We have an old central air system that includes an electrostatic filter. So the air gets sucked thru a plastic grid filter, then thru several vertical wires at high voltage, then it passes thru several wide metal ground plates and finally thru the air-conditioning system. Every 3 months or so I check it and remove a thick layer of dust like you would on a dryer machine filter. The unit is old and antiquated but seems to do the job.