90 degree turns. The model you referenced has a side port, which means if you install it between joists you should be able to take the duct straight out of the side of the fan and straight through the exterior wall to the vent cap.
In reality, you should be fine with a straight run of 4" rigid duct. But 6" would give you some peace of mind.
Unfortunately the quietness is often determined by the air restriction. Yes a poorly made fan can rattle or the motor can hum or buzz but even the best fans with no hum no rattle no buzz can still make noise if the diameter of the outlet pipe is too small.
This is the problem with installers
https://www.energyvanguard.com/blog/57709/How-to-Install-Flex-Duct-Properly
Flex duct for all its Glory is installed incorrectly 90% of the time if you're going to run a flex duct and leave it all floppy you better run a much bigger duct or just run rigid or install the
Best Answer
I have two bath fans that are the inline style, 1 for each bathroom. one fan is 4" solid duct end to end, the more powerful uses a 6" solid duct end to end.
From the vent side in the bathroom ceiling, there is a butterfly damper that remains closed due to gravity and lifts up when the bath vent is turned on. On the exhaust side, the 4" bath fan has a plastic hooded exhaust cap, while the 6" duct has a plastic louvered cap.
I would say on very windy days, my 4" duct probably opens up, as I can hear my damper lift up and down sometimes.
I also recently installed a new dryer duct, 4" diameter, where I used a heavier gauge exhaust cap which is damper style, with magnets. This cap could probably work for a bath fan, as long as the fan is powerful enough to lift up the damper flap. I used this one.
I would try adding a damper inline and a beefier exhaust cap.