I recently had the air ducts cleaned (whew!, no wonder I've had the sense of breathing dust) that are associated with an 11 year old Payne gas heater. The inbuilt filter (?) is a coarse mesh rectangular piece held down by flimsy wire spring and that would hold back something a little smaller than a marble [the filter is also held in place by sheet metal protrusions in the back of the floor of the heater that require the back of the filter to have two rectangular cutouts that create a poor fit in an already poor filter]. So it's clear I need a real filter. BUT the place in the Payne for a filter doesn't allow for sliding a real filter in to be flush with the floor of the heater (didn't Payne really think of filtering all that dusty air they're pumping through the house?) and a sheet metal edge on the botton rolls up at the edge of the opening making if difficult to install, seal and hold down a real air filter down. On the other hand, the 6 1/2 x 27 air register in a tract home was simply cut into drywall and has no frame to hold a filter. Not only that but the bottom of the hole in the wall has no stud and one side has a foundation bolt making fabricating and attaching a frame inside the wall kinda tricky)... I've thought of all kinds of fabrications to allow installation of a good filter, none of the ideas so far being very elegant and satisfactory. It's hard to imagine that someone hasn't noticed and dealt with this issue and come up with a better idea than I've had so far. Would be grateful for your ideas, experience that would help get a good filter in my heating system. Thanks.