Pretty simple, the main air intake is under the rear square stand-off panel. Very restrictive for some reason, maybe to keep birds out!. I am going to play with several solutions, but the simplest will be a box filter larger than that rear panel that simple mounts over it. I happen to have a 10x20" house furnace filter right here. It's almost the exact size of the rear cabinet, but is too big. I will cut it down into 2 or 3 filters and loosely mount them. Suction should seal them off using the giant squirrel cage fans I got with this. Maybe drill some holes in the panel. I could calculate all this, but intake area is way smaller than the top hose connection, which is also way smaller than the fan intake. A lot of velocity at the filter and inside the lamp chamber. Maybe I will stick a T-couple in there to see what actual temps are.