Have HVAC Questions? Ask an HVAC Expert for Answers
Your filter part number is XXXXX 18-32.....it is a 15x21.
This is one of the things that irk me. Filter sizes made by mfg that are not standard. You cna find them in stock at Goodman dealers or have the hardware or heating contractor order them. Usually folks will get a case of them. In areas with a lot of modular home communities they are more prevalent.
You can lso order online by google terms 15x21 filter. Some are also washable/reuseable. I wishthe mfg just used basic sizes available at the home improvement stores...