HEPA high-efficiency particulate filters are renowned for their ability to remove up to 99% of the smallest air particles. However, due to their dense filtration material, they can be too restrictive for furnaces. Installing a HEPA filter in your furnace is not recommended, as it would significantly reduce airflow. High-quality air filters with the right MERV or MPR rating can prevent outdoor air pollutants from entering your home, while also filtering the air that is recirculated inside the house.
This helps to keep indoor air clean by removing allergens, pathogens and even some viruses such as COVID-19. A dirty filter can restrict airflow, preventing the system from working properly and eventually leading to equipment failure. Air exchangers (and their filters) are important for removing airborne particles or aerosols (such as Covid droplets) to protect air quality for occupants, as well as removing moisture from the air. HEPA filters are highly effective at cleaning the air, but there are other types of filters available too. Electrostatic filters and electrostatic precipitators use a small charge to trap particles.
The Minimum Efficiency Report Value (MERV) is used to rate the efficiency of an air filter. For example, hospitals often use HEPA filtration to prevent viruses from circulating in the air. In most cases, MERV 11 provides the best balance between stopping fine air particles and avoiding damage to the furnace. Furnace filters do an essential job of keeping the furnace working properly and ensuring better indoor air quality.
Remember that the same air will pass through the filter several times a day, so it's important to choose a filter that won't impede airflow or cause damage to the furnace.