Austin Air Replacement FiltersAustin Air Replacement Filters All our filters are designed to last up to 5 years under normal residential use. Replacement filters for all standard size models are available below. You can check the size of your existing filter by looking for a label on the bottom of the unit. Model HM400 indicates standard size filter. Still not sure which filter you need? Filter and Pre filter included. Our Standard size filters measure 14. 5 high. Feel like an