Extractor fan advice

[u0362565]

Hi all,

My flat's kitchen has an integrated extractor hood currently setup as a recirculator. Above this on the ceiling but slightly offset from the extractor hood is an axial fan connected to ducting to exterior wall via about 3-4m of ducting with 2 90 degree bends. I'm thinking of changing the setup either to just replace the ceiling axial fan for a centrifugal and leave the hood extractor as is to remove smells. Or I could take out the axial ceiling fan completely and connect the hood extractor straight to the ceiling ducting. One downside to this is that the ducting from the hood to the ceiling will be visible above the kitchen cupboards and as I say it will have to bend a little to account for the offset of the hood outlet and the ceiling duct entry. The second issue is that the initial vertical duct section will be 80cm or so before turning 90 degrees, is this an issue?

It's currently a bit of a mixed setup and seems a shame not to make the hood extract if the ducting is there! Would appreciate any advice on this.

 

[Richard Burns]

I would check the instructions for the cooker hood as attempting to extract via 5-6m of ducting with 3 bends in it may be more than the hood is designed to cope with.
It is almost certainly more than the existing fan is designed to manage.

If things seem OK then it is up to you on the consideration of the decor and what you are prepared to accept.
Ducting can be boxed in if required.
The extract flow rate for a cooker hood above a hob should be at least 30 l/s for new dwellings according to the current building regulations.

 

[u0362565]

Hi Richard,

Yes i'm not sure how powerful it is i can't find a user manual for the hood online anywhere. Its a Blanco Be 01/r and has 16W output, 3 speed settings. Even from that though i probably can't easily estimate how effective or not it will be without trying it. I can't see that there would be much difference between the hoods performance and a new ceiling mounted centrifugal as they're both working on same principal, the only benefit of ceiling mounted fan would be that it doesn't have that extra 80cm of vertical duct that the hood would have to the ceiling.. The axial fan definitely needs to go!

An added complication that might undo any efforts is that the duct out the rear wall has a sort of cowl but its basically almost open to the elements so there's probably more air being forced in than out and the prevailing wind comes from that way, no easy way to access that from 3 floors up to change it to a 90 degree down facing cowl!

 

[Richard Burns]

16W is a very low power fan, cooker hoods are more normally in the 160W range.
Use flexible ducting from the hood to the fixed ducting and see how it goes.
Fit an inline backdraught shutter to stop the air coming in from outside.

 

[u0362565]

Sorry just checked its a 130W motor and says 210W total-assume thats total power consumption, don't know where i got 16W from! I'll see if i can find some semi rigid aluminium ducting, that would look the best and find a way to attach it to the ceiling duct and if possible get a non-return valve. Thanks again.