I have a 1940 home with a basement and a forced air heat pump system that was added some time in the past decade by the previous owner. The ceiling in the basement is open, and the ducts were installed inside the joists in the basement. There are two large grills, one on the main level, and one in the basement that connect to the return air duct. The return air duct, appx. 16" in diameter, appears to be expoxied to a square 20x10" vent that's connected to the air handler.
Unfortunately, there's no proper filter bracket or rail. It appears the previous owner simply cut a hole in the square vent and set a 20x20 filter into the hole without any sort of sealing or cover.
I bought a new 20x10 filter and set it in this hole, but there's nothing on the top or sides in the vent to support it, and no cover to seal the hole.
Is there a feasible way for me to install the appropriate filter bracket to this system?