HEPA Filters and Home HVAC: What They Are and Whether Your System Can Use One

What a HEPA filter is

EPA says HEPA is a type of pleated mechanical air filter that is common in portable air cleaners, also known as air purifiers. EPA says the name is an acronym for high efficiency particulate air filter, as officially defined by the U.S. Department of Energy.

EPA says the 0.3-micron particle size in the HEPA specification is the worst case, the most penetrating particle size. It says particles that are larger or smaller are trapped even more efficiently.

EPA's technical summary on home air cleaners describes how the filter is built. It says HEPA filters have very deep pleats with a much larger surface area than conventional pleated filters.

HEPA versus a MERV-rated furnace filter

MERV stands for Minimum Efficiency Reporting Value. EPA says it reports a filter's ability to capture particles between 0.3 and 10 microns. The test comes from ASHRAE, the American Society of Heating, Refrigerating and Air Conditioning Engineers. The full MERV scale is explained in HVAC air filters.

The two labels are separate systems. EPA's MERV page says its HEPA figures are not based on the MERV rating system. EPA's technical summary adds that filters described as HEPA in home air cleaners are generally equivalent to MERV 16.

The same summary says there is no widely accepted definition of HEPA performance in consumer products. It says home HEPA filters are unlikely to match the HEPA systems used in health care buildings and industry, though it says they still have very high removal efficiency for the particle sizes tested. CARB also warns that high-efficiency filters are sometimes mistakenly called HEPA or True HEPA.

Can a home HVAC system use a HEPA filter?

Sometimes, but it may take changes to the system. CARB says HEPA filters require correctly sized fans and central duct work. It adds that they are becoming more readily available for home central forced air systems.

The problem is resistance. A high-efficiency filter adds resistance to the airflow. EPA's technical summary describes these as higher pressure drop filters. EPA's technical summary says that, for existing systems, a HEPA filter may require changes to the ductwork to fit the thicker filter. It says a more powerful fan may also be needed to overcome the higher pressure drop.

EPA says existing home systems may lack the fan capacity for these filters without cutting airflow. It says that can mean lost cooling or heating capacity. It also names an increased risk of component failure and comfort problems.

For new installations EPA says to check the HVAC maker's information. In existing homes, it says airflow can be measured against the equipment's airflow and pressure capabilities, and that this should be done by a professional. It adds that simply installing a high-efficiency filter does not mean it will work as intended.

EPA says high-efficiency filters require well-sealed frames to prevent leaks. EPA says incorrectly designed or installed frames can cause bypass airflow, which significantly decreases filter effectiveness.

Why a MERV 13 filter is usually the practical choice

A filter in your system only works while the fan runs. EPA says furnace and HVAC filters filter the air only when the system is operating. Its technical summary says they will not filter the air when the fan is off.

EPA's technical summary says that, because of this, most MERV 13 filters are likely to be almost as effective as HEPA filters for most indoor particle sizes. It also says field studies have not yet confirmed that home system fans run long enough to demonstrably improve health outcomes.

EPA's consumer guide says most systems can take a MERV 13 filter without equipment problems, provided it is replaced frequently. It says systems are not commonly labeled with filter recommendations, so a technician can confirm the limit.

Running the fan longer is not free either. EPA says longer run times increase electricity use. It also says they may give less reliable humidity control during the cooling season. See why a house feels humid with the AC running.

Portable HEPA air cleaners for one room

EPA says portable air cleaners are designed to filter the air in a single room or area. It says they often reach a high CADR by using a HEPA filter. CADR stands for clean air delivery rate. EPA says most portable air cleaners are rated by it.

EPA says to choose a unit with a CADR large enough for the room. EPA says to put it in the room where people spend most of their time, such as a living room or bedroom. CARB adds that portable units are usually best for single rooms, not the whole house.

EPA says several studies of portable HEPA air cleaners found small improvements in heart and breathing health, and that the improvements are typically small and not always noticeable to the individual. Studies also found improvements in one or more allergy or asthma symptoms. The studies do not always show major improvements, and they do not show improvements in all symptoms.

EPA says to avoid air cleaners and filters that intentionally produce ozone, which it calls a lung irritant. EPA does not certify or recommend specific brands, and neither does this page.

Questions to ask before a whole-house HEPA upgrade

CARB says to contact a contractor experienced in designing and installing central filtration systems. It says to request a system that is low-leakage, easy to maintain, energy efficient and ozone free. These questions follow from the sources above.

1. Does the equipment maker's documentation allow a HEPA or MERV 16 filter on this system?
2. Will you measure airflow against what the equipment can handle, as EPA describes?
3. Does the plan need duct changes or a stronger fan?
4. Is there a pre-filter? CARB says a low-efficiency pre-filter upstream can prolong a HEPA filter's life by preventing rapid overloading.
5. Is the filter frame sealed so air cannot bypass it?
6. Can the fan run at a lower speed for filtering? CARB says some systems have a two-speed or variable speed fan for that purpose. See variable speed air handlers.
7. Would a MERV 13 filter or a portable HEPA unit meet my goal instead?