Most residential and commercial applications use a 1” filter in their HVAC systems. This is what we would consider to be “bare minimum”. Filters are sold by size and with a MERV rating - “Minimum Efficiency Reporting Value”. This rating equates to the effectiveness of the filter. The higher the MERV, the finer the filtration; but also, as the MERV increases, so does the restriction to air flow. The operation of the HVAC system relies on clean, filtered air, and a specific amount, to flow through the system. The better the filter - the cleaner the air. The cleaner the air - the less demand for cleaning the heat exchanger. This saves the customer in maintenance costs and prevents the losses in efficiency from inadequate air flow and system operation. It is important that filtration is sized and installed properly for the specific amount of air flow demands for each system. Our BETTER media filters that we sell are MERV 8-13.