Changing out 14x20 return duct to 20x20" and would like to use the 4"+ media filters instead of 1". Haven't found a source for 4"+ media filter grill box. Manufacturers of filter boxes don't seem to offer this option that I found. Honeywell makes 4"+ filter which is tapered in so you can be used in standard grill box but this presents sole source option for filter media which could be problem.
Anyone know who is making 20x20 grill boxes that can accept upto 5" filter media?