Yes, HEPA filters can remove viruses from the air. A true HEPA filter captures at least 99.97% of particles at 0.3 microns, and counterintuitively, it catches even smaller particles (including most viruses) with greater efficiency. The real-world effectiveness depends on how much air the filter actually processes in your space and how quickly it does so.
Why 99.97% Is the Worst Case, Not the Best
The most common misunderstanding about HEPA filters is that they work like a net with holes of a fixed size, letting anything smaller slip through. That’s not how they function. HEPA filters are tested at 0.3 microns because that’s the hardest particle size to catch, known as the most penetrating particle size (MPPS). Particles larger than 0.3 microns slam into the filter fibers or get snagged as airflow bends around them. Particles smaller than 0.3 microns, including most viruses, are so lightweight that they zigzag randomly through the air in a phenomenon called Brownian motion. That erratic movement makes them more likely to collide with and stick to filter fibers, not less.
Most viruses range from 25 to 400 nanometers in diameter (0.025 to 0.4 microns). SARS-CoV-2, for example, is roughly 100 nanometers. That puts it well below the 0.3-micron threshold, in the size range where HEPA filters actually perform better than their rated 99.97%. The U.S. EPA confirms this directly: particles larger or smaller than 0.3 microns are trapped with even higher efficiency.
Lab Results With Live SARS-CoV-2
Researchers at the National Center for Global Health and Medicine in Tokyo tested a HEPA air cleaner against live, infectious SARS-CoV-2 aerosols inside a biosafety level 3 chamber. The filter removed 85% of the airborne virus after 5 minutes, 96% after 10 minutes, and over 99.97% after about 35 minutes. The longer the filter ran, the more completely it scrubbed the air, because each pass through the filter caught additional particles that had escaped earlier cycles.
These numbers reflect a real room scenario, not just a single pass through the filter media. They show that HEPA filtration works against actual respiratory viruses, not just inert test particles. The study also tested a copper-coated HEPA filter designed to inactivate viruses on contact, and it performed comparably, reaching over 99.99% removal in the same timeframe.
HEPA Filters vs. HVAC Filters
Standard home HVAC systems use filters rated on the MERV scale, typically MERV-8 in residential settings. Upgrading to MERV-13, which is the highest rating most home systems can handle without airflow problems, makes a meaningful difference. In a controlled study of enclosed spaces, MERV-13 filters reduced the estimated probability of COVID-19 infection by about 42% compared to MERV-8 filters. Adding a portable HEPA air purifier on top of the MERV-13 filter pushed that reduction to 50%.
Interestingly, the same study found that using a portable HEPA purifier alongside a basic MERV-8 filter had little measurable impact on infection risk. The purifier alone couldn’t compensate for the poor baseline filtration. This suggests that for virus reduction, upgrading your HVAC filter to MERV-13 is the higher-priority step, with a portable HEPA unit serving as a useful supplement rather than a standalone solution in spaces with central air systems.
What “Removes Viruses” Actually Means in Practice
A HEPA filter captures virus-laden particles that pass through it with extremely high efficiency. But it can only filter air that actually reaches it. In a room, air doesn’t move through a purifier all at once. Virus-containing aerosols from a cough or exhale may linger near a person for seconds to minutes before drifting toward the purifier’s intake. This is why placement and airflow rate matter as much as filter quality.
The EPA recommends choosing a portable HEPA air cleaner sized for the room where you’ll use it. Look for one of three things on the label: a HEPA designation, a Clean Air Delivery Rate (CADR) rated for smoke (the smallest particle category), or a manufacturer statement that the device removes most particles below 1 micron. A unit that’s too small for the space will cycle air too slowly to meaningfully reduce your exposure before you breathe it in.
Viruses also don’t travel alone. Respiratory viruses ride on droplets and aerosol particles that are often larger than the virus itself, sometimes 0.5 to 5 microns or more. These are well within the size range where HEPA filters are most efficient, which means real-world virus capture may be even easier than the bare viral diameter would suggest.
Limitations Worth Knowing
HEPA filters remove virus particles from the air, but they don’t eliminate every route of transmission. They won’t help with viruses picked up from contaminated surfaces, and they can’t protect you from a nearby person’s direct cough or sneeze before those droplets disperse into the room’s airflow. Filtration works best for reducing the background concentration of virus in a shared indoor space over time.
The filter also needs to be in good condition. A clogged or long-overdue HEPA filter restricts airflow, which means less air passes through per minute and more virus stays suspended in the room. Most manufacturers recommend replacing the filter every 6 to 12 months depending on use, and following the instructions in the manual is the simplest way to keep performance consistent. When you do swap the filter, handling it gently and placing it directly in a bag minimizes any chance of disturbing trapped particles.
Finally, watch for products labeled “HEPA-type” or “HEPA-like.” These are not held to the 99.97% standard and may have significantly lower capture rates. Only filters meeting the true HEPA specification (99.97% at 0.3 microns in the U.S., or 99.995% under European EN 1822 standards) deliver the performance described here.