How long should the bath fan be running?

13 years ago

DH and I are on different pages when it comes to the bath fan being on and for how long, so I've come to you guys for help.

Should the fan be on the entire time while showering?

Should the fan remain on for a certain amount of time after showering?

Should the fan be on only after showering?

We installed a timer which has been amazing but DH thinks I leave it on to long and I don't think he has it on enough.

Is there a rule of thumb for this?

Thanks!

Featured Answer

lazypup

13 years ago

If the fan is sized correctly it should move enough air to cause a complete air exchange in the entire room 4 times an hour (every 15 minutes).

For best performance it should run long enough to effect one additional air exchange after you leave the bathroom which means it should have a 15 minute delay on break timer, which means the fan will continue to run for 15 minutes after the switch is turned off.

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Comments (8)

Billl
13 years ago
"Is there a rule of thumb for this? "

yes - run it until the moist air is gone. How long that takes is going to depend on the size of your room, the power of the fan, and anything that might obstruct air exchange.

If you run it while showering, you'll keep much of the steam from building up in the first place. From a water management perspective, that is a good thing. If you prefer a steamy shower though, it would be a drawback.
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terezosa / terriks
13 years ago
I normally like a nice, hot steamy shower, except after exercising, so I normally don't run the fan during the shower. We have our fan on a timer, so I set it for 30 minutes after my shower. Seems to be enough time to clear the room of steam.
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ntruro
13 years ago
Minutes x fan cf/m = air displacement. On average, in our household 4 showers are taken per day. The fan timers are set for 30 minutes (10 minute shower time plus an additional 20 minutes run time). The shower fans are rated at 110cf/m.

4 x 30 minutes x 110cf/m = 13,200 cubic feet of air displacement. Even if the fans run at only 80% efficiency, air displacement is still 10,560 cubic feet. That's a lot of conditioned (heated or cooled) air pumped out the roof vents. (If you have a 2,500 sq ft home with 8 foot ceilings, half the air in your house is pumped out daily.)
itltrot
Original Author
13 years ago
I run it for 30 mins. 10-15 min shower and 15-20 min run time after shower.

DH has started running it for 10 mins after shower only.

This last weekend while cleaning the shower, I noticed the first signs of mildew on the caulk above the tub. It wasn't there a couple weeks before and in my mind that is about when DH changed his fan routine.

I'm sure the fan in the bathroom isn't as large as it should be just because nothing seems to have been done right in this house. Which is why I'd rather run it longer than shorter.

Thanks for the information.
PRO
Avanti Tile & Stone / Stonetech
13 years ago
20 minutes............(put it on a timer)
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helenab
13 years ago
I have an additional question -- what if there is an open window in a small bathroom? My husband believes we should not use the fan when the window is open, as the air coming in from the outside is being drawn out.
Billl
13 years ago
Typically, the hot, steamy air rises and the cooler, dry air sinks. That means the moist air goes up and out no matter where the new air is coming from. Of course, a good strong wind will change that equation,but in general, a fan is better at air exchange than a window is.
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How long should the bath fan be running?

lazypup

Comments (8)

Billl

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terezosa / terriks

ntruro

itltrot
Original Author

Avanti Tile & Stone / Stonetech

helenab

Billl

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How long should the bath fan be running?

lazypup

Comments (8)

Billl

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terezosa / terriks

ntruro

itltrotOriginal Author

Avanti Tile & Stone / Stonetech

helenab

Billl

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itltrot
Original Author