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They're supposed to be used with a charcoal filter as well as the usual metal filter. They're mostly to trap odors, doubt they do much for air quality.

Many people in the US don't even realize their stove vent is just a filter. They look almost identical to outward venting hoods. Which means the filter medium is never replaced after it fills up with oils either.

> If this bit of context was clear from the get go it would have been a lot easier for those from EUR where we would expect vents outside the apartment to be the norm. ( Not speaking for all EUR, so there may be places this is not the norm )

It is the norm in newer buildings, but there are plenty of older houses or flats blocks in the EU that don’t have a good ventilation system. It’s similarly expensive same in the UK and I cannot say about Norway and Switzerland, but I would think that it is not better in the other non-EU bits of Europe.

Recirculating filters are commonplace in Germany, as well. Unfortunately.

Sadly recirculating vents are the new norm because of energy conservation rules.