What is the rating of the HEPA filter?

Thus, it is most useful to think about a HEPA filter rating as an application check-off list of four bullet points that must be combined:

• The efficiency rating itself
• The particle size for which the efficiency is rated
• The classification standard (or letter) such as EN 1822, ISO 29463, US MIL-STD-282, IEST-RP-CC001, ASHRAE 52.2 MERV that defines the HEPA filter class
• The description of intended operating performance limits — rated airflow, initial and final pressure drop, and temperature and humidity requirements

The first three points specify filtration claims, while the fourth defines how well the filter will work in practice. The information given above is in the form of a percentage; however, it is actually specifying a complete coordinate system. The percentage refers to the effectiveness of the media in capturing particles whereas the particle size refers to the relative measurement at which this number holds true.

The standard refers to the specific test being used to derive this number and the acceptance criteria being applied. Finally, the limits specify the airflow, pressure drop, temperature, and humidity under which the filter can be operated without losing its effectiveness based on the reported number.

When the four items above are looked at together, it is possible to compare filters more effectively and accurately. On the contrary, looking only at an individual value can lead to incorrect conclusions about a product.

A catalogue that references "99.99%" does not provide adequate information in the technical sense to provide a valid HEPA filter rating, unless it includes both the particle size and the test standard behind the HEPA filter rating.

In contrast, a catalogue that makes the following claims: H13 under EN 1822, minimum classification efficiency at MPPS, rated airflow of 2500 m³/h, initial resistance of ≤200 Pa, final resistance value of between 400–600 Pa, maximum operating temperature of 70°C, and maximum operating humidity of 80%, offers complete specifications which can be utilized for design.

One thing to note about the latter two values is that they refer to product operational limits from the catalogue and are not included as part of the formal efficiency classification.

The importance of the four-part HEPA filter rating framework is compounded by the fact that the cleanroom industry mixes standard approaches. For example, projects in Europe often rely on the EN 1822 HEPA classification and ISO 29463 as the default standards for cleanroom construction. In the United States, however, projects often utilize MIL-STD-282 and IEST-RP-CC001.

Additionally, HVAC specifications may utilize the ASHRAE Standard 52.2 (which also utilises the MERV 17-20 scale). Because each standard uses different test aerosols, particle sizes, and acceptability criteria, it becomes critically important to differentiate between these HEPA filter rating frameworks when making decisions on where to use each specific HEPA filter model.

Just because two filters seem to have the same HEPA filter rating on paper does not mean that they will have equal real performance. In fact, two filters can have the same rating number but have entirely different performance due to different test methods.

Figure 1: Illustration of four-part specification checklist for HEPA filter rating: efficiency number, particle size measured, classification standard and class letter, and acceptable operating performance and conditions.

Introduction: Decoding the HEPA Filter Rating

When a facility engineer, contractor, or procurement team asks about the rating of a HEPA filter, the answer they need is rarely just a percentage. The percentage is the headline, but the full specification is a coordinate system. The HEPA filter efficiency number tells you how well the media captures particles. The particle size tells you at which point in the aerosol spectrum that number applies.

The standard tells you which test method produced the number and which acceptance criteria were applied. The operating limits tell you the airflow, pressure drop, temperature and humidity under which the filter can be used without losing its rated performance.

Read those four items together and you can compare two filters meaningfully. Read only one of them and you can be misled. A catalogue entry that says "99.99%" without a particle size or a standard is not a HEPA filter rating in the technical sense.

A catalogue entry that says "H13 under EN 1822, minimum classification efficiency at MPPS, rated airflow 2,500 m³/h, initial resistance ≤200 Pa, final resistance 400–600 Pa, maximum temperature 70°C, maximum humidity 80%" is a complete specification that can be designed around. Note that the last two values are product operating limits from the catalogue, not part of the formal efficiency classification.

The four-part framework matters because the cleanroom industry mixes standards. European projects default to the EN 1822 HEPA classification and ISO 29463. US projects frequently reference MIL-STD-282 or IEST-RP-CC001 to justify a HEPA filter rating. HVAC specifications may use ASHRAE Standard 52.2 and its MERV 17-20 scale. Each framework uses a different test aerosol, a different target particle size, and a different acceptance criterion.

Two filters with the same real performance can appear on paper to have different ratings if the numbers were produced under different standards. Two filters with the same paper number can have very different real performance if the underlying test methods differed.

