The Austin Air PERMAFILT Pre-Filter is designed to last for years. Once installed, the Pre-Filter can be easily maintained by occasional vacuuming from outside the perforated steel housing of the Austin Air unit. This procedure keeps the Permafilt Pre-Filter clean. It also increases the life expectancy up to 2 or 3 years, eliminating costly quarterly filter changes. Periodically vacuuming the outside of the machine clears away the larger and most visible dust which properly maintains the effectiveness of the filter.