I've been noticing a lot of dust in the air at my apartment (even after vacuuming regularly) and generally not feeling so well so decided to inspect the air conditioning system;

The air conditioning unit is situated in the roof cavity by our door and sucks up a lot of dusty air through the doorway from the apartment hallway;


Filter removed:


The unit has a 4-layer metal mesh filter with aluminium frame which only catches very large particles and lets most of the dust through into the system:


The air exits two ceiling air diffusers;




I've just finished cleaning the air conditioning fan, filter, air diffusers and toxic-looking mould from the shafts above the diffusers.

I want to install some filters (like a washable HEPA filter) that will actually catch all the dust and cr@p and remove it from the air instead of just blowing it around the place.

What do you think is the best way to go about this?

 

1. The metal filter has a bit of room in the frame where I could stuff some filter fabric in to act as another filtering layer however I'm not sure where to get this from.
2. Unless I can just get a better filter to replace it (measures 225x840x12mm) however also not sure where to get this from.
3. I also have the option of adding some filters or some sort of filtering fabric to the air diffusers however I'm not sure how any of these option will affect the performance of the air conditioning unit.