Understanding Filtration Standards: US vs. EN 1822 vs. ISO

There are three major standards families upon which a HEPA filter rating could be established: the EN 1822 HEPA classes, ISO 29463, and the US system that includes MIL-STD-282 and IEST-RP-CC001. Each family consists of specific aerosol, particle size target, and reporting methods that are unique to it. Therefore, understanding the standard that generated a HEPA filter rating is just as important as knowing the number itself.

The Shift from 0.3 µm to MPPS

The use of 0.3 µm particle size as a reference particle size has been a standard used in the legacy DOP based HEPA filter testing method in the US. Use of this reference particle size was made after testing showed that it represents the hardest particle size to test using typical glass fibre HEPA media.

The previous definition of HEPA, i.e. a minimum of 99.97% efficiency at a 0.3 µm particle size was established based on this testing and remains a widely utilized definition to date. The EN 1822 and ISO 29463 methods classify filter types based on the so-called most penetrating particle size (MPPS) [3][5].

The most penetrating particle size (MPPS) is the size of particle for which the collection efficiency of the tested filter is the lowest according to given test conditions. The MPPS depends on the type of filter medium used and the air flow conditions. The MPPS of many glass fiber HEPA filters is in the submicron region, generally around 0.1–0.2 µm.

The exact MPPS should not be considered as a universal number for all the products, though. The value of MPPS may be different for synthetic and PTFE filters in comparison with the glass fiber ones.

The relationship between a HEPA filter rating by 0.3 µm particle size and a rating according to MPPS values is therefore not direct. The two ways of assessing HEPA filter efficiency reference two different particle sizes and employ different acceptance criteria, which is why a single HEPA filter class number is not portable between standards.

Filter with 99.97% efficiency rating by 0.3 µm particle may or not have this efficiency at MPPS conditions. H13-classified filter according to the EN 1822 standard may not have the same efficiency value at 0.3 µm conditions according to American standards. Therefore, the two numbers cannot be converted by means of formula; they should not be treated as proofs of one another.

Figure 2: Penetration versus particle size curve showing the legacy 0.3 µm reference point and the MPPS band for glass-fibre media, illustrating why the two reference points are not equivalent and cannot be converted by a simple formula.

Mapping the Global Landscape

The major standards' frameworks are considered in this paragraph. The US MIL-STD-282, which demonstrates the use of a DOP aerosol of 99.97% minimum efficiency at 0.3 µm for HEPA testing [9], is simply one US methodology for establishing a HEPA filter rating.

The IEST-RP-CC001 sets forth the recommended procedure for HEPA and ULPA filters in the US; it provides guidance for HEPA filter class performance and construction [6]. the EN 1822 HEPA classification is the European standard for classifying filters as EPA (E10 through E12), HEPA (H13 through H14) and ULPA (U15 through U17), and it uses MPPS testing for classification purposes.

It has several sections outlining classification and marking, filter element testing methods, and filter media testing methods [3][4]. ISO 29463 provides a framework for classification and testing; it has its own terminology and standards in comparison with the EN 1822 HEPA classification. Users should not assume equivalency but must specify the appropriate standard, section, edition, and class number for testing.

ASHRAE Standard 52.2 provides a standard for HVAC filter testing and rating using ratings based on MERV; it does not generate any HEPA filter class or ULPA classification, using particle size bands instead [8]. EN 779 is a general classification method for HVAC filters that has been updated by ISO 16890. However, the use of F5 to F9 designations may still be useful [7].

Finally, one major point buyers need to keep in mind is that MERV and EN 1822 HEPA classes cannot be assumed to be directly interchangeable. The MERV classification is based on the efficiency of a particle-size class based on test method ASHRAE 52.2 whereas the EN 1822 HEPA and ULPA classes have a different basis of testing and passing criteria based on maximum particle size efficiency.

The MERV classification alone does not determine compliance according to the EN 1822 H13, H14 or U15–U17 standards. Likewise, compliance according to EN 1822 H13 or H14 does not automatically mean that the MERV rating is fulfilled when specified in a specification.

Figure 3: Mapping ladder of EN 1822, ISO 29463, US/DOE naming and ASHRAE MERV 17–20, showing the applicable standard and test basis for each and noting that MERV and EN 1822 are not directly convertible.

Master Rating Comparison Table

Presented on the table below is a summary of the basic classes and their basis of test. The test standard, class, basis of testing and typical application for all classes are indicated for each row in the table. The room class references in this table are used for illustrative purposes only; the final filter selection depends on system design and qualification requirements.

