Any such thing as a powerful recirculating kitchen extractor fan?

[another20]

Hob not in an outside wall - so thinking about recirculating one? Is it a waste of time? Or should we vent directly up on to flat roof - loath to do this as roof is new after years of leaks - don’t want to compromise it.

You can fit a recirculating one to reduce the grease floating around, but you still should have a separate through the wall fan elsewhere to dissipate the humidity outside after cooking.
Opinions vary on how good the recirculating ones are, we made one ourselves with a 2 inch thick stainless steel grease filter, some of the more decorative ones only have a centimetre or so grease filter.

You need to instal a system that's as good as or better than your current one for building regs approval. So if you current one vents out - the next one needs to be vented out too . Doesn't have to be over the hob as long as it's in the same room and vents 60lps.