Venting bathrooms: how much drop is too much?
For a new home construction (ranch-style with full basement) in mid-Michigan, I am trying to avoid ceiling penetrations as much as possible. Where penetrations are unavoidable, I’d like to keep the potential for air-leakage as low as possible.
If I vent the main-floor bathroom vent fans to the nearby soffit, this provides an unintended thermal bridge and direct path for air-leakage when the fan is not being used. As an alternative, I am considering routing the exhaust duct down through an interior wall, where it would then travel through the floor truss/joist space to the rim board and exit through the exterior wall.
I am thinking the 8′ drop would make it hard for the cold outside air in winter to backfeed into the bathroom.
Would this 8′ drop in height, combined with another 5′ or 10′ of horizontal run, be too much for an energy-efficient fan to overcome when exhausting hot humid air?
If this drop is not too much to overcome, then I am considering an in-line fan positioned remotely in the floor truss space to make it easier to service and/or replace from the basement. Something like Panasonic’s FV-10NLF1 looks appropriate. Is this a workable idea?
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