Just changed the Blue Air purifier filters in the apartment. Above photo shows 3 filters: leftmost is the new filter, the other two are filters from the last year (they are replaced every 6 months).
Filter for the smaller machines (e.g. for bedrooms).
I never open the windows - but there is circulation since the seals on the doors and windows aren't the best. So, I imagine one would have to change the filter every 3 months or so if windows / balcony doors are regularly opened for extended periods of time.
Hmmm... maybe I should change the filters every 4-5 months rather than 6.
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