Bathroom Fan Installation Tips

Bathroom Fan Installation Tips

We are in the middle of building a new bathroom in a friend’s basement. It is a small space that will house a sink, shower and a toilet.  Since there is no window to provide ventilation, the Uniform Building Code (UBC) — and common sense — suggest that a fan be installed. My friend picked the Panasonic FV-08VQL5, a very quiet model that includes a fluorescent light. It is plenty powerful for that small space, and even includes a night light.

I prefer solid sheetmetal ducting over the flexible kind. Sheetmetal is long-lasting and, most importantly, it allows for unobstructed air flow and thus best performance. Flexible ducts contain coiled metal wires to maintain their shape. It gives ducts a ‘ribbed’ appearance, but those same ribs also obstruct air flow. Sure, rigid ducting takes a bit longer to install and costs a few dollars more, but so what? I’d rather do it right the first time. A contractor-friend of mine has this note following the signature line on email messages he sends: “A job once done well is done for ever.” (Thoreau

Panasonic bathroom fan housing and rigid duct

A few details to keep in mind:

  • Most fans allow a maximum duct length, depending on the diameter and on how many elbows are used. Check the installation instructions or give the manufacturer a call.
  • Before you start installation, decide where the duct will end. It must be somewhere through an outside wall or roof. I have seen plenty of installations where the duct was vented into an attic or crawlspace, but please resist the temptation to do so. You do not want moisture accumulating in such areas.
  • The outlet must be at least 3 feet way from any window, door, or skylight, and any property line.
  • When you fasten the duct to the fan, use foil adhesive tape only. Screws might interfere with the ‘flapper’ inside the fan that prevents back-draft. At all other joints, install 3 sheetmetal screws in a triangle shape, and wrap the entire joint with foil tape. The duct can be supported with metal or plastic plumber’s tape.
  • It is also a good idea to wrap the duct with insulation and slope it toward the exhaust vent at the exterior wall. That way any condensation that builds up will have a place to go.

Wiring is a breeze. Just make sure you do not accidentally connect the night light to the switch leg. Because my installation will no longer be accessible once the gypboard is installed, I did a dry run to make sure everything worked the way it is supposed to.

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