When it comes to air filtration, the general best practice is to use the thickest possible filter for maximum efficiency. But, never try to force an air filter to fit in a space it's not designed for. 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 be worse. To better understand this concept, let's compare 4-inch vs 1-inch oven filters.
In a broad sense, this is a comparison of “thin filter versus coarse-grained filter”. Media filters work better because they have more surface area. These 4-inch media filters can have 20-30 feet of surface area with their pleated (accordion) filter material. This means they can trap more debris without clogging up as quickly.
A MERV 13 filter traps lint, dust, pollen, dust mites and their “debris,” mold spores, pet dander, smoke particles, and even droplets of moisture from sneezing. With most HVAC systems, you should be able to adapt a media filter cabinet, either under the oven or on the side. A 1-inch oven filter with a MERV rating of 6 to 8 will last up to 3 months even with fairly heavy oven use. If you choose a 1-inch tall MERV air filter, check it every month during the heating or air conditioning months, and change it when it's too dirty to see the light, or sooner.
When you want to improve air quality through better air filtration, but don't want the expense of modifying your equipment, a 1-inch MERV 13 filter does the job. Thicker oven filters, known as media filters, almost always perform better than cheaper one-inch filters. Poorly fitted one-inch filters where air passes around the frame (even causing the frame to bend and deform) are very common. First, 4-inch filters cover a higher range of MERV ratings, with a slight overlap with 1-inch filters.
For comparison, a 4-inch thick filter will have approximately twice as many surface areas as a 2-inch thick filter. Virtually any HVAC professional will tell you that thicker filters perform better than common 1-inch oven filters. Your HVAC technician can provide you with a new filter compartment or modify the existing one to accommodate the thicker filter. Therefore, if you have to install these thicker filters on a return grid, I would recommend having the return duct completely sealed and airtight. The more and smaller particles a filter traps, the faster it will fill with dust, pollen, pet hair, and dander, etc.
This upgrade is money well spent which will improve indoor air quality and ease the burden that air filters clog HVAC systems.
