Most air filters are 1 inch thick, but some systems can accommodate filters 2 to 5 inches thick. In our tests, we found that the thicker the filter, the better it performs and the longer the replacement intervals. This means it's better for you and your heating, ventilation and air conditioning (HVAC) system. Thicker air filters may automatically seem like the best choice, as more filtration is usually associated with greater thickness.
To put this into perspective, a 1-inch air filter may need to be changed every month, while a 4-inch air filter could last up to six months. The first important difference between 1-inch and 2-inch filters is their lifespan. Replacing the standard one-inch air filter with a 5-inch pleated filter can improve the air quality inside your home. This is because larger air filters have higher MERV ratings, leading to better filtration of contaminants and allergens.
The higher the MERV index, the smaller the contaminants a filter can trap, which also means it will clog up faster. Now, the more cubic feet per minute (CFM) of air that hits the furnace system, the more area it can cover with the heating or cooling action. Air filters with a thick media filter can trap small particles, such as pet dander and mold, without impeding air flow like a thin, pleated air filter would. If you try to use a 4-inch thick air filter for a system that is made for a 1-inch thick filter, the efficiency will actually be worse.
Opting for a 4-inch filter would mean that you would have a filter with at least a MERV 8 rating, which would remove contaminants down to 3 microns (a unit of measurement), including dust mites and some types of pollen. Pay attention to what matters most to you and you'll find out which filter is right for you. The second option is to double the filter area by inserting a second filter to power the fan from a second side of the unit or from below. Filter ratings range from 1 to 20 on the MERV scale (minimum efficiency report value), with a rating of 1 offering the lowest filtration.