Table 1: HEPA filter rating classes across EN 1822, ISO 29463, US/DOE and MERV.

Please note: the EN 1822 figures should be checked against the specific edition of EN 1822-1 that is being referenced. The ISO 29463 class labels should be checked against the applicable edition of ISO 29463-1. The US MIL-STD-282 figure is based on that historical test specification. The MERV figures are derived from ASHRAE 52.2. MERV classification works from ASHRAE 52.2 test method, and EN 1822 classification does not directly correlate with MERV classification.

Table 2 shows the mapping of the three Deiiang product families against the rating framework. These figures are Deiiang catalog data and pertain to the specified product families/models; they do not have universal class values.

Table 2: Deiiang product families and their rated classes.

Notes on the Deiiang efficiency figures: the 0.3 µm values for H13 and H14 are indexed data concerning the performance of products at a fixed particle size — separate from the EN 1822 classification limit established according to the Most Penetrating Particle Size (MPPS). Thus, they do not offer proof of being classified according to EN 1822 specification on their own.

The proof in classifying a specific design is the EN 1822 test report obtained from the respective facility of the model, which is additionally validated with a unique test result done per unit. As for the figures to identify the U-series, the information is also gathered from the catalog and thus does not follow the definitions given under EN 1822 since it highlights MPPS test procedure.

Deiiang Product Families: Engineering Performance

The entire Deiiang line of products includes major HEPA filter groups commonly used in cleanroom and HVAC systems. The two main families of HEPA filters are Combined High-Efficiency Filter and DOP Integrated Filter, both made in H13 HEPA filter and H14 HEPA filter grade under EN 1822 specifications. The other family being Super High Efficiency baffle filter extends into U15–U17 grades for critical applications.

Combined High Efficiency Filters (H13/H14)

Combined High-Efficiency Filters are designed to be used at last stage filtration process in air conditioning units, high air volume purifiers. The filter makes use of ultra fine glass fiber filter material without separators and where EVA hot melt thermoplastic spacers are used to keep the pleats evenly spaced apart. The media pack is glued to an ABS frame and with two-component PU sealant.

The front of the filter is fitted with diamond mesh to protect against debris. Gaskets can be fitted with EVA or neoprene depending on the customer choice.

This family of filters has an efficiency rating of 99.97–99.99% at 0.3 µm for the H13 range and 99.995–99.999% at 0.3 µm for the H14 category. These filters have a maximum operating temperature of 70°C, and a maximum relative humidity of 80%. They can hold about 1,200 g of dust capacity in the 2,500 m³/h model.

As noted in the catalogue, there is thorough testing conducted for each filter before shipment, and customer should check with Deiiang about the classification report or specific documentation available for that particular model, as well as any orders made.

The size and performance specifications can be seen in the following model specifications table. These values are for the specified models operating at rated airflow.

Figure 4: Deiiang Combined H13/H14 high-efficiency filter product photo shows the ABS frame, separator-less pleat pack, and a diamond mesh protective screen.

DOP Integrated Filters (Compact Design)

The DOP Integrated Filter addresses the same H13 and H14 classes like the Combined family but in a compact box structure designed to be used in cleanrooms in which the height of the civil works is limited.

The appliance consists of a built-in air inlet pipeline having a diameter of 250 mm, 300 mm, or 350 mm, and an air flow adjustment valve on the air inlet side, and a DOP tube test port that is covered with a rubber cap on the air outlet side. The exterior case of the appliance has been fitted with the PEF insulating foam.

The media used is ultrafine glass-fiber paper which has been sealed with PU two-component sealing material, and has an aluminum folding or galvanized frame, and an EVA hot melt separator.

The catalog efficiency ratings of this model are exactly the same as the ratings of the combined family viz. H13 filters have efficiency rating of 99.97–99.99% at 0.3 microns, and H14 filters have an efficiency rating of 99.995–99.999% at 0.3 microns, with a maximum operation temperature of 70 degrees centigrade and maximum R.H. of 80%.

The catalog sizes and performance data are given below:

The existing DOP tube test port is the major differentiating appliance feature in the family. This capability allows leak testing of the installed filter on-site without having to remove it from the air handling unit, which is particularly useful for operations that cannot afford to halt production in order to test the filter.

Figure 5: Deiiang DOP Integrated box filter showing air inlet pipe, adjustable valve, and DOP testing port.

