# Efficiency of bathroom ceiling vents **URL:** \ **Category:** Factual Questions\ **Created:** [May 9, 2014, 7:31pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079 "2014-05-09T19:31:49Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [May 10, 2014, 1:06pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/21 "2014-05-10T13:06:43Z")
The fan in our bathroom when we bought this house was one of those noisy old Nutone bastards. When we had the roof reshingled, we found out that it was venting into the attic; not a good idea in the PNW, where moisture is an issue. So we had it connected to a roof vent. Still, I noticed that it was doing a poor job of removing moisture, as it was a cheap POS. I had it replaced with a [Panasonic low-sone fan](http://www.panasonic.com/business/building-products/ventilation-systems/) with a higher cfm rating, and it’s made a big difference. They’re not cheap, but they’re very efficient and quiet. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [May 12, 2014, 12:13pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/22 "2014-05-12T12:13:46Z")
> [@Reply](#): > > If people use them for odor control, doesn’t that mean the fan is sucking up all the poop particles from the toilet bowl and spreading them all over the bathroom? No, because they take air from the bathroom and exhaust it outdoors. ---
**Author:** ![Fotheringay-Phipps](https://avatars.discourse-cdn.com/v4/letter/f/d9b06d/32.png) [@Fotheringay-Phipps](https://boards.straightdope.com/u/Fotheringay-Phipps)\ **Post date:** [May 12, 2014, 1:32pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/23 "2014-05-12T13:32:16Z")
Here’s a related question: how “efficient” are these fans in undermining your insulation? Meaning, suppose it’s summer/winter and you’re running your ac/heat, and you leave the bathroom fans on for a while. How much have you added to your ac/heating costs by sucking out the cooled/heated air and (at some point) and by changing the relative air pressure increased the amount of hot/cold air from outside that comes in? ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [May 12, 2014, 1:40pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/24 "2014-05-12T13:40:40Z")
> [@Fotheringay-Phipps](#): > > Here’s a related question: how “efficient” are these fans in undermining your insulation? > > Meaning, suppose it’s summer/winter and you’re running your ac/heat, and you leave the bathroom fans on for a while. How much have you added to your ac/heating costs by sucking out the cooled/heated air and (at some point) and by changing the relative air pressure increased the amount of hot/cold air from outside that comes in? Very little. A)Consider how much more you have to heat or cool your house compared to how much you’d have to pay to deal with all the mildew or rotten drywall if you didn’t remove all the excess moisture. B)In summer you’re removing all that excess heat and, more importantly, moisture, which your AC works much harder to deal with, but the fan can get rid of very cheaply. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [May 12, 2014, 1:47pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/25 "2014-05-12T13:47:07Z")
Missed the edit window… I will say that sometimes in winter when it is very cold and dry, I’ll turn the fan off early to let some of the heat and humidity back into the house. Not a full shower’s worth, but if the fan normally runs for, say, 20 minutes after I leave the bathroom, maybe I’ll shut it off after 10 minutes. ---
**Author:** ![campp](https://avatars.discourse-cdn.com/v4/letter/c/c5a1d2/32.png) [@campp](https://boards.straightdope.com/u/campp)\ **Post date:** [May 12, 2014, 2:35pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/26 "2014-05-12T14:35:46Z")
I’m rebuilding a 65 year old bathroom, and will be adding a GOOD fan. Will duct it right to the outside. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [May 13, 2014, 9:15am UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/27 "2014-05-13T09:15:34Z")
