I have two HP electrostatic air filters that fit into a designated air duct box. Older but working well. If you happen to have this system these filters are expensive and getting hard to find. Each is about 16"x12 1/4"x4 3/8"
got it from another Freecycler but couldn't use them
Pickup near 63rd and Fairview
Cross posted
HP air filters (Westmont)
This offer has been gifted to someone and is no longer available.