What is a HEPA air scrubber?
A HEPA air scrubber is a heavy-duty air purifier that creates negative pressure. They filter out 99.97% of viruses, mold, dust, asbestos, lead, and other contaminants from the air.
Difference Between Regular Home Air Purifiers and HEPA Air Scrubbers
The only difference between HEPA air scrubbers and regular home air purifiers is that the air scrubbers are built for commercial and construction use.
They also have an extra port on the exit side that allows air to be ducted out. This process creates negative pressure.
All other aspects of the devices are exactly the same. This includes the HEPA filter, which removes 99.97% of particles.
Some HEPA air scrubbers, like other HEPA air filters, also have a carbon filter. This purifies the air at a molecular level by removing gases, Volatile Organic Compounds (VOCs), and even scents.
HEPA Air Scrubber vs. Air Purifier
Because they are built for commercial use, HEPA air scrubbers have a set up that is slightly different from typical home air purifiers.
First of all, they’re not nearly as pretty. Air scrubbers are built primarily for function.
(Quite frankly, they look like pieces of heavy duty construction equipment.)
Second, they have a an outlet to specifically pipe out air. This is creates negative pressure. Sometimes, these machines are also called a “negative air machines.”
The last major difference is that manufacturers of commercial HEPA air scrubbers typically do not care about sound levels or energy usage. Therefore, they may use a very loud, energy-intensive fan to move a lot of air very quickly.
Uses for HEPA Air Scrubbers
Hospitals and other places where people may need to quarantine from others can benefit from negative air machines.
The only way to properly quarantine is to keep air from leaking out of the room. You can create negative pressure in the room by blowing air out of the room with a fan. Then, you seal off the rest of the room to the best of your ability.
Since you cannot just vent toxic air out into any place, you have to filter it first. This is where the pre-filter, HEPA filter, and optional carbon filter come in to play.
The HEPA filter is really the main actor here, filtering air down to 0.3 µm (0.3 micrometers or 0.3 millionths of a meter) with up to 99.97% efficiency. Since all of the air that is sucked out of the room runs through the filter, it is safe to breathe.
What to Look For in a HEPA Air Scrubber
1. The Pre-Filter
The pre-filter in an air scrubber cheaply removes contaminants from the air before sending it through the more expensive HEPA filter.
Yes, it would be possible to simply make a HEPA filter and attach it to a fan. The only problem with this is the cost of replacing a HEPA filter when it gets clogged up with larger particulate matter.
So the cheaper way of doing it is to put something like a Merv 11-13 furnace filter in front of the HEPA filter. That way, air going into the HEPA filter is already very clean, making the HEPA filter last longer.
For example, here is a quick calculation using three readily available air purifier filter media sold on Amazon:
Cabiclean Round HEPA Air Filter: 140 square inches of surface area for $13.50 ($0.096/square inch)
Cabiclean Honeywell Replacement HEPA Filter: 398 square inches of surface area for $37 ($0.093/square inch).
Note that these are thicker than the round version, so they’re actually even cheaper than this.
MERV 13 Air Filters are 12x12x1 in a 6-pack for $43. This is 864 square inches of surface area for $40 ($0.050/square inch).
Compare prices:
MERV 13: $0.05 per square inch
Both HEPA filters: $0.09 per square inch
Even the super cheap HEPA filter off of Amazon is roughly twice the price of an equivalent MERV 13 filter.
When you look at these two types filters for filtration efficiency, the difference is actually quite small.
The MERV 13 filter will filter out over 90% of particulate matter between 3 µm and 10 µm, over 90% of particulate matter between 1 µm and 3 µm, and under 75% of particulate matter between 0.3 and 1 µm.
A HEPA filter is the equivalent of a Merv 17 filter, which filters 99% of particulate matter between 1 µm and 10 µm and 99.97% between .3 and 1 µm.
Theoretically, you could stack even more pre-filters together, including washable filters (which capture virtually nothing) and cheaper Merv filters, like a MERV 7 or MERV 8. The latter filters only capture the largest particles around 3 µm to 10 µm.
But, at some point, pre-filtering becomes excessive and the resulting pressure drop becomes too high for efficient air movement. Plus, the lower MERV filters are not that much cheaper than a quality MERV 11 or MERV 13 filter.
The best thing to do is to simply use a MERV 13 pre-filter with a HEPA filter.
2. The Air Filtration Media
When you get down to it, air filtration is really just about blowing air over a medium that removes particulates from the air. There are two effective medias used for doing this.
One common method of filtering air is a physical filter, such as a furnace filter or a HEPA filter.
Another is a physical media like activated carbon that adsorbs (yes, aDsorbs, not aBsorbs) molecules to its surface. The activated carbon removes molecular level contaminants (VOCs, paint fumes, smells, etc…) from pre-filtered air.
Most HEPA air scrubbers and home air purifiers have both a HEPA filter and activated carbon.
Things to Avoid in a HEPA Air Scrubber
1. HEPA vs Patented Super-Particle Molecular Fission Particulate Destruction (SPMFPD™)
Look, most of the “ultra-secret technology” out there is simply a scam.
It’s either:
A) A company using HEPA filters and activated carbon to do the filtration work, then giving it a fancy name (like “True Hepa”) or…
B) Some made up nonsense that marketers are using to make you think they have some special secret new patented product that works better than anything else scientists have come up with.