Advanced Filtration: ULPA Grades (U15-U17)

ULPA grades takes the ULPA filter rating system a step beyond the HEPA filter classes, and is quoted separately as a ULPA filter rating. Under the EN 1822 HEPA and ULPA framework, ULPA classes consist of U15, U16, and U17 [3] which are used in semiconductor fabrication, super LSI production, and ultra-clean laboratories that require exceeding contamination-control capabilities than those delivered by H14 HEPA filter units.

Semiconductor and Ultra-Clean Lab Applications

The Deiiang Super High Efficiency Baffle-Free Filter is designed for use in semiconductor fabrication, super-LSI production, and ultra-clean laboratories. It contains US HV ultrafine glass-fibre paper with a plastic thermoplastic spacer, an anodized external frame, and a protective diamond mesh. As per the Deiiang catalogue, the performance of U-series is stated with regard to a particular particle size of 0.12 µm as:

• U15: 99.999–99.9995% at 0.12 µm (data from the catalogue)
• U16: 99.9999–99.99995% at 0.12 µm (data from the catalogue)
• U17: 99.9999–99.999995% at 0.12 µm (data from the catalogue)

The values mentioned above are the catalogue performance values from the Deiiang catalogue at the specific size of particles. These values are NOT definitions of EN 1822 U-class, which has been derived through a different MPPS test procedure. Relevant EN 1822 test results, applicable MPPS and integral/local efficiency details must be requested by the buyers before classifying these products under EN 1822 classifications.

If these records are not available for checking, the user should describe these products as "catalogue-rated at the stated 0.12 µm efficiency" instead of saying that they are EN 1822 U15/U16/U17 classified.

Moreover, these filters cannot be directly replaced by H13 HEPA filter or H14 units, which are used in general-purpose cleanroom applications. They are specified as per the contamination-control strategy followed by a user and only when the system is designed in such a way so as to meet the specific airflow and pressure drop requirements for ULPA product use.

Figure 6: ULPA U15–U17 efficiency progression chart at 0.12 µm, showing the values stated in the Deiiang catalogue for the Super High Efficiency Baffle-Free Filter family.

Technical Specifications

The technical specifications and performance information relative to the catalogue of the Super High Efficiency Baffle-Free Filter are:

It should be noted that the basis for classification for these products is 0.12 μm while the H13 HEPA filter and H14 HEPA filter catalogue figures use a basis of 0.3 μm. The numbers are therefore not directly comparable.

Resolving Common Industry Confusions

There are three areas that cause misconceptions in the procurement of HEPA filters. The first deals with the phrase "true HEPA" and "HEPA-type". The second is the understanding that MERV and EN 1822 classifications are equivalent. The third is the belief that an independent catalogue rating ensures performance in the practical sense.

"True HEPA" vs. "HEPA-type"

The True HEPA term is an expression of marketing rather than a term used in the EN 1822 HEPA classification or any other classification of the same type. The term sometimes refers to a filter that genuinely meets the US HEPA benchmark of 99.97% at 0.3 µm or the equivalent classification under EN 1822.

The phrase "HEPA-type" as well as "HEPA-like" describes other products which may look like, or be made similar to HEPA filters but that do not meet the official standard of HEPA classification. The true HEPA rating phrase, therefore, is not a class name and should not be treated as one.

As far as cleanrooms or regulated applications are concerned, rather than finding out whether filters are "true HEPA", the more sensible question is to ask what law and class were used to test the filters and what documents were issued to back this claim.

For example, if a filter has passed tests per the EN 1822 H13 category with a specific scan report available, it can accurately be claimed as a verifiable HEPA filter class. However, if the filter is described as being "true HEPA" based on claims made without the supporting documentation, it is thus classified as unverified.

Any time the phrases above are seen, please make sure to ask what model they carry, what law and edition are being used, what class is being classified within, what the testing standards were, what evidence is made to support the model classification and, if needed in the facility's qualification process, what the individual unit classification test result is.

Remember, the classification report issued from the factory and the scan report from an individual model are not the same and the facility requiring traceability to satisfy compliance needs should request both.

Figure 7: Comparison chart showing True HEPA marketing language, HEPA-type claims, and the ASHRAE MERV rating range side by side, with the applicable standard and test basis marked for each.

