Air conditioners can shut down if fine filters restrict air flow. The air conditioner is also stressed by a dirty filter that slows down air flow, making the system work harder. Also, your system may not be able to deliver enough heating or cooling to the house. Or just the far one or two rooms get uncomfortable.
MERV is a rating of a/c and furnace filters and that standard compares filters. Different material have pores much smaller, to allow the filter to remove pollutants, creating more resistance that wears the equipment. The deeper pleated filters allow the dirt to be spread over a larger surface area, reducing pressure drop and making it possible to change the filter less often without significantly affecting system performance.
Blocked filters make it harder to keep you warm or cool—wasting energy. A clean filter will also prevent dust and dirt from building up in the system.
Some air conditioner filters with a high MERV rating can drop air pressure in your duct system, which can increase energy bills and damage your HVAC system.
For example, a 13 MERV filter is 1 inch thick. Because the filter is thin and the MERV is high, it reduces airflow into the duct system, and will quickly fill up with particles and block airflow. But if the filter was thicker 2 inches, it would have more surface area to allow more room for air to pass through and not restrict air flow.
MERV, minimum efficiency reporting value, is the standard that measures the effectiveness of air conditioner filters. Fine filters mean smaller pores to remove pollutants, creating resistance stress that wears out the equipment. Then the filter starts to get dirty creating more resistance. Many air conditioner manufacturers recommend using an air filter with an 8-9 MERV rating to balance the filtering air allergens with the cost and stress on the HVAC system.
The MERV rating scale range is 1-16.
Low quality fiberglass filters are 1-4 MERV.
Residential systems will use air filters with MERV ratings from 7-12.
Commercial buildings are higher at MERV range of 5-16.
High-Efficiency Particulate Air (HEPA) filters in hospitals and research labs are at 13 -16.
Higher MERV rated filters have finer holes to stop allergens. But, the smaller the hole lets less clean air can pass through the HVAC system. Even less clean air passes through as it gets dirty. Restricted air flow puts stress on the fan and compressor, is less cool, and costs more to operate longer. Low range filters, 5-8 MERV, screens common household allergens like dust, pollen, mold, and pet dander.
Mid range filters, 9-12 MERV, screens cigarette smoke.
Many manufacturers recommend using at 8-9 MERV rating, you maximize filtration of the environment and expense of operational costs and equipment stress.