Using an old boiler flue for an extractor hood

[Johnsmith]

Hello. We removed our boiler from under a chimney breast and are now going to remove the whole of the chimney breast as well and fit an extractor hood. I'd like to use the existing flue that was being used by the boiler to connect an extractor fan (so that cooking smells go up the same route). Does anyone know if this is possible? Will it need to be lined to stop the cooking smells making their way up the upper rooms (where the chimney breasts will still be?) and will the fact that any odours will have to go up 2 storeys affect the efficiency of the extractor? Be grateful for any views. Thanks.

MOD

moved

 

[mapj1]

This should be OK, so long as the chimney is not used for anything else, and was in good order (no leaks) when the boiler used it
But, beware of soot dropping down and damaging the fan mechanism, - you will probable need a stainless steel closure plate, with a hole in it for the fan outlet. Consider how it can be taken apart for repair if a lot of soot or a birds nest drops down it.

 

[Johnsmith]

thanks. just had another thought - will a typical extractor have enough power to extract it all the way up through the chimney breast (and two whole floors - as the kitchen is on the lower-ground floor)? I suppose most of these extractor hoods are only used to pushing out smells through a nearby external wall. Might it just turn to condensation half way up and then drip that down? grateful for any views. Thanks, J.

 

[nstreet]

Most 'run of the mill' cooker hoods have a max ducting distance of about 3.5 - 4.0m. You may want to measure the run and get an uprated model. You will almost certainly need to fit a condensation trap of some description, otherwise you may end up with lots of black gunge all over your nice hood and cooker.

 

[Johnsmith]

Thanks - sounds like good advice. The run will be way more than 5meters (probably double tht at least). Any idea who might sell an extractor with a bit more power, and the condenation trap you mentioned? Cheers, J.

 

[mapj1]

trap could be as simple as a chimney with a hat inside the bigger chimney - dont get too hung up on length - the chimney will be wider than the ducting would have been - resistance to air flow goes approx as square of diameter and linear with length, so twice diameter = 4 times the run length for same fan power roughly. Best to contact the fan makers. technical help dept if they have one.

 

[sandwell]

Would there be a problem with flue condensation, and staining in the upper rooms?
Should the chimney be lined?

 

[mapj1]

Only if you had problems with it before - if it can handle boiler gasses without condensation and leaking, it should be fine for a bit of chip fat and some steam off the veggies..

 

[Bon]

I know this is an old thread, but dug it up whilst doing a search.

I'm thinking of a similar thing to this as we have a chimney breast in our kitchen which is blocked up on both floors. Currently there is a gas hob directly in front of the breast and when we replace our kitchen I would like to put an extractor in. The simplest thing in my mind would be to drill through the chimney breast and let the extractor fire into the breast (providing a smoke test was satisfactory etc..).

Does that sound feasible?

 

[rob wilsher]

Hi
Have tried this-we got rid of our coal fired aga-tapped into the lined chimney flue with a vent axia-USELESS-doesn't work at all-needs a fan at chimney level I guess
Cheers
Rob

 

[Bon]

Seems strange that it wouldn't work. We have 2 Class 1 brick flues in our house. One in the lounge which our gas fire is connected to and the other is in the kitchen and bricked up.

I was of the opinion that the fan would only need to remove the air from the kitchen and into the flue where it would rise up and out of the house naturally, which it is supposed to do as coal fires don't have fans.

Rob, how did you come to the conclusion it was useless?

 

[rob wilsher]

The fan unit is virtually directly above the hob and when we need to switch it on it does not extract a thing and we have to open windows etc.

I had banked on it working particularly as we had a perfect flue-you know, when they put a long balloon down the chimney and pour an insulating mix around it then withdraw the balloon.

It worked great with the aga so I thought it was the ideal use for it. Don't forget that flues become efficient when they are nice and warm from the fire and that might be my problem. Alternatively there could be a blockage in the flue-bird's nest or something-I'll check when I'm up to it-back problems at the moment!

Good luck-it might work for you

Rob-Happy new year

 

[Bon]

Yeah, hope so. As said our flue is a class 1 brick type affair which was designed to move air naturally (but you may have a point about the heat of the air - I suppose as long as it's warmer than the air in the chimney breast it would still rise?)

Will have to drill and exploratory hole and try and get a smoke test done.

It would be worth it to avoid having to duct along the top of the units and around the boiler.