A:Answer The HEPA-Type filter of this unit will need to be replaced every 6 to 8 months. However, if you upgrade to a True-HEPA filter, you will only need to change it every 12 to 18 months. The Holmes AER1 replacement filters, that are compatible with your unit, typically range in price from $17.99 to $19.99 each. Thank you for your inquiry.