Vacuum boxes are full of filtration words, and they sound like one promise in different fonts. They aren't. One is a U.S. government definition, two are filter classes, several are brand names and one is an independent certification.
Here is what each term promises and what it leaves out. For model-by-model picks, see our allergy vacuum guide.
Key takeaways
- HEPA rates a filter at a 0.3-micrometer test size. It says nothing about the vacuum around the filter.
- A filter only cleans the air that reaches it, so seals and the bag matter as much as the filter's label.
- Miele's AirClean names describe a filter's job. Only HEPA AirClean carries a filter class.
- SEBO's S-class is a different standard from HEPA, and "hospital-grade" is SEBO's heading for a tightly sealed machine.
- The asthma & allergy friendly® mark tests a whole vacuum in an independent lab, so check that the exact model is on the certified list.
Vacuum filtration terms at a glance
| Term | What it promises | What it doesn't tell you | Who should care |
|---|---|---|---|
| HEPA (U.S. Department of Energy definition) | At least 99.97% efficiency against 0.3-micrometer test particles | Whether air leaks around the filter | Anyone comparing filters |
| HEPA class 13 (Miele HEPA AirClean) | A class under DIN EN 1822, a separate filter standard; Miele quotes 99.95% | A result under the DOE definition | Miele owners choosing an exhaust filter |
| S-class (SEBO) | Per SEBO, more than 99.9% of particles down to 0.3 microns | Where the filter sits in the machine | SEBO shoppers weighing it against HEPA |
| Sealed system or tightly sealed casing | Air leaves through the filters, not the seams | A shared test; each maker uses its own words | Everyone, especially anyone buying HEPA |
| "Hospital-grade" filtration (SEBO) | SEBO's heading for tight seals and filtration tested while running | A filter class or number | Shoppers comparing marketing words |
| AirClean and AirClean Plus (Miele) | Everyday filtration; Plus is for "particularly clean room air" | A HEPA class | Miele owners without odor or fine-dust concerns |
| Active AirClean (Miele) | Active charcoal for odors | A HEPA rating | Households with pets or smokers |
| asthma & allergy friendly® | Independent lab tests of the whole vacuum | Anything about uncertified models | Anyone who wants third-party testing |
| Three-layer or HyClean bag | Holds the dirt and closes for disposal | That a generic bag does the same | Everyone with a bagged vacuum |
What does HEPA actually mean?
HEPA stands for high efficiency particulate air, a filter type as officially defined by the U.S. Department of Energy, the EPA notes. The DOE's standard, written for HEPA filters used in DOE nuclear facilities, says a HEPA filter "shall exhibit a minimum efficiency of 99.97% when tested with an aerosol of 0.3 micrometer diameter."
Why 0.3? The EPA calls it the worst case, the most penetrating particle size, and says particles larger or smaller are trapped with even higher efficiency. So 99.97% is a floor, measured where a filter is weakest.
Notice what the definition covers: a filter, on its own. Nothing about the bag in front of it, the gaskets around it or the vacuum's housing. Even the EPA says such a filter can "theoretically" remove at least 99.97% of particles that size. In a vacuum, that applies only to the air that actually passes through it.
Is a HEPA filter the same as a sealed system?
No. A filter rating tells you how well the filter catches particles. Sealing tells you whether the dirty air reaches the filter at all.
SEBO puts it plainly: dirty air "can only be filtered completely if it does not escape into the room through seams or seals in the machine." SEBO also argues that many high-filtration claims quote a filter material's laboratory specification rather than the vacuum's filtration while operating. On the AUTOMATIC X7 and X8, SEBO places the filters in a tightly sealed casing that prevents dirty air from escaping through its seams.
Miele describes filtration as a system. Its instructions for GN-bag canisters say the Miele Filtration System consists of 3 accessories: the FilterBag, a motor protection filter and the exhaust filter. On a HyClean bag sheet, Miele quotes 99.99% "thanks to Miele AirClean system," footnoted to IEC 62885-2, an international standard for measuring the performance of household dry vacuum cleaners. That is a whole-machine figure, not a filter class.
So compare like with like: a filter rating against a filter rating, a machine figure against a machine figure.
What do Miele's AirClean filter names mean?
Miele sells several filters under the AirClean name, and the word in front tells you the job. Miele's U.S. fact sheets put it this way:
- AirClean: "Effective filtration for everyday needs."
- AirClean Plus: "effective filtration for particularly clean room air."
- Active AirClean: made with active charcoal, which Miele calls ideal for households with pets or smokers.
- HEPA AirClean: Miele says it "safely traps fine dust and allergens" and rates it HEPA class 13 under DIN EN 1822/2011, quoting 99.95%. DIN EN 1822 is a standard for classifying and testing high efficiency air filters.
The AirClean, AirClean Plus and Active AirClean sheets each list "Safely seals in the dust," which is Miele's containment wording, not a particle rating. Only the HEPA AirClean sheet gives a filter class and a percentage. And Miele's 99.95% and the DOE's 99.97% come from different standards, so don't treat the two numbers as interchangeable.
Which size fits your machine is a separate question, and our Miele filter guide covers it.
What do SEBO's S-class and "hospital-grade" mean?
S-class is SEBO's standard filtration. SEBO says the S stands for Schwebstoff, or airborne particles, and that the S-class standard requires filters to absorb greater than 99.9% of particles down to 0.3 microns in diameter.
