Furnace Filter Change Frequency Made Easy: Save Energy and Cut Down on Those Bills! How often to change the furnace filter? We hear this question all the time. The short answer is every 30 to 90 days for most pleated media. Sounds simple, but factors like wildfires, pets, and MERV... Furnace Filter Change Frequency Made Easy: Save Energy and Cut Down on Those Bills! How often to change the furnace filter? We hear this question all the time. The short answer is every 30 to 90 days for most pleated media. Sounds simple, but factors like wildfires, pets, and MERV...