Blowback on ceiling extractor fan

[larold]

Just bought a new ceiling extractor fan (Manrose) and had it fitted to the ceiling in my new bathroom. It didnt have any blow back flaps so i attached some ducting pipe in the loft. When the fan is turned on, I tested it with a bit of toilet tissue to see if it is extracting sufficiently and the tissue gets pulled up most of the way round the circular outlet but at one small point it seems to blow air downwards instead of sucking up. This seems to be around the point where the power cable goes into the fan from the loft. Not sure if this is just a coincidence or not. Is this normal? Anything I can do to stop it blowing?

 

[stem]

It's not uncommon. Whilst the majority of the air is generally sucked through the blades you can get some leakage out from behind the blades and back into the room through a gap or opening in the casing, or it can be caused by some turbulence around the edges of the blades, but it is usually a very small amount in comparison to the amount of air extracted. It is generally more of a problem with fans at the cheaper end of the market.

If air is blowing out of the flex outlet some silicone sealant or caulk should stop it.

I am assuming that the duct you have connected it to goes to the outside of your house and not just into the loft space. Otherwise you will get condensation in your loft resulting in moisture, mould and rotting timbers.

 

[foxhole]

Is it an inline fan, I just fitted a Manrose and it has non return flaps fitted.?

 

[larold]

Not inline, its a low profile 150mm but it doesnt have flaps

 

[foxhole]

You can fit a non return flap where it exits, cable can access could be sealed with silicon.