When it comes to air conditioning systems, the Minimum Efficiency Reporting Value (MERV) rating is a measure of how well a filter can prevent dust and other contaminants from entering the air stream. A residential system typically won't accept filters with a MERV rating higher than 12, unless it has been upgraded for a higher-efficiency filter. Low-efficiency filters usually have a MERV rating between 1-4, while high-efficiency filters are rated at MERV 13 and above. Using an air filter with a MERV rating higher than what is recommended by the manufacturer of your boiler or air conditioner can actually reduce its performance.
An air filter with a higher MERV rating can block microscopic particles, such as smoke molecules, due to its tighter mesh structure. Filters with a MERV rating greater than 13 can filter particles that are closer to 0.3 microns in size. Another undesired effect of this decrease in air flow occurs on the cooling side. The air conditioner has a hot coil on the outside, the condenser and a cold coil inside the air controller.
This cold coil has an optimal operating temperature that is based on a certain amount of hot air flowing through that coil and on the coolant that runs through the copper tubes of that coil. With a higher MERV filter that reduces air flow through this crucial part of the air conditioning system, the cold coil can freeze and form an ice ball, completely restricting air flow. Without giving more details, this causes more expensive problems in the outer condenser coil. MERV 13 or higher air filters are recommended for those who prioritize air quality and may need to treat cases of asthma, serious allergies, and other similar circumstances. Any air filter rated higher than 13 will restrict air flow to the point of causing damage to the air conditioning system, which would entail an additional expense to repair it.
Keep in mind that as the MERV rating increases, the filter becomes more restrictive and more pressure and energy will be needed to expel air. Although ratings do not exceed those of the MERV 16, high-efficiency particulate air (HEPA) filters trap even smaller particles at a speed even higher than that of the MERV 16 and are generally used in surgical operating rooms, clean rooms, and other contexts that require absolute cleaning. Some technicians anticipate that people will forget to change filters, and regular use of low-efficiency filters could help minimize damage to neglected air conditioning. A more efficient filter will be more effective at removing particulates from the air as they enter the air conditioning system. Different sized air filters will have different prices, as will those with different MERV ratings. In general, filters with a MERV 16 rating or lower are considered suitable for residential, commercial, and general hospital use.
