What is a MERV rating?
MERV stands for Minimum Efficiency Rating Value. This is an industry standard rating system that allows you to compare filters made by different manufacturers. A MERV rating is a numerical value ranging from 1 (lowest efficiency) to 20 (highest efficiency) and tells the consumer how well the filter captures and holds dirt and dust of a specified size range. The chart below shows the MERV ratings, corresponding particle size ranges, and efficiency level as measured by the percentage of particles captured.
How Should I Choose A MERV Rated Air Filter?
A lower MERV Rating, implies a lower filter efficiency, but also lower costs in running the unit. Conversely, a higher MERV Rating, implies a higher filter efficiency and usually means higher costs to run the unit. On moving from MERV 1 to MERV 20 you increase the filtration efficiency (ie. the amount of dust the air filter is able to capture) due to the media becoming less porous.Because of this decreasing permeability, your unit will be required to cycle on more often in order to maintain the same amount of airflow passing through the system. This causes more energy to be used, raising your operational costs.
Should I use the highest rated filter available?
No. You should use a filter rating that corresponds to the requirement of your HVAC system. If you are not sure contact your installer and HVAC maintenance company. Using a filter rating that is too high for your HVAC system may cause damage. Higher rated filters offer resistance to air flow that may place too much strain on the fan motor in your air handler, leading to HVAC system failure. Using a filter rating that is too low will prevent you from maximizing the level of clean air in your home.It is worth the effort to get this right. Call your HVAC system installer or maintenance company and ask them what air filter MERV rating they recommend for your system.
What is HEPA Filters?
HEPA Filters stands for "High Efficiency Particulate Air" filters. Basically HEPA is a type of filter that can trap the smallest particles (0.3 micrometers (µm) in diameter) that other air filtration systems would simply re-circulate back into the air of your home. HEPA filters remove 99.97% of all airborne particles that can cause problems for allergy and asthma sufferers, reducing or eliminating them to make the air cleaner for those residing in your home. In the 1950’s during WWII, HEPA filters were invented by the US Atomic Energy Commission (AEC), who needed something that would remove small radioactive dust particulates from the air. In the last decade HEPA-technology air purifiers have been used to clean indoor spaces from homes to beauty salons to hospitals and operating rooms across the country. The Environmental Protection Agency (EPA) as well as the Occupational Safety and Health Administration have endorsed the HEPA filter as being the absolute best filter in cleansing the air.
How is HEPA made and how does it clean air?
The difference between a HEPA filter and other filters is that HEPA filters are made of thin fibers of glass, and contain some level of activated carbon-based material. The fibers of the filters are formed into a thick paper-like material that is pleated, with some HEPA air filtration systems having as much as 40 square feet of the folded filter material in the HEPA system. As particulates in pretreated air attempt to pass through the filter’s thick, folded surface they cannot; instead, they adhere to it.
Will I save money using a more efficient filter?
Very likely. Experts have estimated that the average cost savings derived from using a high efficiency filter is approximately 10%. This cost savings includes the reduction in fuel consumed by your HVAC system, and reduced repair and maintenance costs. This does not include the cost of system replacement resulting from failure to replace your filter.
How long will a HEPA Filter last?
Filter life depends upon the operating conditions. A general recommendation is that, at minimum, the filter be replaced when the pressure drop reaches two times the initial pressure drop (assuming ‘normal’ design airflows). HEPA filters that are not subject to high contaminant concentrations may have an indefinite life, depending on the operating conditions. HEPA filter life due to prefilter drop in efficiency over time due to inherent charge dissipation of the media. Wet filters should be replaced as soon as possible and the conditions that caused the filter to become wet should be corrected. Filters that are allowed to remain wet for 48-hours or more could be subject to mold growth within the media. The construction components of the filter are inert to contaminant amplification. Filters that are allowed to dry after being wet may have a higher pressure drop when compared to their pressure drop before they were wet.