I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.


--
Michael Chare
duct in the

On 03/12/2015 21:09, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.



Would it be possible to run a 150mm circular duct? If not the whole way,
just the majority of it until you get to the soffit?

--
Dazza

On 03/12/2015 21:09, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.


I'd have said that 3 metres would be fine. Mine is about 2, with no
obvious problem. Probably less "resistance" if you use the rectangular
PVC duct rather than the flexible corrugated aluminium duct throughout.

On 03/12/2015 21:31, gremlin_95 wrote:
On 03/12/2015 21:09, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.



Would it be possible to run a 150mm circular duct? If not the whole way,
just the majority of it until you get to the soffit?

Quite possibly. I just thought that a rectangular duct would lie on the
rafters more easily. I need to make a proper inspection as the roof is
at a shallow angle and getting to the edge is difficult.


--
Michael Chare

On 03/12/15 21:09, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.



3m is unlikely to be a problem.

On 03/12/15 21:33, newshound wrote:
On 03/12/2015 21:09, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.


I'd have said that 3 metres would be fine. Mine is about 2, with no
obvious problem. Probably less "resistance" if you use the rectangular
PVC duct rather than the flexible corrugated aluminium duct throughout.

+1 - use round or rectangular solid duct as far as possible. May need
some 100x50 flexi to go over the wall plate under the eaves - but then
it is at least a short bit.

On 03/12/2015 22:06, Michael Chare wrote:
On 03/12/2015 21:31, gremlin_95 wrote:
On 03/12/2015 21:09, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.



Would it be possible to run a 150mm circular duct? If not the whole way,
just the majority of it until you get to the soffit?

Quite possibly. I just thought that a rectangular duct would lie on the
rafters more easily. I need to make a proper inspection as the roof is
at a shallow angle and getting to the edge is difficult.



Yep, shouldn't be a problem. As said, solid ducting is much preferred to
flexible stuff.

--
Dazza

On Thursday, December 3, 2015 at 9:09:49 PM UTC, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.


--
Michael Chare
duct in the

We have about 3m of 125mm duct, 2 gravity flaps in the 1m vertical bit, changing to rectangular to output through the soffit, etc.
No problems. Just avoid the flexible stuff like the plague !
Also, of course it totally depends on the power and pressure producing abilities (centrifugal / axial etc.) of the fan ...
Simon.

On Thursday, December 3, 2015 at 10:33:42 PM UTC, sm_jamieson wrote:
On Thursday, December 3, 2015 at 9:09:49 PM UTC, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.


--
Michael Chare
duct in the

We have about 3m of 125mm duct, 2 gravity flaps in the 1m vertical bit, changing to rectangular to output through the soffit, etc.
No problems. Just avoid the flexible stuff like the plague !
Also, of course it totally depends on the power and pressure producing abilities (centrifugal / axial etc.) of the fan ...
Simon.

Use the recommended diameter ducting and as said before avoid the flexible stuff as it plays merry hell with the performance, as will an excess of bends.

"Michael Chare" wrote in message
...
On 03/12/2015 21:31, gremlin_95 wrote:
On 03/12/2015 21:09, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.



Would it be possible to run a 150mm circular duct? If not the whole way,
just the majority of it until you get to the soffit?

Quite possibly. I just thought that a rectangular duct would lie on the
rafters more easily. I need to make a proper inspection as the roof is at
a shallow angle and getting to the edge is difficult.


The duct needs to slope slightly so that any condensation in the duct falls
away from the house.

You may also need to consider insulating the ducting to prevent condensation
forming on the outside of the duct.

But 3m is fine for most rigid ducts.

--
Adam

On Sunday, December 6, 2015 at 3:07:59 PM UTC, ARW wrote:
"Michael Chare" wrote in message
...
On 03/12/2015 21:31, gremlin_95 wrote:
On 03/12/2015 21:09, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.



Would it be possible to run a 150mm circular duct? If not the whole way,
just the majority of it until you get to the soffit?

