I previously owned an air filter that used standard-sized filters, so you could go to the hardware store and get a HEPA furnace filter in that size instead of paying a FORTUNE for the "official" replacement filters. I thought I would do the same on this model, but they wised up and used a completely non-standard filter size, so you have to go through them for the replacement filters (which cost as much as the unit does). The ionizer is nice, otherwise I would have given it 1 star.