Understanding the Right Size and Type of Media for MERV Rating

The MERV rating scale is a standard measure of a filter's ability to remove particulate matter from your home air. It ranges from 1 to 20, with lower ratings indicating a lower quality filter. If chemical disinfectants are used, they should only be applied with the air conditioning system turned off and not to ventilation filters. The effects of disinfectants on filter performance are unknown, so they should only be treated with disinfectants if they are going to be removed from service and discarded.

Ultraviolet (UV) systems are quite effective at maintaining the cleanliness of HVAC coils, drain trays, and other damp surfaces. Properly designed systems can be very effective at inactivating microorganisms in moving air currents on the fly. These systems generally require more lamps so that they can provide significant doses of UV in a short period of time. A typical single-pass inactivation efficiency is 85%, much like that of a good particulate filter, but systems can also be designed for inactivation greater than 99.9%.Another way to install UV is in an “aerial” configuration.

Specially designed wall-mounted accessories create an irradiated area above the occupant and disinfect the air in the space as the air circulates naturally, mechanically or through the HVAC system. The CDC has approved this type of system for use in TB control for nearly 20 years, and there is guidance from the NIOSH on how to design them. Mobile UV systems are also frequently used for cleaning terminals and disinfecting surfaces in health centers and other spaces. Designing and sizing effective ultraviolet disinfection systems can be a complex process due to the need to determine the dose administered to a moving air stream or to an irradiated region of a room. Inlet systems are further complicated by the configuration of the air handling unit and ducts and reflections from surfaces, which can help achieve higher irradiance levels.

Superior air systems require an adequate air mix to function properly, while paying close attention to reflective surfaces that could cause room occupants to be overexposed to UV energy. Accredited manufacturers and system designers can help by making the necessary calculations and designing specific systems for individual spaces. Regular air filter changes are essential to keep your system clean and running efficiently, as well as to keep your energy bills under control if you have an oven, air conditioner, or heat pump at your home. However, a filter that is too dense for your setup can make it difficult to effectively and efficiently heat and cool your home. If the existing filters fit perfectly, note (or take a picture) of the size printed on the filter frame. There's nothing unique about these filters that are anti-allergic, and other filters with the same MERV rating should capture allergens just as well.

The following table provides the approximate relationships between the classifications according to ASHRAE's MERV and ISO 16890 test methods. Be sure to install the new filter facing the right direction, look for arrows on the filter frame that indicate the direction of air flow. You can help minimize the risk of HVAC equipment problems or damage from a pressure drop by changing your air filter regularly. The air filter is normally located in the fan compartment, between the air return and the furnace or air controller itself. There are no published laboratory studies showing whether the SARS-CoV-2 virus can be re-aerosolized from ventilation air filters or other HVAC surfaces. The initial filter pressure drop (initial resistance) will vary depending on filter type, MERV rating, and size.

As the rating increases, filters can progressively capture smaller particles and tend to cost more. Understanding MERV ratings is essential for ensuring that your home has clean air circulating through it at all times. It is important to know what type of media is best suited for your particular MERV rating needs as well as what size media you should use for optimal performance. Additionally, it is important to understand how often you should change your air filters in order to keep your HVAC system running efficiently while minimizing any potential damage caused by pressure drops.

Finally, it is important to understand how UV systems work in order to ensure that your home is properly disinfected from airborne pathogens such as SARS-CoV-2.