The Air Inlet filter is a replaceable filter for use with the Respironics EverFlo Oxygen Concentrator. Air Inlet Filter is to be changed every 24 months. The Filter Door should be cleaned MONTHLY or as environmental conditions warrant. Whats Included: 1x Original EverFlo Air Inlet Filter * NO RETURN & NO REFUND POLICY Please check if you have ordered the right size/type of product as we practice NO RETURN & NO REFUND POLICY due to health and hygiene concern, to give our customers peace of mind.  Thanks for your understanding. Feel free to contact us if you have any enquiries before placing your order. 😊 Like us on https://www.facebook.com/yikenmedical #yiken #yikenmedical #philipsrespironics #everflo #oxygen