The right time to change the furnace filters depends on several factors, such as the thickness of the filter, the quality of air, your house's size, and whether you have any pets.
As per the expert's recommendation, if the thickness of your filter is less than 2 inches, it needs to be replaced every three months. However, if the thickness is 3 to 4 inches, it can be replaced after 6 to 9 months. And, if it is 6 inches thick, it can go for even a year.