> [@rsa](#): > > In my experience in apartments and houses they are cheap pieces of crap that make a lot of noise and hardly move any air out of the bath. Agreed, this is my experience with apartment bathroom fart fans too. I’m also pretty sure that, at least in some buildings, the fans of adjacent bathrooms lead into a common duct that, in turn, goes . . . somewhere. The ducts just above each separate fan, before they join into a common duct, have flap valves in them that (supposedly) prevent air that is sucked out of one bathroom from back-flowing into another bathroom. These tended to be only kinda-sorta functional. And definitely, with noisy fans and shared ducts, whenever anyone went to pee in the night, all the neighbors got a loudly rude awakening. In college, I lived in a rooming house with a basement shower room with adjacent changing area, which had a transom window with a hurricane-strength fan. In the winter (this was in Berkeley, CA), when you stepped out of the showed stall into the changing area, you instantly froze your ass off. I learned to towel myself off (somewhat) with a hand-wrung-out washcloth while still standing in the shower stall so I would at least be semi-dry when I stepped out. I have maintained that habit, in fact, to this day. ---
**Author:** ![Fotheringay-Phipps](https://avatars.discourse-cdn.com/v4/letter/f/d9b06d/32.png) [@Fotheringay-Phipps](https://boards.straightdope.com/u/Fotheringay-Phipps)\ **Post date:** [May 20, 2014, 1:37pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/28 "2014-05-20T13:37:44Z")
> [@Joey\_P](#): > > Very little. > A)Consider how much more you have to heat or cool your house compared to how much you’d have to pay to deal with all the mildew or rotten drywall if you didn’t remove all the excess moisture. > > B)In summer you’re removing all that excess heat and, more importantly, moisture, which your AC works much harder to deal with, but the fan can get rid of very cheaply. Thanks, but these observations do not address the question. You’re just saying that it’s worth running the fan anyway, either to remove moisture or to remove excess shower heat. I’m aware of that. But the situation that raises the issue for me is just letting the fan run on and on for no purpose at all. Like, for example, my kids have a habit of taking a shower and then wandering off and forgetting to turn off the fan long after any moisture-removing has already been accomplished. And the question is how much of a big deal do I need to make about it in hassling them about it. Or perhaps, is it worth my while to get up off the couch and go upstairs and turn it off myself, or should I just leave it running until the next time I happen to pass by that bathroom? And so on. So the question is: > [@](#): > > how “efficient” are these fans in undermining your insulation? > > Meaning, suppose it’s summer/winter and you’re running your ac/heat, and you leave the bathroom fans on for a while. How much have you added to your ac/heating costs by sucking out the cooled/heated air and (at some point) and by changing the relative air pressure increased the amount of hot/cold air from outside that comes in? ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [May 20, 2014, 2:56pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/29 "2014-05-20T14:56:02Z")
there are timer switches for this. they fit in the space of a single wall switch. spring powered timer for maybe 30 minutes. can last many decades. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [May 20, 2014, 3:00pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/30 "2014-05-20T15:00:30Z")
> [@Fotheringay-Phipps](#): > > But the situation that raises the issue for me is just letting the fan run on and on for no purpose at all. Like, for example, my kids have a habit of taking a shower and then wandering off and forgetting to turn off the fan long after any moisture-removing has already been accomplished. And the question is how much of a big deal do I need to make about it in hassling them about it. Or perhaps, is it worth my while to get up off the couch and go upstairs and turn it off myself, or should I just leave it running until the next time I happen to pass by that bathroom? And so on. Install a timer. I see johnpost said the same thing. I put one in because my (ex)wife would leave it on and go to work, letting the fan run all day long. This way it could only run, for at the most, an hour after she got out of the shower. ---
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [May 21, 2014, 6:05pm UTC](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079/31 "2014-05-21T18:05:00Z")
> [@campp](#): > > I’m rebuilding a 65 year old bathroom, and will be adding a GOOD fan. > > Will duct it right to the outside. You won’t regret it. I had a cheap fan that blew into my attic. The mold and mildew took over and I had to remodel my bathroom. Now the fan vents through the attic in a new exhaust pipe and to the outside. Best of all, now when I’m sitting on the toilet, I can tell if it’s windy outside. Since I live in Oklahoma, it almost always is. [Previous page](https://boards.straightdope.com/t/efficiency-of-bathroom-ceiling-vents/688079.md?page=1)