Why not HEPA everywhere? SEBO says S-class filters have a relatively open texture that allows smoother airflow for better suction, a longer life and a lower price than HEPA filters. Its optional HEPA microfilters remove a minimum of 99.97% of particles down to 0.3 microns but clog sooner, so SEBO sells them along with three-layer bags that filter the air first.
S-class names a grade, not a position. A pre-motor filter catches dust before the air passes over the motor to cool it; an exhaust filter cleans the air on its way out. The AIRBELT K has an S-class pre-motor microfilter and an optional HEPA pre-motor microfilter. On the AIRBELT D, the S-class filter is the exhaust microfilter. Our allergy guide shows which SEBO families take a HEPA option.
"Hospital-grade" is SEBO wording too. The heading "Tightly Sealed Hospital-grade Filtration" sits over text about seals: SEBO says all its vacuums have tight seals throughout and that their filtration effectiveness is tested while they operate. No separate class or number comes with the phrase, so read it as a description of a sealed machine.
Three products we carry, described in their makers' filtration terms:
Miele SF-HA 50 HEPA AirCleanGuard S1, M1 and L1 owners who want HEPA class 13.$64.00View product
SEBO AIRBELT K3 PremiumCanister buyers who want S-class now and a HEPA option.$949.00View this model
SEBO AUTOMATIC X7 PremiumUpright buyers who want an S-class pre-motor filter in a sealed casing.$1,149.00View this model
What does the asthma & allergy friendly® mark test?
Unlike the other terms here, this mark is awarded by an outside program after testing, not claimed by the maker. The Asthma & Allergy Friendly® Certification Program is a partnership of the Asthma and Allergy Foundation of America (AAFA) and Allergy Standards Limited (ASL). It says every product is tested by an accredited, independent lab, not the manufacturer, and is re-tested to keep the mark. For vacuums, the program lists these tests:
- Allergen pickup: at least 90% of allergens removed from both a floor covering and a crevice.
- Airborne particles: below the program's thresholds, both while vacuuming and when emptying the dust receptacle.
- Seals: checked so dust can't bypass the filter.
- Loaded performance: less than a 10% loss of suction with a full dust receptacle.
AAFA's own summary also counts allergens released when changing the bag or emptying the canister. That makes it the broadest test on this list. But it applies only to the products the program certifies, so check the program's product finder for the exact model before relying on the mark. A missing mark means a model wasn't certified, not that it failed a test. Certification isn't medical advice either; if someone at home has asthma or allergies, follow their doctor's plan.
What does the bag contribute to filtration?
On a bagged vacuum, the bag is the first filter. SEBO says its top-fill, three-layer bags hold virtually all dirt captured by the vacuum, which improves the effectiveness and useful life of the microfilters, and can be sealed when full so no dust escapes during removal and disposal.
Miele's instructions for GN-bag canisters say FilterBags with the Miele logo are not made from paper or paper-based materials, and that the bag's flap closes automatically when you raise the dust compartment lid. Miele says its AirClean 3D Efficiency FJM bags filter more than 99.9% of all dust particles.
Both makers tie genuine supplies to the warranty. The same Miele instructions say faults caused by accessories without the Miele logo on the packaging aren't covered, and tell owners not to re-use FilterBags. SEBO says washing filters, reusing bags or using counterfeit parts may invalidate its warranty; our filter-washing guide has more.
So before paying for a filter upgrade, get the basics right: the genuine bag for your model, changed on time, with every filter seated where it belongs. Our guides to Miele bags and SEBO bags by part number match the bag to the machine.
Vacuum filtration questions
Is a HEPA filter the same as a HEPA vacuum?
No. HEPA describes the filter. The vacuum still has to send the air through that filter instead of letting it leak past seams.
Is S-class as good as HEPA?
They are different standards. SEBO says S-class filters must absorb more than 99.9% of particles down to 0.3 microns and that its HEPA microfilters remove at least 99.97%, but S-class filters allow smoother airflow and last longer.
Is Miele's HEPA AirClean filter true HEPA?
Miele rates it HEPA class 13 under DIN EN 1822 and quotes 99.95%. The U.S. Department of Energy definition uses 99.97% at 0.3 micrometers. They are different standards, so compare each filter against the one its maker names.
Does the vacuum bag affect filtration?
Yes. SEBO says its three-layer bags hold virtually all the dirt, which helps the filters behind them work and last, and Miele says its FilterBags close with a flap when you open the lid. Use the genuine bag for your model.
Keep reading: Best vacuum for allergies and asthma · Miele filters: check fit before choosing HEPA · Can you wash your vacuum filter?
Sources: U.S. EPA, What is a HEPA filter?; U.S. Department of Energy, DOE-STD-3020-2015; IEC, IEC 62885-2:2021; DIN Media, DIN EN 1822-1:2019-10; Miele U.S. fact sheets: SF-SAC 20/30 AirClean, SF-AP 50-1 AirClean Plus, SF-AA 50-1 Active AirClean, SF-HA 50-1 HEPA AirClean, AirClean 3D Efficiency FJM bags, CO Allergy XL HyClean Pure; Miele HS12 canister operating instructions; SEBO filtration system, standard features, FAQ, AUTOMATIC X7 and X8, AIRBELT K, AIRBELT D, 2024 catalog; Asthma & Allergy Friendly® Certification Program: Why certified?, vacuum criteria, product finder; AAFA, Not All Vacuums Are Equal (checked November 2026).
