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Should you always run your bath fan when you shower?

Last week was freezing.  With it being so cold and dry outside, we wondered about the advice we often hear about making sure we run our bath fans during every shower (and let it run 20 minutes after a shower). While some of us have very dry homes (think static electricity and dry scaly skin), others of have pretty cozy homes (relative humidity closer to 30% in winter is pretty nice), while others have water condensing on windows and iced-over window frames causing lots of headache.  So, should everyone follow one rule? Let’s check in with Building Science experts Energy Vanguard, who just published a blog on this topic.

morning-shower-bathroom-condensation.jpg“You may have heard or read somewhere that you should run your bathroom exhaust fan whenever you take a shower and then let it run for a while after you’re done with the shower. Showers increase the humidity in the bathroom. Sometimes it gets high enough to cause condensation to appear on the mirror and other surfaces in the bathroom. And that can result in mold growth. So you should always run your bath fan when you shower. Or so they say.”

morning-shower-winter-temperature-relative-humidity-bathroom.pngThink about this: You take a shower, which increases the humidity in the bathroom. So you turn on the bath fan, using energy to suck out the humid air. Then you use more energy to heat the air that has to be made up by the air exhausted from the bathroom. Then you use more energy to run a humidifier because your indoor air is too dry. Hmmmm. Something doesn’t add up here.

Read more on this topic on the Energy Vanguard Blog.

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