What does the Merv rating on an air filter mean?
HOW AIR FILTERS CLEAN YOUR AIR
Filters are made up of filter media that contain layers of crisscrossed fibers. When air passes through the filter media particles are trapped onto the filter fibers. Depending on the size of these particles different filter mechanics are utilized to trap them.
Types of filtration mechanics:
Inertial impaction, Interception, Diffusion and Electrostatic attraction.
The two most important that pertain to everyday use are Inertial impaction and Interception. Larger particles impact the front face of the filter media. Smaller particles trap within the filter media through Impact and Interception.
How filters trap particles
MERV RATINGS
What is a MERV filter or MERV rating?
MERV "Minimum Efficiency Reporting Value".
MERV rating on an air filter describes its efficiency as a means of reducing particles of 0.3 to 10 microns. The higher the "MERV" rating means higher filtration efficiency or simply the better it is at trapping particles within that size range. MERV is a standard to allow an "apples to apples" comparison of various air filters.
Filters are rated on a scale of MERV 1 to 16,1 being the lowest and 16 the highest efficiency at removing particles in the range of 0.3 to 10 microns (inferring that filter has higher rating with particles larger than 10 microns)
WHAT FILTER SHOULD I USE?
Choosing the right filter generally is a balancing act between desired filtration and more importantly what your equipment is designed for. The higher the filtration (MERV rating) the more restrictive the filter is to airflow and this may impact the performance and life of your HVAC equipment. Without going to in depth on design of in suite fan coils and heat pumps, generally filters ranging from the non MERV rated Poly Wire (Most commonly used) to a pleated filter of a max rating of MERV 8 should be used. The use of higher rated filters (Merv11-13) put stress on the motors, reduces airflow which impacts performance and increases noise levels. The most important specification is size. Making sure the filter used regardless of type is sized specifically for your equipment. Using an improperly sized MERV13 filter will have less efficiency than using a properly sized Poly Wire.
Particles trapped by filter rating
Poly Wire -Typical supplied filter for in suite fan coils and heat pumps
Not Merv rated approx. equivalent to a Merv3.
Pleated filter - Upgrade filter not usually supplied for in suite fan coil and heat pump maintenance
General Merv ratings of 6-13