Something else to do before the furnace comes on

[Ozz]

Greg, sometimes we have to balance the practical aspects of something like this, In my 3400RL, most of the dust, cat hair, airborne junk comes from our living area, so filtering the air from there is 90% of it.
My return is right under the stairs, not sure where yours is on your unit. Take a cigarette, or a smouldering...something, and hold it where you think the air might be going back to the furnace, the smoke being sucked away will show you.