Electrical Question

Can a kitchen extractor be ducted downwards and towards the outside under a floor?

I have my cooker in a chimney breast on an inside wall. I'd like to add an extractor fan but, due to various obscacles, venting to the outside at ceiling level is looking difficult (and I don't think up the chimney is an option - I am on the ground floor of a 3-storey house)). Would it be feasible to take the ducting from the extractor down under the floor (where I have a large under-floor void) and across to the external wall (about 3 metres) and vent out at ground level?

Is this a possibility?

Thank you in anticipation for your advice (and please don't tell me just to have a recirculating extractor!!)

6 Answers

Best Answer

Hi there, couple of problems, hot air rises so it always going to back venting, any oils will collect at the lowest point causing a pool of grease which will get heavy stress the duct and want to drop downward, I could also see this as a possible source of ignition (FIRE). (Rodents will love this food source)
what about using rectangular trunking and boxing it /clipping to your ceiling wall and extracting. I would look again at venting into the chimney, some sort of vent to stop debris falling back into your outlet would allow the extractor to work,

Answered 3rd Jun 2011

Pro Finishing Services

Member since 12 Jan 2010

What you are proposing sounds fine in theory but how would you hide the vent pipe between the extractor and the floor.Another option for you would be to use charcoal filters,Most new extractors offer this option and as time has passed they are now really quite efficient,hope this helps,

Answered 4th Jun 2011

m w building construction and property maintenance

Member since 28 Sep 2008

hi, you can duct up the chimney as extractor is for getting rid of smells not steam. You may have seen houses with range cookers in chimney breast with extractor above?

Answered 3rd Jun 2011

AJ Plastering & Building Services

Member since 14 Jan 2010

I see no reason why you cannot do this, but you willhave to get an extractor powerfull enoughto cover this distance,you may even deed one inline about halfway to boost it, regards Terry.

Answered 3rd Jun 2011

tm property services

Member since 9 Mar 2011

I would avoid trying to make warm or hot air go down. You also risk water building up water in the pipe from condensation, which i have seen before. If the vapours rise they escape naturally. I have seen extractors vent in chimney's before as long as the upper floors don't use the chimney and it is lined to the top. I'm not sure of the layout but there must a better way, you can get ridged narrow ducting which can run in floor voids. See if you can get some free quotes from my builder which may throw up some different approches. I hope this has been helpful.

Ed Haynes.

Answered 3rd Jun 2011

Edward Haynes domestic electrical installer

Member since 3 Nov 2010

As long as you use foil-based ducting to cope with the heat of cooking fumes, and allow for the draining of any condensate to avoid water traps or damp problems, there's no reason you can't do it. The only thing to be mindful of is where the exhausted vapours are likely to end up. Venting within range of an open window, front door or airbrick will mean the owner of said intake point will benefit from some peculiar odours! Most extract hoods have centrifugal fans, so increased ducting length will not majorly affect performance, but if you're installing a standard fan you need to make sure it's up to the extra pressure. Up the chimney would allow convection to give you trickle venting when the fan's off, but I believe it's against building regs to use chimneys as anything other than a normal flue?

Answered 4th Jun 2011


Member since 7 Nov 2010

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