When it comes to air conditioning systems, it is difficult to give exact recommendations without consulting the owner's manual. Most homes should work well with a MERV 8 to 13 filter, which can remove most unwanted particles without placing a burden on the system. For households with few occupants and no pets, a MERV 8 filter should be sufficient. However, if there are more people and some pets in the home, a MERV 11 filter is recommended.
If someone in the household has a weak immune system, it may be necessary to use a MERV 13 filter for their health and well-being. The MERV standard is mainly used to measure the performance of filters designed for forced air conditioning systems. HEPA (High Efficiency Particulate Air) is a much stricter standard than MERV. HEPA filters have such tight filtration that they tend to restrict airflow too much for most residential forced air systems.
They are often used in air purifiers and vacuums instead. A Merv 13 filter has even smaller pores than a Merv 11 filter, so it can remove all the larger particles that a Merv 8 filter removes, as well as the even smaller particles that only a Merv 13 filter can remove. For example, mold spores range from 2 to 10 microns and MERV 8 will remove some of this contaminant while MERV 11 will eliminate all mold spores. The secret is that they can capture tons of waste while using a relatively porous filter material due to the enormous surface area where dirty air has to pass approximately four times as much filter material as a 1-inch filter.
Most home improvement stores sell air conditioning filters ranging from MERV 1 to MERV 13, although CR has tested models as tall as the MERV 16. With the MERV 13, the highest rating you'll find for most popular residential HVAC filter sizes, you can count on the filter to stop bacteria, smoke, and other microscopic particles. According to the Environmental Protection Agency, filters with a MERV of 7 to 12 are as effective as true HEPA filters at removing most airborne particulates. This is why it is not recommended to use a MERV 20 air filter in homes that are not built to withstand this level of filtration. However, some filters with medium and high MERV ratings can cause problems in residential air conditioning systems.
We believe that the concerns of manufacturers are a bit exaggerated, in part because a recent innovation in air filters allows for high MERV ratings (11 to 1) with a low pressure drop. In a conversation about the most common filter levels sold in retail stores, MERVs from 1 to 16, Owen said that this range “ranges from filters that can catch a golf ball (I'm exaggerating a little) to filters that catch just about anything.
