Ive ordered 13x21x1 filter but its larger than I do need and that is the size of my actual filter. Its very difficult to find that size. I be to cut it with a scissor but it works well so far
I've been using the cheap local big hardware store filters for years, but have been having congestion issues for the last couple years. I run a stand-alone air purifier, but thought (finally) to try a high quality furnace filter. It's only been a week, but I can tell a difference already.