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Fan-tastic Bath Venting Tips

Bath, Construction How-To, Projects, Remodeling March 22, 2017 Sonia

Pro Tip: Make sure you dry-fit and install the pipe to the exterior vent hood prior to installing screws or tape. You may want to attach the hood to the pipe from the exterior and then slide it into the house wall.

If the duct pipe will run through non-conditioned spaces (crawlspaces and attics), make sure to install an insulation sleeve over it to prevent the moist air from freezing inside the pipe.

Use a hole saw to cut passage for the duct.

A bathroom fan MUST be vented to the exterior of the building to avoid moisture-related issues.

This is often completed with a wall, soffit or roof cap. When possible, I choose to vent my fans out an exterior wall through a backdraft-protected exterior hood.

Pro Tip: On installations with beveled clapboard or shingle siding I often cut the siding back and install a PVC backerboard to the house. I flash this board and pre-drill a hole through it to allow the vent hood to sit flush to the board, thus preventing large gaps.

Attach the mounting plate for the vent hood. Then install the vent hood and seal it to the house exterior.

Fan Noise

When selecting a vent fan, consider how much noise they make. Bathroom exhaust fans measure noise in sones.

Rather than a 4-6 sone bathroom fan, look for one that’s close to or at a 1.5 sone rating—a much quieter fan. You may have to put up with some noise for a more powerful fan, depending on the fan’s size and pipe run layout.

The vent duct shown runs along the wall to a corner of the home.

Most fan labels have Home Ventilating Institute (HVI) ratings so you can compare noise and energy efficiency. Choose the quietest, most energy-efficient fan that will do the job for you.

There are many quality brands: Nutone, Panasonic, Ventech, and Broan. I suggest choosing a fan with a ball-bearing motor for quality and longevity.

Fan Controls

It’s recommended that a bath fan run not only during but for 20 minutes after using the shower—and with the bathroom door closed.

Many people still use an on/off switch for their shower fan. There are two obvious problems with this type of switch. Either people turn the fan off after showering, which leaves a lot of moisture in the air, or they forget and leave the fan on, possibly for hours. I have two daughters who would sometimes leave the fan on all day until I found it running when I came home after work. That’s a lot of heat or AC expelled from the house during the day! As a result I installed a fan timer that has a humidity sensor so it will turn on automatically if they forget or if the room’s humidity is too high.