you don't have to change the EAC filter unless thess strings are broken, but you do have to clean the EAC filter every three month.
Cleaning procedure:
Procedure: 1. Turn off the power for the Furnance; 2. Swich off the power for the EAC; 3. Carefully remove the TWO filters and screen; 4. Rinse the Screen with water ; 5. Rinse the filters with water; 6. Spry the filters with the FANTASTIC 9cleaning agent); 6. Carefully brush the filters (The ss-strings are easily to be damaged); 7. Air dry the cleaned parts; Put them back to the EAC as the AIR FLOW DIRECTION: 
Cleaning procedure:
Procedure: 1. Turn off the power for the Furnance; 2. Swich off the power for the EAC; 3. Carefully remove the TWO filters and screen; 4. Rinse the Screen with water ; 5. Rinse the filters with water; 6. Spry the filters with the FANTASTIC 9cleaning agent); 6. Carefully brush the filters (The ss-strings are easily to be damaged); 7. Air dry the cleaned parts; Put them back to the EAC as the AIR FLOW DIRECTION: 