Air brick extractor

I am fitting a bathroom extractor fan the bathroom has an existing vent via an outside airbrick if I remove the vent can I put my new 4inch ducting upto the old airbrick or will this restrict the airflow.
Would it be better to cut a hole in the airbrick and put the ducting through it with an outside backdraft shutter.

 

In my opinion it would be better to leave the existing airbrick alone, hire a 4 inch (approx - check measurement) core drill and make a new hole somewhere else.

Use a duct through the entire wall. Outside, use a 'gravity' grille - the type with the flaps which hang down.

Using existing airbricks in my experience causes nothing but bother.

 

And a shroud, otherwise the flaps will clatter in the wind.

 

Indeed
For a fan to be effective, you need to allow an equvalent volume of air into the room.
The airbrick will be perfect for that.

 

It depends whether your house has been built with cavity or solid walls (as many English houses were)
If the alls are solid then completely remove the air brick and use the aperture for your fan ducting and outer draft flap, then make good the space between the duct and what remains of the old brick aperture.

 

But as has been said in previous posts do I need to keep the air brick vent to supply air into the room for the fan to work effectively

 

It depends where it is.

Obviously, right next to the fan would be useless.

 

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