But ask a nuclear engineer what they use to filter out nuclear waste and protect people of the surrounding countryside from inhaled nuclear particles… They’ll tell you it’s simply a HEPA filter.
Ask your doctor what they use to keep the surgical suite clean of contaminants. Again, it’s a HEPA filter, and maybe some carbon filters added on top of that for “molecular filtration” (particles too small to be picked up by physical media). Then maybe they add a bunch of UV light to kill any bacteria that ends up on surfaces.
Think about this from a cynical perspective. You can’t mark up a sub-standard $50 air purifier to over $800 if you’re simply blowing air over a filter media like 20 other companies out there are doing.
You have to convince potential customers that you’re destroying particles and killing viruses on a nano-scale level with your patented super process based on advanced particle physics. All the better if the wording is so complicated that nobody understands what the heck you’re talking about.
Bottom line? HEPA filters are just as good as any expensive products claiming to use newer technology.
2. Avoid Proprietary Filters
Story Time. I know a guy that started a now-defunct air purifier company about two years ago.
One day he said to me, “I’ve run all the projections and done spreadsheets for hours and hours and hours. The real money is made in selling people filters after the initial unit is sold.”
The product he was selling was $800. Was is $800 quality?
No. It was made cheaply in China. But given the size, the shipping and the cost of manufacturing, he actually just broke even on the initial air purifier purchases.
Where he made money is on the back-end when customers had to re-buy his specific air filter.
Over and over and over.
This gets expensive quickly.
Most people don’t think about the cost of filters because it’s some thing on the back-end. It’s like miles per gallon in your car. At first, that big old SUV or work truck is really fun to drive around, but over time you get sick of throwing $80 at the gas tank every three or four days.
Now imagine doing that with a consumable used for work, like an air filter. The difference between a $10 replacement air filter that you can buy at any home improvement store or local Wal-Mart and a proprietary $20 air filter that you can only get from the one company you bought the unit from adds up over time.
Imagine going through three of those filters in a two-day job where construction dust is blanketing the air in a thick fog.
Now multiply that by years of home remodeling or hospital filtration and you’re looking at thousands of dollars just in filters.
Given the initial unit is around $600-$800 and would last at least five years, the difference between using proprietary filters and off-the-shelf filters could easily double or triple the total cost of filtration.
For that reason it makes a lot of sense (even if you have to spend a few hundred extra dollars) to buy a unit that will except standard size filters.
This is more common for pre-filters since furnace filters come in a variety of standard sizes like 12 x 12 and 20 x 20, but it is unfortunately very rare for HEPA filters. These are usually sold only for a specific model air purifier (eg “Replacement HEPA Filters for Honeywell Tower Unit” or “Round HEPA Filters for Dyson Filtering Fan”).
Activated Carbon (The Optional Extra)
Now let’s talk about molecular filtration. The most common medium for this is activated carbon.
On a molecular level, it’s simply a substance with lots of tiny crevices that molecules can stick to the inside of. This includes everything from paint fumes to volatile organic compounds (VOCs) to molecules that can cause smells.
Yes, you read that right. You can literally filter farts out of the air.
Activated carbon is not a 100% necessary in all cases. Demolition or mold mediation may not require activated carbon since a pre-filter and a HEPA filter will remove those particles from the air.
Likewise, filtering viruses from the air probably doesn’t require activated carbon either.
(Although for the slight extra cost of adding what is essentially overpriced charcoal to your air purifier, I would insist on activated carbon filters if I were running a hospital.)
When to Use Activated Charcoal
If you’re doing something that will produce fumes or gases, however, activated carbon is absolutely necessary.
A common example is painting.
All the HEPA filters in the world will not filter paint fumes. They will filter paint aerosol, but they won’t filter the toxic fumes given off as the paint dries.
In this case, activated carbon would be necessary for filtering the paint fumes. (This is why respirators for painting have those big clunky filters; there’s activated carbon in them.)
Keep in mind that activated carbon does fill up on a molecular level over time. Eventually, it will need to be replaced.
Luckily, activated carbon is popular for filtering aquarium water, so you can buy it in bulk relatively cheaply. Just make sure you can refill the activated carbon in your air purifier.
Amount of Activated Charcoal Needed
Keep in mind that the amount of activated carbon is very important. Air passing over the carbon bed has to be in touch with the carbon for about 0.07 seconds to remove odors.
For most flow rates, this means about 1 inch of an activated carbon filter media is required.
You’ll often see thin filters or even tiny dustings of activated carbon on top of a HEPA filter. This seems more like a marketing ploy then a legitimate strategy for filtering the air.
If you want to see what real activated carbon filtration looks like, look into ventilation systems for grow tents or industrial carbon filters. These are seriously thick filters with plenty of weight to them.
Are Air Scrubbers Worth It?
Air scrubbers are the industrial versions of home air purifiers. They use pre-filters, HEPA filters, and activated charcoal to remove 99.7% of pollutants and odors from the air.
HEPA air scrubbers are necessary for maintaining a clean environment during painting, construction, and even manufacturing. They are also important for keeping medical facilities clean.
To save money on a HEPA air scrubber in the long-run, get a unit that is compatible with generic pre-filters, activated carbon filters, and (if possible) HEPA filters.
This page last updated July 20, 2021