installing an extractor fan within a chimney breast

I am in the process on renovating a house and am planning to install an electric range cooker into the recess of a chimney breast with an extractor fan over it. The chimney in question has been capped, but there is an air vent beneath the cap to allow for air circulation etc. I have had two lots of conflicting advice, one says that I don't need to un-cap the chimney because the air vent should be sufficient and other that due to the amount of steam coming off I do need to have it un-capped. Can anyone give me some advice about which is correct?

Thanks
Newrenovator

Hi, New,
chimneys rarely carry only one flue.
you need to know which flue you are tapping into, and if it starts from the fireplace you are putting your cooker in.
Fire openings have more regs that anything and you need advice.

An air brick does not have the same opening area as a typical extract vent, so the extract rate be restricted with the associated issues to the flue and fan motor.

Also, a flue is not really designed for such damp air, so you may want to confirm what, if any flue lining is present and if this will allow large amounts of moisture to be absorbed

Also check what you’re doing is acceptable; personally I’ve not checked but there have been at least 2 previous posts on the forum which would seem to indicate that tapping into a chimney flue is NOT an acceptable method to meet the air extraction requirements of a kitchen as far as current building regs. are concerned.