When it comes to our health and our environment, we all want the best.
Safe food and clean water still concern us, even though both are common in the modern world. Yet we only have a few meals and drinks over the course of a day. Breathing, on the other hand, is something we do a few times each minute.
Air surrounds us and affects not only our health, but also more sensitive equipment. In labs and hospitals, air quality is essential to getting work done right. We want clean air, but what kind of filter will get us the air we need?
Both HEPA and ULPA filters are very effective, removing particles smaller than we can see from our air. However, higher power doesn’t always mean higher efficiency, and ULPA filters’ higher ratings don’t always translate into cleaner air. With higher costs, sometimes ULPA isn’t the right choice.
What Are HEPA and ULPA Filters?
HEPA (High-Efficiency Particulate Air) and ULPA (Ultra Low Particulate Air) filters both clean the air by physically trapping contaminants within it. This means that they use a fan to push air through their extremely fine filter.
If you looked at the actual filter from either a HEPA or ULPA purifier, it would look a lot like folded paper. That’s because it is made out of paper—but not the same printer paper you buy at the office supply store. In fact, this “paper” isn’t made out of wood at all. It’s ultra-fine glass fibers!
If you were to look at this material under a microscope, you’d see that it isn’t a precisely woven net, but rather a mat of glass fibers overlapping and twisting around each other at random. This Velcro-like pattern is perfectly crafted to maximize contact with the air flowing through it.
This paper is carefully pressed, folded, cut, and sealed to create a path which air can get through, but most of the contaminants in it can’t. In fact, the fibers catch particles in four different ways—but more on that later.
Both HEPA and ULPA filters can filter particles smaller than a micron (that’s about four hundred-thousandths of an inch)! HEPA filters catch particles of 0.3 microns with 99.97% efficiency. ULPA filters need to be able to catch particles of 0.12 microns with 99.9995% efficiency.
Both filter sizes can catch most of the common contaminants in air, but each has its strengths and weaknesses, which we’ll get to in a moment.
Four Types of Filtration
More common types of filters, such as those used to make coffee, function very intuitively. Close-woven fibers work like a net to allow a fluid to pass through while catching particles within it. However, even though gasses like air use similar fluid dynamics to water, these intuitive processes aren’t the whole story.
HEPA and ULPA filters work at such a small scale that the forces we usually consider mean a lot less, and a different sort of filtration becomes possible.
These filters catch particles in four different ways:
- Diffusion (Brownian Motion): Air particles and the contaminants they carry are so small that they don’t move the way we might expect. Other than general direction determined by wind, these particles move quickly in random directions. These random movements bring contaminants into contact with the glass fibers of the filter, trapping them.
- Inertial Impaction: Much more intuitive, this is when a particle can’t keep up with air when it flows around the filter. This is similar to how water flows around a rock in a river, but a boat will run into it without intervention, even though it’s carried by the water.
- Interception: Think about that boat again. If it manages to turn almost enough, it won’t ram the rock head-on, but might scrape along the side. For particles in a HEPA filter, even scraping the fiber is enough to trap them, leaving the air unpolluted as it flows on.
- Electrostatic Attraction: Lots of particles have a small electrical charge. This magnetism works just like you’d think: it pulls the contaminant onto the filter where it sticks.
This combination of forces is a great combination for cleaning your air! Larger, heavier particles get caught by impaction and interception, while small particles are caught because of diffusion and electrostatic attraction.
This means that smaller particles aren’t always the hardest for your filter to catch!
In fact, the reason that HEPA filters are rated for particles at 0.3 microns in size isn’t because they won’t catch anything smaller. It’s because these particles between 0.1 and 0.3 microns are the hardest to trap. They’re too big to be affected much by Brownian motion and electrostatic attraction, but they’re small enough to go with the flow of the air and not get caught by the fibers.
Now, this doesn’t mean that the filter will catch everything else. Neither HEPA nor ULPA filters can be expected to stop many viruses (though both should be able to filter out bacteria, which are much larger).
Still, the fact that HEPA filters can catch well over 99.9% of particles this size is a testament to their extreme quality.
ULPA filters were specifically designed to combat this limitation. They’re rated almost down to 0.1 microns, where Brownian motion means there’s not much more such simple filters can do. This makes them more effective at catching the tough in-between particles, but that doesn’t necessarily mean they’re the better choice for everyone and everything.
HEPA vs ULPA: Major Differences
Both HEPA and ULPA filters catch microscopic particles and produce clean air. Since ULPA filters are rated to catch 99.9995% of particles 0.12 microns in size, are they just flat out better than HEPA’s 99.97% efficiency at 0.3 microns?
Not necessarily. While ULPA filters do produce cleaner air, HEPA filters have a few advantages that can make them the better (and even more effective) choice!
One major difference between the two filters is airflow. ULPA filters are so effective in part because they’re extremely dense. This is great for catching particles, but it also slows down air. This means it takes more energy to push less air through a filter.
Not only does this mean higher energy costs, but because less air is cycling, it means it takes longer for all the air in a room to get cleaned. By that time, a whole new slew of particles might be contaminating it. Because of this, HEPA filters often produce rooms with cleaner air, just because they work faster.
It’s not only energy costs that are higher with ULPA filters. Because of their more specialized design and the increase in filter material necessary to make the dense folds, ULPA filters can cost between 30-50% more than their HEPA counterparts.
Worse, ULPA filters generally have a shorter lifespan than HEPA filters. Not only does the fan have to work harder to blow air through, shortening its lifespan, but the filter catches more particles while having less space to clog up. It’s a vicious cycle that can give it a lifespan as low as half that of a HEPA filter.
With these, you pay more to run a more expensive piece of equipment that you have to replace more often. It can add up quickly. Although it produces a more well-filtered end product, the relatively slow turnover means that it’s often less effective at giving you a clean room of air.
A more relaxed HEPA filter is about 75% of the cost of an ULPA filter and can last up to twice as long. It moves air faster, and can leave you with a more sanitized space. Meanwhile, the fan pushing the air through can enjoy a more relaxed run and longer lifespan itself.
This doesn’t mean HEPA filters are always the better choice!
ULPA filters exist for a reason. Many specialized fields require clean rooms without the smallest contaminant. Precise electronics manufacturing (such as the production of semiconductors), certain biological laboratories, and some kinds of pollution cleanup require the super-clean air of an ULPA filter.
Even hospitals, however, often get by with HEPA filters. These are adept at catching the particles viruses hitch a ride on and can handle the bulk air cycling required by a large building. It’s really just the very specialized work that requires the precision of an ULPA filter.
Conclusion: No One Size Fits All
Make no mistake: both HEPA and ULPA filters are extremely powerful. Both types remove particles smaller than the human eye can see from the air, leaving it cleaner, safer, and healthier.
Without a reason to use an ULPA filter, a HEPA filter is usually the better bet. Because it cycles more air, it leaves fewer contaminants in the air in most cases. However, in cases where the smallest pollutant can ruin your work, it’s worth considering the mightier ULPA filter.
Thank you! We hope this article has helped you understand the differences between these two powerful filters. If you found what you were looking for, consider looking at some of our related content below.