Help! How do I set up an extractor fan to go up a chimney!?

[Richard]

I am about to put a range cooker in where my old boiler was, and as part of this would like to install a 900mm wide extractor hood into the chimney above the new range (the width of the chimney hole being 900mm and depth 370mm). Naturally if I could pump the exhaust gas up the old

100mm boiler flue and out of the chimney, that would seem the most logical solution.

Problem is I cant seem to find info on any manufacturer that supports this configuration. Is the flue too long in such cases or is there some other reason??

Anyway another option I would like to consider is having the motor pulling the gases up the chimney, with the motor set into the top of the chimney, rather than pushing up from the bottom, thereby removing the noise too. Again, cant seem to find any info on this - on the web anyway. Is it possible? Who supplies the gear to do it?

Any advice gratefully received as I really dont want to trunk the flue halfway round the kitchen to find an external wall, when going up the existing flue and chimney seems far more elegant.

Cheers,

Richard.

[Peter Parry]

One problem you will find is that with any significant length of vertical flue you get a lot of oil/water condensate on the flue walls which trickles back into the fan or on to the stove top. You also need to fit a self closing fire damper at the bottom so if there is a fire on the stove it can't propagate up the waste oils on the chimney walls.

[David Hansen]

On 28 Apr 2006 10:54:36 -0700 someone who may be "Richard" wrote this:-

How long is this flue and what sort of terminal is fitted to the top?

I suspect that they all do, but don't want to be burdened with responsibility for the design.

Does the hood have a grease filter? If it does then oil contamination of the flue should be minimal and what is needed is a suitable trap to stop condensate running back down to the mechanism. These can be easily fashioned from standard components, but in essence consist of a tee with the condensate led away to a suitable container or drain. Any book or web page on vertical ducting should explain what is necessary.

[Richard]

Thanks,

Flue is approx 30ft long (bottom to top of a two storey victorian terrace, and the terminal is one of those louvred cylinder types - for a standard gas boiler outlet.

Haven't bought a hood yet, so I guess i could look for one with a grease filter. Is there any manufacturer who make a system desined for such an installation? Will a standard motor be powerful enough to push all the way to the top of the flue do you think?

Thanks for your help.

[justcalledfubar]

We had a similar issue with a terraced house and a bathroom move. We needed to fit a new air extractor fan in the bathroom and for ease of fitting the builder suggested going into chimney breast.

I insisted on either a roof vent or going out through the wall. A friendly corgi registered fitter was in the house recently and his comments after seeing the work and hearing the builders suggestion was unprintable. Basically venting into an existing flue can be dangerous as if there is any leakage from the neighbouring properties flue any fumes could come back into the bathroom. He had seen combi boilers venting into chimney flues before and condemned the installations.

[David Hansen]

On 30 Apr 2006 04:47:14 -0700 someone who may be [e-mail] wrote this:-

You are perhaps mixing up chimneys with flues. Though the latter may be inside the former there is a difference.

[David Hansen]

On 30 Apr 2006 02:18:11 -0700 someone who may be "Richard" wrote this:-

Then water will condense on the underside of the terminal and drip back down. A trap will deal with this.

All the serious suppliers will make such systems for commercial kitchens.

That depends on the type of fan that is fitted. The right sorts of the right size should have no problem. The manufacturers put graphs of this sort of thing in their information.

[justcalledfubar]

Sorry David - perhaps got that wrong. If venting (boiler, extrator whatever) into a chimney would you be OK if you put a flue liner in place?

[justcalledfubar]

Sorry David - what is the difference between a chimney and a flue - don't all operating chinmeys use a flue?

[David Hansen]

On 2 May 2006 14:45:31 -0700 someone who may be [e-mail] wrote this:-

A suitable flue inside a chimney, going directly from the equipment to a suitable terminal, is no different to one outside the chimney as far as exhausting gases.

[David Hansen]

On 2 May 2006 14:45:59 -0700 someone who may be [e-mail] wrote this:-

The terminology is slightly different in different fields, which makes it confusing. However, a flue from an appliance is a tube, usually made of metal, that takes the gases outside without them mixing with other gases.

[nafuk]

A friend did this in a terraced house for his kitchen range. Put a light in the chimeny also. Just used a regular extractor fan (not hood) I think. No problems after two years.

David Hansen wrote: