Bathroom extractor blowing back

Tomc

Hi. I have installed an ‘Envirovent silent 100’ extractor fan in my en-suite following the previous fan stopped working after 9 months.    It appears to extract in the middle of the fan but blows out air from the sides of it. It’s has a thin plastic flap above the fan to stop draughts coming back down etc when not operating, is this normal? Should it not extract from all sides and not just the middle?
Thanks
T..

Jeepers_Creepers

Yes, the thin flap is for what you say - to prevent down draughts the the fan is off.

Can you tell if it's being blown open properly? If your fan isn't that powerful, and/or if there's a long ducting run, then it might not be strong enough to fully open that flap.

But, are you sure there's air being blown back down? Hard to see how this can happen - the blades can only pull in one direction. It can be misleading - sometimes the feel of the air can deceive you into thinking it's blowing rather than sucking. Test it with a sheet of tissue. 

Finally, it can be the case than in strong gusty weather (like the last couple of days) the air passing through your house will form a negative pressure area in that room, so the fan simply cannot overwhelm the natural downdraught - ergo it blows back down.