Air purifiers

Air purifiers were a small row next to dehumidifiers and fans. Two different machines got filed there: a fan pulling air through a filter, and an ionizer that charges particles so they stick to a plate or to the nearest wall.

A mechanical HEPA filter catches fine dust if the air actually goes through the paper. Gaps around a bent filter pass dirty air and the rating no longer describes the room. CADR, the clean-air delivery rate used on many U.S. boxes, is measured separately for smoke, dust, and pollen. A high number on pollen with a weak number on smoke is a real pattern. Match the CADR to the room you close the door on, not to the whole house, unless the unit is built as a whole-house media cabinet on the furnace.

An ionizer can drop dust out of the air and it can also leave a dark line on the wall near the machine. Ozone is the byproduct to read the label for. A purifier does not add oxygen and it does not stand in for a bath fan that should be dumping steam outside.