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.