MERV 17-20 and the Myth of Interchangeability

MERV 17 through MERV 20 and the EN 1822 HEPA classification criteria are distinctly different documents. A MERV 17 rating. MERV ratings do not provide a basis for compliance with any HEPA or ULPA class.

The two rating systems differ in terms of size ranges, test methods, and acceptance criteria, with no recognised means of conversion from MERV to any HEPA filter class under the EN 1822 HEPA classification, that is, one cannot equate any MERV 17, 18, 19, or 20 rating to H13, H14, or U15–U17.

MERV and EN 1822 classifications must therefore be looked at as an entirely different rating system rather than as two dialects of the same language and hence a specification calling for a filter rated by an EN class cannot be substituted by a MERV filter rating. Similarly a specification requiring a MERV filter cannot be substituted by an EN class and vice versa.

Examples of common specification errors on the part of manufacturers. Comparing a 0.3 micron figure from a catalogue against the MPPS-based class threshold as though the two are comparable. Using a MERV rating as though it represents an EN HEPA or ULPA class. Quoting the pressure drop figure without also providing the air flow rate at which it occurs.

Using a family or catalogue rating rather than the rating applicable to a specific model. Confusing an in-plant classification test using a filter with a classification test on an installed filter. Using the iso class of a room rather than the classification of the filter required by the design.

The Critical Role of Pre-filtration

A HEPA filter rating provides information regarding the initial capabilities of the filter but does not indicate the filter's life expectancy with a particular particle load. The amount of dust reaching the HEPA filter is determined by the upstream pre-filtration.

Extending HEPA Service Life

Deiiang's F5–F9 bag filters are classified by the old EU standard EN 779 [7]. The catalog efficiency ratings for grades F5 to F9 for 0.5 μm are: F5 = 45%, F6 = 65%, F7 = 85%, F8 = 90%, and F9 = 95%. These ratings are applicable on the old EU EN 779 technique and are not interchangeable to ISO 16890, which may be a requirement for new designs of general ventilation pre-filters.

A common catalog example is the six-bag 592 × 592 × 381 mm component rated for 2,050 m³/h and has an area of filter of 3.18 m². Initial pressure drop is below 50 Pa for F5 and less than 100 Pa for F8 whereas the final pressure drop for the filter is 250–400 Pa. The fiberglass filter can work under 150°C while the synthetic filter can work under 80°C. These filters are pre-filters and not HEPA filters.

The design objective of pre-filtration is to minimize the amount of the upstream particle load prior to entering the HEPA filter, which could augment the time taken by differential pressure rise by the HEPA filter.

How far the HEPA filter utilization is able to be extended will depend on the amount of dust present in the ambiances, the flow rate, the maintenance, and replacement practices, as well as the dust holding ability of HEPA itself. There is no universal lifespan extension determined solely from the efficiency class of the pre-filter. The appropriate pre-filter class is determined by the ambient load of the site and its previously determined maintenance plan.

Figure 8: Multi-stage filtration diagram showing an F5–F9 pre-filter stage upstream of an H13 or H14 HEPA stage, with airflow direction and differential pressure monitoring points.

The Importance of Per-Unit Testing

A catalog rating indicates the product family. It does not tell the performance of an individual filter. Two filters from the same product family may have different efficiencies because one of them has a media defect, a seal gap, or has suffered some damage regardless of both filters being manufactured according to the same design. Therefore, the value of per-unit testing is emphasized for cleanrooms.

Why Catalogue Ratings Are Only the Baseline

The HEPA filter class rating is determined by the results of the testing. The test defines the numbers and their meaning. According to EN 1822, the high class's classification test accomplishes a scan of the filter surface ensuring the local efficiency is adequate for the applicable class and not just that the average efficiency is acceptable.

A filter can pass the overall efficiency test but have a pinhole or seal gap in a local section and cause product leakage into the cleanroom.

The catalog indicates the performance to be expected from the design while the individual test report bracket accounts for the performance that has actually been recorded from the particular individual filter. In a regulated cleanroom, it is the second number that is important.

The Deiiang Commitment: DOP and Scan Testing

According to the information provided by Deiiang, the products will undergo strict testing before they are shipped. It is the responsibility of the facility to confirm the specific test method, aerosol, acceptance criteria, and documentation. If there is a need for per-unit scan testing, the facility should include the scan test result of a unit in the order.

The testing that is done in a factory to classify a filter and the test that is done after the filter has been installed to determine if there are any leaks are entirely different forms of testing. The factory test is meant to classify the filter's efficiency before it is shipped. The installed leak scan is used to verify the integrity of the filter and its seal in the field.

