How long is "average use?"

[ihaveanosebleed]

Also, about PS1's ....

They don't have any fan sucking in the dust!

Well just make sure your fan is going the right way before placing a filter. It shouldn't be hard to tell, You want the filter over the air INTAKE. It might be easier, actually to have the fan reversed and pull air in from the back, and have a nice square filter in the back. If you use foam try to find something very light and breathy but I’d go with a fiber filter for a furnace or something.