Kitchen extractor replacement - duct size

Hi, I'm in the process of replacing my kitchen extractor as my current one is broken. Upon inspection, I noticed that the old extractor is vented externally using 100mm flexible ducting, including the roof vent which is 100mm in diameter. The user manual for my new extractor (Neff model - max extraction rate of 630m3/h) says 150mm or 120mm ducting is "recommended". I will also have at least 2 90 degrees bends in the ducting. Should I bother to upgrade my ducting and roof vent to 120mm (which will be a big job)? I have read that I'll loose extraction performance and I might get unwanted noise if I use a duct that is below recommended but in practice, is this significant? Many thanks in advance for any advice.


  • Hi
    Based on the maximum performance of 630m3/hr using 150mm duct the air velocity will be around 10m/s this increases to around 23m/s using 100mm dia duct, knowing you have a couple of 90 degree bends in the system the result will be a very high reduction in the performance. I would suggest either increasing the size of the duct or change your model to one that requires 100mm dia duct, but will offer a lower maximum performance. The combination of a 100mm dia duct and Extraction Canopy with a 630m3/hr performance is going to be a waste of money. The air velocity noise will be high at 23m/s but the noise from the fan in the unit will be higher.

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