I am looking to install an extractor fan in a newly created internal
kitchen. The problem I have is that the nearest point to which to extract
(i.e. external wall) is some 4m away.

I will be fitting a 6" extractor as per Building Control instructions. The
ducting, together with the waste from the sink, will run behind a new
partition wall in the adjacent room. I would like to keep this new wall as
close as possible to the existing wall as the room is quite narrow already.

I intend to use a standard wall mounted fan - something like this one:
http://www.screwfix.com/app/sfd/cat/...23262&id=24840).
My question is: will it be OK to run 4" ducting for it along the 4m span?
Can I use something like this:
http://www.screwfix.com/app/sfd/cat/...23473&id=14118 ?
It would make my life much easier as I will only need two flat-to-round
adaptors on either end, and I would lose less of the room. It seem much
harder to find adaptors, etc for the 6" flat one (
http://www.screwfix.com/app/sfd/cat/...23473&id=59769).

Considering that these fan are only designed to work to their full capacity
with straight ducting of 2-3m according to the manufacturer (mine will be a
pretty messy 4-5m), I just thought that I could get away with using smaller
ducting. Is the only drawback the drop in performance, or is there anything
else I need to consider?

I should probably add that I am not too concerned with the performance of
the fan, as it is only there to satisfy the BCO demands, and I will happily
live without the fan altogether (personal choice, I know).

Many thanks in advance for your thoughts.

J.

JoeJoe wrote:
Considering that these fan are only designed to work to their full capacity
with straight ducting of 2-3m according to the manufacturer (mine will be a
pretty messy 4-5m), I just thought that I could get away with using smaller
ducting. Is the only drawback the drop in performance, or is there anything
else I need to consider?

I would have thought the only other problem might be that of
condensation potentially collecting within the ducting; not that that's
not an issue with shorter runs, just that it's likely to be a bit
harder to get a reasonable and consistent fall on the ducting if it's
going to be 5m long.

Changing from round to square cross-section will inevitably clobber the
performance as well, but I expect you're aware of that.

David

JoeJoe wrote:
I am looking to install an extractor fan in a newly created internal
kitchen. The problem I have is that the nearest point to which to extract
(i.e. external wall) is some 4m away.

I will be fitting a 6" extractor as per Building Control instructions. The
ducting, together with the waste from the sink, will run behind a new
partition wall in the adjacent room. I would like to keep this new wall as
close as possible to the existing wall as the room is quite narrow already.

I intend to use a standard wall mounted fan - something like this one:
http://www.screwfix.com/app/sfd/cat/...23262&id=24840).
My question is: will it be OK to run 4" ducting for it along the 4m span?

If you can get hold of the flowrate vs. back pressure curves for the
fan it would be worth calculating its effectiveness in your proposed
setup. Further details, including the method and pressure figures, in
the Domus catalogue at
http://www.domusventilation.com/asse...CatOp05_06.pdf (5MB PDF).

Mathew

"Lobster" wrote in message
...
JoeJoe wrote:
Considering that these fan are only designed to work to their full
capacity with straight ducting of 2-3m according to the manufacturer
(mine will be a pretty messy 4-5m), I just thought that I could get away
with using smaller ducting. Is the only drawback the drop in performance,
or is there anything else I need to consider?

I would have thought the only other problem might be that of condensation
potentially collecting within the ducting; not that that's not an issue
with shorter runs, just that it's likely to be a bit harder to get a
reasonable and consistent fall on the ducting if it's going to be 5m long.

Changing from round to square cross-section will inevitably clobber the
performance as well, but I expect you're aware of that.

David

I thought about condensation, and intend to run the ducting at a slight
angle.

My only ral conen was whether long ducting will have any effect on the motor
of the fan - i.e. will it cause it any damage, will it burn one day, is it
safe?

On Wed, 19 Oct 2005 13:15:30 +0100, "JoeJoe" wrote:


Considering that these fan are only designed to work to their full capacity
with straight ducting of 2-3m according to the manufacturer (mine will be a
pretty messy 4-5m), I just thought that I could get away with using smaller
ducting. Is the only drawback the drop in performance, or is there anything
else I need to consider?

You should use _larger_ ducting in this case.

I should probably add that I am not too concerned with the performance of
the fan, as it is only there to satisfy the BCO demands, and I will happily
live without the fan altogether (personal choice, I know).

The longer the ducting and the smaller the cross section, the more
back pressure you will get and this will reduce the performance of the
fan and it's life expectancy.

M.