Both tests serve a purpose but do not ｒｅｐｌａｃｅ each other. The method by which installed leak testing is done and the acceptance criteria are established in accordance with the facility's qualification protocol. The cleanroom standard iso 14644-3 refers to several methods of testing cleanrooms that include installed-systems testing but does not supersede the filter element classification standards [2].

The cleanroom standard iso 14644-1 classifies the air cleanliness of cleanrooms on the basis of particle concentrations but does not assign H13 HEPA filter or H14 HEPA filter class to a filter [1].

The DOP test port specifically designed for cleanroom HEPA filter use makes it possible for verification to take place without filter removal. This inability to remove the filter itself will not result in inevitable failures in all applications, but it is considered common practice in the pharmaceutical and semiconductor industries because production downtime is costly.

Case Study: Optimizing Pharmaceutical Cleanroom Performance

The following case has been submitted as a qualitative summary of the project based on files provided by the project manager. The numerical data associated with particle count, energy use and specifications are not included because the required file has not been provided.

Project Challenges

The project involved a packaging cleanroom for the pharmaceutical industry which had to meet the class 1000/ISO 6 standard. The project site was located in an area where there existed a high ambient particle load due to the activities of adjacent industries and it had low ceiling clearances. As a result, pressure drops that were required for maintaining proper air movement in the cleanroom also had to be maintained at given limits.

It should, however, be noted that class 1000 is an older cleanliness category and should not necessarily be considered as equal to ISO 6 in every situation. On the contrary, the specific measurement conditions and particle size criteria must be established to understand if Class 1000 and ISO must indeed be treated as interchangeable.

The Deiiang Solution and Results

Deiiang provided narrow profile H14 HEPA filter units, which measured 592 mm wide by 592 mm high by 292 mm deep. Each filter was capable of handling airflows of up to 2,500 m³/h through about 20.04 m² area of filtering surface with initial pressure drops being well under 220 Pa.

In addition, the project utilized silicone-free gasket materials which allowed it to maintain better compatibility with decontamination agents used by the client's facility; the pre-filters of F7 duty were used prior to HEPA filters. Prior to shipment, each filter was actually tested for performance according to DOP standards.

According to project documents, actual particle counts went from an ISO 7 level going to the claimed status of ISO 6 level after the cleanroom was set up.

In order to substantiate the positive result claimed in this article, an array of supporting evidence needs to be established including pre- and post-installation particle count records, sampling conditions and locations, particle size channels, certification for the installed filter units, along with the energy consumption/fan power consumption data including previous knowledge regarding the baseline. The project should be regarded as project-reported outcome until such documentation is available.

The article does not specify any energy savings that are attributed to this article either. That being said, one needs to confirm that the classification for the final room was independently verified according to ISO 14644-1 methods based on the information recorded during the project.

Figure 9: Summary chart showing the project process from establishing a baseline to selecting a filter and installation and commissioning. No numeric particle-count readings have been included since the project report did not include any verified measurements.

Selecting the Right HEPA Filter for Your Facility

Choosing the HEPA filter requires matching the specification to the four-part HEPA filter rating the project calls for. The HEPA filter class has to reflect the cleanliness target. Cleanliness standard should reflect applicable compliance framework. Operating limits should reflect the installation conditions. The documentation regarding testing has to correspond with the facility qualifications.

The logical selection process will help accomplish this task in the right order:

1. Determine required room performance, standard cleanliness, and project qualification.
2. Determine design airflow, available face area, and installation depth.
3. Determine initial and final resistance with respect to fan capacity and pressure-drop budget.
4. Choose H13, H14, or ULPA only based on the design and the cleanliness target.
5. Check housing size, frame design, gasket size and type of gasket used for sealing.
6. Define the classification evidence required and, if applicable, the per-unit scan documentation.
7. Confirm the method of installing and the criteria for testing leaks.
8. Define the replacement strategy in connection with the differential pressure limits, integrity test results and guidance from the manufacturer.

Example: Illustrative product data comparison. Assume a project requires a HEPA filtration stage rated for approximately 2,500 m³/h with a depth of 292 mm and a catalogue budget for initial resistance of around 220 Pa.

