Kitchen Hood Extractor 100mm or 150mm Core

Hi

Just thinking about what extractor we need for new kitchen in new extension - I see that most of the extractors that Ive been looking at are 150mm

Just spoke to sparky and he said put a 150mm to 100mm reducer on there and cut the hole through the wall at 100mm

Is there any issues with that?? I gather a ridgid pipe is better than the corrugated stuff??

Thanks for any tips