I've lived in this house for 20 years. The bathrooms (3) all have switches for fans, but the two upstairs ones do nothing when you flip the switch. Recently, while doing other work, we discovered that there are fans in place and a wire just sitting there not plugged in. On plugging each of them in, we discovered that when you flip the wall switch, you hear a fan sound and it appears to be working.

So why weren't they plugged in? Why did the previous people disconnect them? There are vents in the outside walls in roughly the right places, but perhaps the disconnected fan units in the bathrooms are not connected by any kind of venting or ducting to those outside vents. How can we tell? Is there something we could release into the air in the bathroom and watch for outside? If we go up into the attic crawlspace, what should we look for? If they aren't ducted, what are the consequences of using them - say in a -20C winter when someone is having a hot shower?

  • there were making too much noise for them i suppose. I cant think of anything to check other than put your hand on the outlet and feel if the air is cumming out(or a ligher, if it bends away from the vent its pumping out- which is good, the air should blow it out) You can also apply the lighter near(10-15cm away) the fan; inside the bathroom- and see if the flame bends towards the fan- if its not sucking the flame will bounce back and forwards because of air distortions...meaning the air is not going out.
    – Piotr Kula
    Aug 23, 2011 at 21:27
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    The vents on the outside should have louver(s) (to prevent pests entering the home). So turn on the fan, and go see if the louver(s) are in the open position (which they should be when the fan is running). If they are not open it means the fans are not hooked up, or the fans are not strong enough, or the louvers are stuck.
    – Tester101
    Aug 24, 2011 at 13:09

1 Answer 1


You can tell if they are ducted by looking. Go in the attic and see if they are connected to duct work that goes to the outside.

If not, don't use them as you'll be pumping humid air into your attic space which will lead to either mold and/or water damage.

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    Isn't the hot humid air going to end up in the attic anyway? I would think the fan would just determine how quickly that air got up there, but not running it isn't going to make a path upwards any less attractive to hot air. Aug 23, 2011 at 21:17
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    @Steve Jackson - there should be a vapor barrier on the room side of the insulation in the ceiling that would help to prevent moisture from migrating into the attic, so most of it will mix with the air in the rest of the house (and potentially condense on windows, etc. in certain conditions). Although not great, this is still much better than pumping moist air into a cool or cold attic where it will instantly condense and eventually wreak havoc via mold or rot. As DA01 says, if you can access the length of the duct, a visual inspection should tell you if it is connected.
    – TomG
    Aug 24, 2011 at 11:38
  • Well, hopefully there's a window in the bath that can be opened. If not, yea, you're still pumping a lot of moisture into the house be it in the bath or in the attic. A working vent is definitely the goal here.
    – DA01
    Aug 24, 2011 at 14:33
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    Finally got into the attic and yes indeed, they are not connected. I guess we have a project if we want to use them :-) Oct 2, 2011 at 21:41

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