How to Choose a Bathroom Exhaust Fan | Ask This Old House

Ask This Old House master electrician Heath Eastman discusses some new technology for bathroom vent fans.

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Skill Level: Expert

Shopping List:
Flexible insulated bath vent [https://amzn.to/2XGTx2o]
Bath fan register [https://amzn.to/2XHNHxF]
Bath fan [https://amzn.to/2z7qw5V]
Control switch [https://amzn.to/2RKuGXT]

Steps for Choosing a Bathroom Exhaust Fan:
1. Bath fans help move air out of the bathroom to outdoors, in the process removing both odors and more importantly humidity. The fan should be on anytime somebody takes a bath or shower because when you have humidity building up in a bathroom, you invite mold and mildew to form.
2. Heath prefers using a 4-inch insulated flexible venting both to cut down on noise and to prevent condensation.
3. Heath emphasizes that bathrooms cannot vent into an attic. All that humidity will get trapped in the attic and cause mold to form. He suggests venting out a side wall whenever possible. If that’s not possible, go through the roof. Do not vent through a soffit.
4. Heath shows that most bath fans have the fan mounted right over the register, but there is an option where the fan is located elsewhere, often an attic or basement and is ducted to both the bathroom register and the vent to outside. He likes these because they allow for longer duct runs and can allow for proper venting where it might not always be the path of least resistance.
5. Heath also underscores the importance of actually operating the fan when needed and for the appropriate length of time, which can be controlled by timers.
a. The most basic form of control is a simple on/off switch, but that requires you to turn off the fan when you leave the room and it’s really better to run the fan for at least 30-40 minutes after a shower.
b. A decade or so ago, Heath would’ve used a rotary timer switch, which needs to be dialed when you enter the bathroom, and when the time runs out, the fan shuts off.
c. Nowadays, there are digital timers that do the same thing and look a little nicer, but you still have to turn them on to start them.
d. There are also humidistat switches that can go into the wall and can automatically turn on the fan when the humidity reaches a certain point and then turn it off when it dips below that point.
6. There are even newer fans that require constant power at the fan and use a switch leg for more control. It can be set to always be on at a low speed to keep air moving in a home.

Resources:
Heath recommends using an insulated flexible duct for venting bath fans both to eliminate condensation and noise, which are available at home centers. He prefers terminating these vents on a sidewall or through the roof, never into an attic or into a soffit.

Heath showed a bath fan that can be mounted away from a bathroom to help with venting and noise. In this case, the one he showed was manufactured by Fantech [https://amzn.to/2REYgh9] (https://www.fantech.net).

Heath showed options for controlling a fan that included digital timers and humidistats. These are sold at home centers and electrical supply houses.

He also showed a fan that could take modules to control the fan by timer, humidity, or motion. This fan is manufactured by Panasonic [https://amzn.to/2VAwrYC] (https://na.panasonic.com).

Expert assistance with this segment was provided by Eaton and Eastman Electric (http://www.eatonandeastmanelectric.com/).

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How to Choose a Bathroom Exhaust Fan | Ask This Old House
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