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Kitchen Fitting

Installing kitchen extractor fan into old kitchen chimney


Circa 1890 granite bedroom semi detached Cornish Cottage. The house was refurbished by the previous tenants and now comprises a wood burning stove in the living room and sealed chimney in the kitchen. The electic oven/hob now sits in the old chimney alcove but the entrance to the chimney flue above is sealed above. Consequently steam from cooking doesn't have anywhere to go and contributes to the general high humidity and mould growth common in Cornish stone cottages.

There is one chimney stack protruding from the roof, with 2 chimney pipes, so I'm assuming each fireplace has its own flue (or possibly meet further up). What I would like to do is install an extractor fan in the kitchen chimney, either to extract the air up through the chimney (already advised this is a bad idea because of condensation worries) or through a short vertical then horizontal ducting passage to the outside (fireplaces built into external walls).

From general internet research it seems there is a minimum height above the stove of 600 - 700mm for the extractor fan, however the mantel sits only 450mm above the stove (with entrance to the chimney behind it at about 500mm from the stove top). Is it possible to install an extractor fan higher up into the chimney (effectively hidden from view because of the lower reaching mantel)? Or would access and contruction space be too limited? Keen for any and all advice, bit of a head scratcher!

Thanks in anticpation.

Regards, JP

4 Answers from MyBuilder Kitchen Fitters

Best Answer

We come across this sort of thing all the time.

One of the problems tends to be the height of the bottom of the hood above the burning ring, and the minimum beeing specified by the hood and hob manufacturer, and you are meant to go with the greater of the two. It's not just your appliance warranty that is at risk if you don't follow the manufacturer's guidelines, but their distances are specified for safety reasons too.
So what to to where the chimney opening height is not great enough to satisfy the manufacturer's requirements? It isn't usually unthinkably difficult to put in a lintel at a higher point on the chimney allowing the brickwork to be cut-away to a higher level. You'll also have to think about some repair work which could be some plastering etc. The cost of this shouldn't be too bad, but you should factor in some budget for fulfilling your building control obligations, which isn't free. (i.e. notify them of your intent to do structural work and then pay for an inspector to come and see the lintel work that has been carried out before it is plastered over.)

Another issue to be satisfied with is the proximity of the side and rear walls from the burning rings. Some gas hobs require 15cm+ at each side before a vertical surface, and a minimum of 6cm to the rear, and again each hob manufacturer specifies their recommended safe distances. Some hobs therefore won't be suitable for certain chimneys. And definitely don't assume that because you have a 90cm wide gap, you can have a 90cm wide rangemaster, when the chances are you'll only safely be able to install a 600mm wide 4 burner hob. 5 burners tend to need more clearance at the sides.

The other thing to consider is externally venting or recirculating. You can normally do either, and external will depend upon safe access for ducting to the outside. Careful with chimneys though as there can be all sorts of dust and nasties you'd rather avoid in there! Plus really your ducting should run unbroken to the outside which isn't always possible via a chimney. My preference, as long as it is safe to do so, would be to core to the outside every time rather than trying to shove ducting up an old chimney.

Lastly if you're thinking of coring outside, make sure you're satisfied you have fulfilled your obligations as a leaseholder and sought freeholder permissions for cutting through an external wall as some places don't allow it.

Hope some of this helps someone.



Answered 21st Mar 2013

their are regulations on the minimum height of extractors over hobs . and hob manufacturers state the height in their installation guides . electric hobs can have a lower extractor .you can fit a false lid into the chimney with an extractor fitted with a canopy extractor ,if the space is large enough and would advise horizontal ducting as after 3 metres the fan will not push as well and condensation will build up in the ducting .if vertical then condensation will run down.every bend in the ducting will reduce the length of ducting by 1 metre but this will not be a problem if can adapt an expelair fan to do the job but be warned it will eventually get greasy and need cleaning.


Answered 10th Mar 2013

If it's an electric hob there shouldn't really be a height issue, though you may have to accept fitting it lower than recommended will invalidate your warranty.
Other than that I agree with Paul.



Answered 9th Mar 2013

Well, first of all, you need ventilation in all rooms, if you have double glazing, then you need trickle vents. You need good extraction in bathroom and kitchen, venting to the outside. Turning to your cooker extraction, I cannot see any practical reason why extraction should not be lower than normal, it is not going to melt in the radiant heat from the cooker. But it is very simple to install a fan in the chimney using a bit of ingenuity. You will need to get the electrics right. There is in fact no reason why you cannot cure all of the damp problems, ventilation and extraction is a good start, but without seeing the property I cannot advise on other methods, other than to say damp is always curable.


Paul Albright


Answered 6th Mar 2013

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