How often do I need to replace my filter?

Since this is showing a picture of our SUN AIRE purifiers we build here in AMERICA, it is important for all to know our pre-filter are LIFETIME/WASHABLE 0.5 micron 2-stage electrostatic and NEVER need to be replaced. Our pre-filter serves two purposes; to filter your air down to 0.5 microns and also to keep the inside of your SUN AIRE purifier unit CLEAN and MAINTENANCE-FREE! Simply take the filter to your sink; spray it with your sprayer pushing the particulates out; let the water drain out the two drain holes on the end of the aluminum frame; wipe it with a towel and put it back on your unit. NEVER needs to be replaced and you save about $100-200 per year in expensive replacement filters with SUN AIRE purifiers!