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HEPA Filter Testing: How and When to Test and Replace Your HEPA Filter


HEPA filters don’t last forever. Even ones that are supposedly “permanent” will still need cleaning to remain effective, and it’s possible to damage them during the cleaning process. To keep the air clean, HEPA filters need to be replaced from time to time. How do you know how much time each filter has? Well, there’s no specific time limit for HEPA filter life. They could last months or years. It’s all about the environment they are in and how much cleaning they do. 

Since lifespan isn’t based on time, to know when to replace your filter you’ll have to have some HEPA filter testing done. First, let’s discuss some basic signs you need new HEPA filters, then we’ll analyze how the pros do the testing.Download Complete Infection Control Guide

Signs Your HEPA Filter Needs Replacing

Some simple inspection is a great start and may save you a service call, especially if your filtration unit is easily serviceable.

Icon_HEPAFilters1. The Filter is Damaged

This seems fairly obvious, but it’s not something you’d see unless you were looking for it. You might have noticed strange sounds coming from the area around the filter, such as a high-pitched whistle. If your HEPA filters are remotely located, you might not ever notice the sound. A quick visual inspection can reveal whether your filters still have their structural integrity, so it would be a good idea to set up a routine schedule to check them out.

Icon_AIR2100_Airflow2. Power Consumption Rises

The motors in your filtration unit or HVAC system will have to work much harder to pump air through the filter when it gets clogged. You’ll notice the effects of this when you check your energy bills. The other issue is that this will cause more wear and tear on your system, so you can look forward to a repair bill sooner than you expected, too.

Icon_Bacteria3. Allergens are High

The job of a HEPA filter is to filter. When it’s clogged, torn, or otherwise on its last legs, it’s not doing the one job it has anymore. Microbes and allergens will not be filtered out anymore and building occupants will feel experience increased allergic reactions or worse.

Icon_DustAndDebris4. Dust and Dirt Build Up

This is probably the most obvious visual sign there is. The vents in your HVAC system or on your filtration unit will show a clear buildup of dust and dirt. So, not only will your HEPA filters need to be replaced, you’ll need to clean the vents, too.

HEPA Filter Testing

To truly ensure that your filters are doing their jobs, your facility should engage in regular maintenance and testing. Some processes can be performed by your staff, others will need to be handled by professionals. Proper long-term HEPA filter performance is dependent on accurate testing procedures, which is why it’s best to leave testing to the experts. When purchasing HEPA filtration units, it’s important to note that these tests are to verify not just that the unit was well built, but also properly installed. 

The Aerosol Test

The most common HEPA filter testing method is the “aerosol photometry test.” This test has existed since the 50s and is highly accurate. The way it works is a technician will spray a dispersed oil particulate (DOP) over the surface of the filter. The DOP must be sprayed in a perfectly uniform layer over the filter’s upstream side. 

Before the aerosol test can begin, however, the filter must have an established “flow rate.” That way, it’s possible to tell whether the airflow is too high or too low. Without that baseline rate, the test is no better than guesswork. Once the baseline is established and the test is complete, the tech can determine how large the leak is. The FDA says that penetration of just 0.01% is a significant leak.


What Aerosol is Used?

There are three aerosols generally used in HEPA filter testing, and they are:

  • Cold aerosols: These aerosols are largely a product of necessity, being made at the location of testing. The problem with cold aerosols is that it’s difficult to determine how many particulates reach the HEPA level of 0.3 microns. It’s still a useful test, especially for installations, but it’s not as accurate as a hot aerosol test. Because particles are of many different sizes, this process is called “polydisperse.”
  • Hot aerosols: Made from heated dioctyl phthalate oil. This process is excellent at creating a high number of 0.3-micron particles. Because the size distribution of the particles is so small, this process is called “monodisperse.”
  • Microspheres: Polystyrene latex spheres (PSLs) are increasingly popular for testing because they don’t have any carcinogenic effects, while oil-based aerosols do. They can be manufactured to have specific particle sizes for extremely accurate testing.

The ISO 14644-3 standard recommends 10µg/l and 100µg/l concentrations for aerosol photometry tests. Lower concentrations reduce sensitivity and while large concentrations increase the chance of fouling the filter. The testing techs need to get into the Goldilocks zone. 

Goldilocks Range Chart

How Are Leaks Found?

With a probe! There are two locations where the probe needs to be inserted to find where leaks may be happening. First is the gasket between the housing and the filter, and second is the filter face. The probe is looking for high concentrations of particles. If the concentrations are highest around the perimeter of the filter, there’s most likely an issue with the gasket. Solutions can vary, from simply re-seating the filter to replacing the gasket. If the filter face is the source of the leaks, it’s time for a new filter.

Again, this is a job for a trained professional. They’re going to take the proper steps to ensure that the test is performed properly and that none of the testing aerosol poses a risk to you, your staff, or any other building occupants. 

Get the HEPACART® Guide for Infection Control

To ensure you’re doing everything you can to prevent allergens and diseases from spreading, download HEPACART’s Infection Control for Facilities Managers: The Complete Guide. We know you take infection control seriously, and that’s we’re here as a trusted resource. HEPACART believes in clearing your air, so not only can you rely on us for knowledge and advice, you can rely on us to be hands-on. Give us a call and we’ll set up a schedule to re-certify your filtration units every year, test the filters, and give you tips on how you can maintain your filters for the best performance.

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