Bathroom Venting


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Old 07-02-22, 10:27 AM
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Bathroom Venting

Hello All,

I am planning on upgrading my current bathroom vent as it is starting to show some age and doesn't seem to be circulating as much air as it should. The current fan is 110CFM which vents through the roof, but it's not a straight shot. The ducting which is 4", runs upward a foot or so, over/sideways roughly 10 feet, then upward again 5 feet or so through the roof. I know the extra bends alone will reduce the airflow. I am going to purchase a 150CFM fan which would be a closer match to what the bathroom needs, along with using 6" ducting.

I am considering moving the vent through the wall or soffit on the gable end of the house as it would be a fairly straight shot just over 5 feet away The only downside is it would literally be at the corner of the house and no clearance to get to from inside the attic at that point. I could move it inward towards the center of gable end for easier access in the attic, but this would extend the length 5-10 feet and slightly upwards, but still fairly straight. I haven't been able to find much for building codes here in Florida for wall/soffit venting for bathrooms. I thought I heard or read somewhere that you aren't supposed to vent within so many feet of the soffit or any other source of attic ventilation. Does anyone have any input or suggestions to this? Thanks.
 
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Old 07-02-22, 10:36 AM
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I can't quote codes for your specific area but typically you don't vent within 3 feet of anything that could recirculate that air back into the house. If you have soffit intake ventilation, and want to vent out the soffit, you'd need to block off any intake around that exhaust.

International Mechanical code:

506.3.13.2 Termination through an exterior wall. Exhaust outlets shall be permitted to terminate through exterior walls where the smoke, grease, gases, vapors and odors in the discharge from such terminations do not create a public nuisance or a fire hazard. Such terminations shall not be located where protected openings are required by the International Building Code, as amended by the State of Washington. Such terminations shall be located in accordance with Section 506.3.13.3 and shall not be located within 3 feet (914 mm) of any opening in the exterior wall. An opening includes any window (fixed or openable), door, air exhaust or intake opening.
 
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Old 07-02-22, 11:28 AM
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Thanks for the quick response. My 1st thought was to run as straight and close as I could. In the event that there was the 3 foot rule, my 2nd choice was to run it closer to center where I'd have access in the attic to mess with it. The downside to the 2nd option is that it's a little longer of a run and upwards some. Either way I can only imagine it's better then the two 90 turns that it's making now. I've attached a screen shot to give a better example.



 
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Old 07-03-22, 06:01 AM
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You could use your existing exhaust location and make a run a more direct line between fan and vent. You don't need 90's. 45's or any other angle can be used to connect the two points shortening the run and avoiding those flow killing 90's.

Do you have a gable vent on the attic wall in your drawing? That could cross #2 off the list.
 
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Old 07-03-22, 09:06 AM
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My biggest hesitation with using the existing is accessibility and clearance. I can't access it from the attic due to the pitch of the roof. The current vent is only a foot or two away from the outside wall where the rafters meet the joist. The only way to access it is cutting through the bathroom ceiling. I also don't have the clearance to make a straight shot, again because of the limited space due to the rafters/joist. The reason the current duct work has the two 90 bends in it is to get it away from the joist/rafter intersection

As far as gable vents, I don't have any at this time. It's on the back burner so to speak. I'd like to look into cooling the attic at some point since it gets so hot up there, but not a priority at this point. If I end up venting through the wall towards the center of the gable end, I think I can install it low enough to give me the 3' of clearance if I decide to add one later on.
 
 

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