Our Air Doctor filter Genuine Ultra HEPA filter fits in both our AirDoctor AD3000 and AD35000 units. The airdoctor filters: Genuine AirDoctor 3000 filter and 3500 Replacement HEPA Filters, AIRDOCTOR AD3500 Universal Genuine Replacement Filters are the only filter third-party tested to provide stated results in our airdoctor air purifiers. Genuine air doctor ad3500 replacement filters and air doctor 3000 replacement filters are a must for keeping your unit running at tested levels. The AirDoctor filter captures 99.99% of airborne particles at 0.003 microns, 100x smaller than the HEPA standard. AirDoctor 3500 filters are made to be used with - and third-party tested with - the airdoctor filter, so always use the air doctor 3500 replacement filters to ensure your unit runs as expected. Bring hospital-grade ultraHEPA filtration to your indoor environments with the air doctor ad 3500 filter.