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Bath fans: ceiling-mount or inline?

On my new build currently under construction, I am trying to determine which route to go with the bath fans. I have a 100sqft bath and a 65 sqft bath. The 2 vent locations are either a gable end or straight up through the roof. They will go in a unconditioned vented attic space with r60 blown insulation.

I much prefer the gable, however the closest gable is about a 25' duct run for the fan. I am thinking if I go this route an inline fan may be the better solution, such as one from Fantech.

If I go straight up through the roof, its only about a 5' climb, however the roof is a 3:12 low slope in zone 6.

I am debating between Delta, Fantech, and Panisonic bath fans for ceiling mount, or Fantech for inline. I think I will go with the Seiho SFZC vent cap with a built in damper. This would give me a damper on the fan and the exhaust cap.

I am a little concerned about the 25' run to the gable, but I also do not want to put 2 more holes in the roof. Anyone have any thoughts?

Asked by Jesse Lizer
Posted Feb 5, 2013 11:44 PM ET
Edited Feb 6, 2013 2:09 PM ET


4 Answers

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Have you thought of using an ERV/HRV and running ventilation through the sill box?

Answered by Kristopher Steege-Reimann
Posted Feb 6, 2013 8:45 AM ET


I'm not sure that inline vs ceiling mounted makes a difference, other than the inline fan might be more power per sone of sound heard in the bathrooms. The fan still has to pull the full length of the run.

Two considerations for me when i thought about this were:
1. With an inline fan split to two locations you get air pulled from the bathroom that is not in use. We didn't like that idea, anticipating a cooling effect from airflow, especially while wet just after a shower (if someone turned on the fan in the other bathroom).

2. Definitely preferring a gable end, I figured out the airflow requirements and oversized the duct run (using 6" smooth metal ducting rather than 4" flex ducting). You should be able to figure out, using Manual D calculator tools (perhaps someone has a link?), how large your ducting would need to be over that length to ensure sufficient airflow.


Answered by James Howison
Posted Feb 6, 2013 12:34 PM ET


Kris- an HRV is going into the house, but I do not want to route things that way.

Looking into it more last night, I am leaning most heavily on efficient ceiling units with a dedicated run to the gable for each fan.

Answered by Jesse Lizer
Posted Feb 6, 2013 12:40 PM ET


I do not have any straight numbers, but i can tell you by experience that the panasonic ceiling mounted whisperline fan can work with up to 60-70' of 4" assuming you do not use sharp corners.
It will hinder the flow somewhat, but i am still getting a very decent removal of humid air at that length.
So any fan with the same specs or higher will work more than enough at 25' of length.
and no need to oversize the pipes to 6" at 25' ..

It is more important to have the fan running during the shower/bath than long after,
especially during winter time , wehre u can gauge ur humidity levels so not to have it run too long for anything ...
during summer time you can close the door ( assuming bottom door gap exists ) and leave the fan on much longer

We have it on a 5-15-30-60 timer , a humdistat could be worth it also.

Are you using HRV anywhere else in the house? how tight is your construction ?


Answered by Jin Kazama
Posted Feb 6, 2013 6:02 PM ET

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