Good to know. I have the kind that only needs to be changed twice a year but I might pick up one to have for spring.I went to the hardware store today for a furnace filter and they were completely out of the size I needed. The employee told me the warehouse is empty and they don't know when or if they'll be getting them in. So I went to a larger chain store with a wider selection. I not only found one but they were on sale for a great price so I bought two. I found out the reason they're in short supply is due to a fiberglass shortage. Glad I bought two because I wouldn't want to get stuck in winter without a filter for the furnace.