We recently had to completely replace our air conditioner/heat pump. The technician recommended we get rid of the cheap paper filter that came with it and replace it with a Filtrete filter. At first we wondered if it was worth the expense, but this filter traps more dirt and gunk than I could have thought possible - and we had been breathing all of that in when we used the old filter.

We now check it regularly and replace it every 3 months as recommended and I believe the air in our home has never been cleaner.