2

My apartment's bathroom fan appears to have been installed to bring a (small) amount of air into the washroom. I've confirmed this with a sheet of paper; pushing it against the grill I can feel a small amount of air being brought into the room.

Is there ever a good reason for it to be installed like this? It's noisy and is almost entirely ineffective at dispelling odours/humidity.

  • 1
    Are you sure it's blowing into the room? I can be hard to tell which direction a low volume of air is blowing just by feeling it. My wife and I disagreed over whether our over-stove fan was blowing air in or out, finally we solved it by lighting and blowing out a candle, then watching which way the smoke drifted. – Johnny Jan 10 '16 at 1:02
  • Yes. It's also exhausting from the room :) I used a lighter and watched which way the flame bent. On the right hand side of the grille the flame bent evenly and consistently towards the grille. On the left hand side, there was a lot of gusting and direction changes, but the flame was consistently pointed away from the grille. – Rich Seviora Jan 10 '16 at 19:33
3

From what you describe it seems unlikely that the vent fan is actually installed to blow backwards. So it would be much more likely that the trouble you are encountering could be one of:

  1. The back draft flapper may be stuck in a shut position. This is a device to close off the vent for air flow trying to come in from the vent pipe. Sometimes they are built right into fan housing where the vent pipe attaches. Other times the flapper will be part of the roof or wall vent where the vent pipe exhausts to the outside. In some cases there could be flappers in both locations.
  2. The vent pipe from the from the fan to the outside may be filled up with dust, dirt or other debris. This could be from years of accumulation or debris blown in or carried in from the outside vent opening.
  3. The vent pipe may be damaged, kinked or flattened. This could happen when workers were careless or for other various reasons due to remolding, adding insulation or re-roofing.

In all three instances there can be blockage of the airflow that the fan is trying to expel from the room. For a significant enough blockage some of the air flow will try to return back into the room around the periphery of the fan blades. This is likely what you are noticing when you held the paper up to the vent grille. It is often the case that a fan trying to blow into a blockage will generate a lot more noise than one that has a free flowing path for the air that the fan is moving.

The fix is going to require careful inspection of the whole vent system from the fan housing all the way through the vent pipe and out to the place where the pipe terminates the roof or wall of the building.

| improve this answer | |
  • I think you're correct. I used a lighter and watched which way the flame bent. On the right hand side of the grille the flame bent evenly and consistently towards the grille. On the left hand side, there was a lot of gusting and direction changes, but the flame was consistently pointed away from the grille. I think that supports your assertion that the noise is generated by turbulence from the change in air direction + vibrations created in the fan due to conflicting forces. – Rich Seviora Jan 10 '16 at 19:32
  • Now hopefully my building management is willing to fix this! One of the joys of living in a wood frame apartment building from 1971. :) – Rich Seviora Jan 10 '16 at 19:34
0

I pulled my fan off from the bathroom ceiling and reached into the exhaust hose. There was 40 years of accumulated dust, like in a dryer filter. The baffle just inside the exhaust vent had about 1/4-1/2 inch of heavy compacted dust on the outside that was weighing it down and the force of the fan was not enough to efficiently lift it. The blockage redirected air back down into the bathroom giving the impression that the fan was either installed incorrectly or was otherwise spinning in the wrong direction. Very noisy too. I cleaned it all out as best I could, put it back together and it vents to the outside good, nice and quiet. (As quiet as any bathroom fan can be expected to be.)

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.