Quite possibly. I just thought that a rectangular duct would lie on the
rafters more easily. I need to make a proper inspection as the roof is at
a shallow angle and getting to the edge is difficult.


The duct needs to slope slightly so that any condensation in the duct falls
away from the house.

You may also need to consider insulating the ducting to prevent condensation
forming on the outside of the duct.

But 3m is fine for most rigid ducts.

--
Adam

Ah yes, the thing that is annoying me is did I slope the duct - I just cannot remember. Surely I must have done. Anyway, no Legionnaires disease yet !
Simon.

"sm_jamieson" wrote in message
...
On Sunday, December 6, 2015 at 3:07:59 PM UTC, ARW wrote:
"Michael Chare" wrote in message
...
On 03/12/2015 21:31, gremlin_95 wrote:
On 03/12/2015 21:09, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction
to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct
in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.



Would it be possible to run a 150mm circular duct? If not the whole
way,
just the majority of it until you get to the soffit?

Quite possibly. I just thought that a rectangular duct would lie on the
rafters more easily. I need to make a proper inspection as the roof is
at
a shallow angle and getting to the edge is difficult.


The duct needs to slope slightly so that any condensation in the duct
falls
away from the house.

You may also need to consider insulating the ducting to prevent
condensation
forming on the outside of the duct.

But 3m is fine for most rigid ducts.



Ah yes, the thing that is annoying me is did I slope the duct - I just
cannot remember. Surely I must have done. Anyway, no Legionnaires disease
yet !

It's not Legionnaires disease that is the problem but condensate dripping
back into the cooker hood. Or you can blame the slopes:-)


--
Adam

On Thursday, 3 December 2015 21:09:49 UTC, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.


--
Michael Chare
duct in the

You will also need to let air into the kitchen to replace that extracted.

Be specially careful if you have any heating appliances with flues, you could suck poison gases into the house when the kitchen extractor is running

"harry" wrote in message
...
On Thursday, 3 December 2015 21:09:49 UTC, Michael Chare wrote:
I would like to change a cooker hood from recirculation to extraction to
outside. The hood is mounted on an internal wall, however as the
property is a bungalow it may be possible to run a rectangular duct in
the attic and exit via a soffit.

The duct length would be about 3 metres. Is this practical?

I have looked at a Neff installation manual but it does not specify a
maximum length. Just states the obvious that shorter, straighter and
larger is better.


--
Michael Chare
duct in the

You will also need to let air into the kitchen to replace that extracted.

Be specially careful if you have any heating appliances with flues, you
could suck poison gases into the house when the kitchen extractor is
running



Actually you could not be more incorrect.

--
Adam

On Tuesday, December 8, 2015 at 9:40:32 PM UTC, Vir Campestris wrote:
On 08/12/2015 19:26, ARW wrote:
"harry" wrote in message
Be specially careful if you have any heating appliances with flues,
you could suck poison gases into the house when the kitchen extractor
is running

Actually you could not be more incorrect.

I've become more familiar that I'd like with the HETAS regs recently -
and this is mentioned as a potential problem.

(In practice as we have so many draughts, and the flue draws really well
so it's not an issue.)

Andy

We smelt an ashy or coal-like smell with the cooker hood running the other day. I shut the underfloor vent to the Baxi Burnall grate, and the smell went away. The hood must have been drawing air through the vent and the ashes and into the room ...
Simon.

On Tuesday, 8 December 2015 20:27:04 UTC+1, ARW wrote:
"harry" wrote in message
...

You will also need to let air into the kitchen to replace that
extracted.

That is clearly true.

Be specially careful if you have any heating appliances with flues, you
could suck poison gases into the house when the kitchen extractor is
running

Actually you could not be more incorrect.

I hate to say this, but I think harry may be half-right this time.

Clearly something like a boiler with a balanced flue will be fine -
but anything connected to an *un*-balanced flue (in other words, an
ordinary chimney) will need adequate ventilation to ensure that
the extractor doesn't suck the flue gases into the house.