Cooker hood and chimney flue

[mrjoe]

Morning everyone,

I've removed a wall in my 1930s semi to create a kitchen dinner, the removed wall had a chimney running up it which has also been removed as far as the new RSJs (one either side of the chimney,,, a different story!). The idea being to have the new hob on a peninsular where the wall used to be and have the cooker hood hanging down from the RSJs, venting up the chimney.

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I'm a bit concerned about condensation and grease etc in the chimney.

There is a steel liner which runs up for the first metre and a half or so then just brick work.

I'm thinking of dropping a PVC flexible (as the chimney zig-zags at the top) duct down the chimney from the top and putting a suitable weather cover on top. Its about 6m so will need to find a hood that can deal with that.

My concern is that the chimney (outside the duct) will effectively be sealed and not be able to breath. is this a problem?

Does what I'm suggesting sound like the way to go? or should I stop worrying and just attach the hood to the steel pipe?

Thanks for reading,

Joe

 

[stem]

I would not use the metal ducting. Steam laden air being extracted could condense inside the cold metal duct and run down back into the cooker hood. Condensate traps are available, but they can be awkward to fit and need to drain to a suitable discharge point. It's possible, but less likely for condensation to form in a plastic duct. It depends how cold the chimney gets.

There is also the length of the duct to consider. Normally, hoods are connected to a few metres of horizontal ductwork and the fan is designed to cope with this. To overcome the friction / air resistance of a long duct and generate the pressure to lift a column of air vertically for possibly 8 metres will require a fan able to generate considerable pressure. Unfortunately this information is not readily available for most cooker hoods.

As a suggestion, you could look for a hood that you would like to use, but before buying it download the installation manual. Inside you will find a technical helpline number. You could then ring this number and ask if their unit is suitable for the duty you propose.

 

[foxhole]

You need grease filter in any hood unit to prevent it entering the chimney, avoid plastic above an oven due to fire hazard, the extractor fan should be powerfull enough to throw the damp air up the chimney and also keep it dry.
Chimney needs a vented cap to prevent rain entering.
Though chimney is not the best way to vent an oven, ideally should exit to the outside as close as possoble to hood unit.