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I would like to install a fan in our bathroom which currently has none. However, I'm very confused regarding the best approach for this.

Above the bathroom is an attic space. I have read that venting out the gable side of the house is preferable to soffit vents or roof vents. This makes sense to me because it avoids roof penetration and venting out the soffit may allow the hot, moist air to re-enter the attic through the neighboring soffit vents. In addition, bends in the vent duct are discourage because they reduce airflow.

However, all ceiling mounted fans I've seen sit between the joists and the vent outlet runs parallel to the ceiling joists (toward the soffits). In order to get to the gable end, I would need to put two bends in the duct -- one to turn up and above the joists, then another to turn and head toward the gable end. From where the fan will be, it is no more than 10 feet to the gable end of the house.

Should I make these two bends and vent out the gable end?

Should I build a box for the fan, recess it above the joists so the vent outlet is in the direction of the gable end of the house?

Should I forget the ceiling vent and use a wall mounted vent? (If I do this, I believe I will need to still vent out under the eaves which will present the same issue with the soffit vents, no)?

Or is there another option I'm not aware of?

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I'd recommend venting out the gable. Run a rigid vent from the gable wall to a point near your install, and use a 2' piece of flex duct to connect the fan to the rigid vent. The flex duct makes the bends easy (don't kink it) and allows the fan to be repaired from below in the future. For that length, I don't think you need to worry.

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  • Is it better to use a short piece of flex duct, or two of those adjustable elbows? The adjustable elbows would allow better air flow, correct?
    – DCNYAM
    Nov 7, 2011 at 13:39
  • @NYSystemsAnalyst Adjustable elbows allow better airflow. Flex duct allows you to replace/repair fan from below without ripping open the ceiling. For that short of a distance, I'd go for the flex duct.
    – BMitch ♦
    Nov 7, 2011 at 14:27
  • I ended up purchasing an inline fan from Panasonic. This allowed me to mount the fan on top of the ceiling joists pointing toward the gable. I then just needed one bend to come up and over the joists into the fan, then a straight line out to the gable end.
    – DCNYAM
    Nov 24, 2011 at 14:44
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The "best" approach is to take the shortest straight path to get the exhaust air out of your house. Generally that's via a roof vent. Check out this answer for a little more info.

Your plan A, two bends and out the gable end is fine as an alternative. 10 feet is not a very long way for a bathroom exhaust vent. If possible, use a rigid vent to avoid sagging and possible condensation build-up.

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