Sorry about the slow reply. It depends on how much dust is in the air. I live in an older home on a gravel road surrounded by forest so there's a lot of dust an

Sorry about the slow reply. It depends on how much dust is in the air. I live in an older home on a gravel road surrounded by forest so there's a lot of dust and pollen. It only takes about a week to start seeing some color in the filters. I use the paper disposable filters so washing them isn't an option.