The Minimum Efficiency Report Value, or MERV, is a standard rating of the overall effectiveness of an air filter. It measures how fine the filtration is, that is, how small are the particles that the filter can trap. A higher rating means that the filter can trap smaller air particles. Using an air filter with a MERV rating higher than recommended by the manufacturer of your oven or air conditioner may impair its performance.
The higher the MERV rating, the more efficient the filter will be at trapping these particles in the air. If you have one, make sure you get an oven filter with a MERV rating lower than your system's maximum. Filters with higher MERV ratings can remove more harmful contaminants from your home, but they can reduce the quality of the air you breathe if you select a filter with a MERV rating that is too efficient for your HVAC system. The worst percentage of the six tests is selected as the official measure used to determine the MERV rating of a filter.
When used in a multi-filter system, pre-filters trap dirt and large particles before air reaches the final filters downstream, removing the smallest particles. Most MERV 7 or higher air filters are effective at trapping dust, mold spores, tobacco smoke, pet dander and pollen. The air cleaner is literally a barrier between the HVAC system and the ventilation grilles, and that reduces the ability of air to pass through the vents into the actual system. Going above MERV 14 places the filter in the commercial category, and most residential HVAC systems can't handle them. Choosing an air filter with an appropriate MERV rating for your home is important for maintaining good indoor air quality. A filter with too low of a MERV rating won't be able to capture enough pollutants from your home's air, while one with too high of a rating can cause your HVAC system to work harder than necessary and reduce its efficiency.