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.
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.
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 Thursday, December 3, 2015 at 9:09:49 PM UTC, Michael Chare wrote:
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 ...
On Thursday, 3 December 2015 21:09:49 UTC, Michael Chare wrote:
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
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.)
On Tuesday, December 8, 2015 at 9:40:32 PM UTC, Vir Campestris wrote:
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 ...
On Tuesday, 8 December 2015 20:27:04 UTC+1, ARW wrote:
That is clearly true.
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.
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