The Deiiang Combined H14 HEPA filter in 592 × 592 × 292 mm (four-pleat) has these numbers at the catalogue level: 2,500 m³/h, 20.04 m² of filter area, ≤220 Pa initial resistance, final resistance of 400–600 Pa. This is an illustrative product data comparison and is not a blanket recommendation.

The engineer must still verify that the housing will accommodate the dimensions and gasket profile, the fan can deliver 2,500 m³/h under the final loaded resistance and that the project's qualification protocol accepts the model-specific classification report and per-unit scan documentation.

On a separate point, ISO 14644-1 classifies the cleanliness of cleanroom air based on airborne particle concentration. It does not stipulate a specific filter class. The relationship between the cleanliness classification of the cleanroom and the filter class required to meet the cleanliness level is dependent upon system design, airflow pattern, integrity of installation, operational state, and qualification test results. Choosing either an H13 HEPA filter or H14 HEPA filter does not automatically mean that an ISO class is established.

Key Verification Checklist for Buyers

Below is an important checklist for contractors, facility engineers, and procurement teams. Please use the checklist to ensure compliance with your filtration system:

Additional possible pitfalls in commissioning include:

• Compression of the gasket may be uneven if the housing surface is not flat. Make sure to use a straight edge to verify uniform contact of the gasket.
• The DOP test port of the DOP Integrated filter must remain accessible post installation. Check the ceiling grid to ensure access is not blocked.
• The initial resistance measurement when commissioning should be recorded with the airflow value at the moment of measurement so that the baseline is equal to future resistance measurements for comparison purposes.

Conclusion: Partnering with Deiiang

Deiiang is a manufacturer of air filters and cleanroom equipment and provides H13 HEPA filter and H14 HEPA filter products in the Combined and DOP Integrated product lines and U15–U17 rated products in the Super High Efficiency Baffle-Free product line. F5–F9 pre-filters are used to ensure that HEPA equipment is protected. All statistics, specifications, and information listed in this publication are from Deiiang's catalog.

The pharmaceutical cleanroom project referred to in this document is presented herein as a case study. Neither is a site-specific performance guarantee; they are simply examples.

Designed by Jason Peng and his engineering team, Deiiang works with facility managers, HVAC contractors, and cleanroom integrators to develop the right filter for specific projects. Engineers can prepare drawings, rated airflow information, plenum height and width dimensions, required class and standard, permitted pressure drop, gasket design needs, and testing and certification requirements, specific for the project.

Each project should have its own unique solution based on site information and individual compliance requirements established by applicable regulations. Specific product family and types of orders: catalog specifications, model-specific classifiers, and unit testing documents. Not all documents will necessarily be available for each model and the proper options will depend upon the order specifications and jurisdictional requirements.

Frequently Asked Questions

What does a HEPA filter rating mean?

It describes the filter's ability to capture particles at a specified size under a defined test method. Check the applicable standard and test conditions when comparing ratings.

What is the typical efficiency of a HEPA filter?

Common HEPA classifications specify at least 99.97% HEPA filter efficiency at 0.3 micrometers in some markets. Requirements vary by standard and filter class, so confirm the product's documented rating.

Is a HEPA rating the same as a MERV rating?

No. MERV ratings classify filters under a different test framework, while HEPA filters are classified using HEPA-specific standards. The ratings are not directly interchangeable.

How is hepa filter efficiency tested?

A defined aerosol challenge is passed through the filter, and particle penetration is measured under specified test conditions. The method and particle-size range depend on the standard used.

Does a higher HEPA rating always mean better performance?

Not necessarily. Consider the required efficiency alongside airflow, pressure drop, sealing, operating conditions, and the applicable cleanroom or HVAC requirements.

What should buyers check before selecting a HEPA filter?

Verify the filter class and test standard, rated airflow, pressure drop, dimensions, sealing design, materials, and supporting test documentation.

References

• [1] iso 14644-1:2015 — Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness by particle concentration — International Organization for Standardization. Makes classification based on particle concentration and does not assign a class H13 or H14 for a filter.
• [2] iso 14644-3:2019 — Cleanrooms and associated controlled environments — Part 3: Test methods — International Organization for Standardization. Specifies the cleanroom test methods and including relevant installation-system tests and does not ｒｅｐｌａｃｅ the classification tests for the filter element.
• [3] EN 1822-1:2019 — High efficiency air filters (EPA, HEPA and ULPA) — Part 1: Classification, performance testing, marking. European Committee for Standardization.
• [4] EN 1822-4 and EN 1822-5 — Test methods for filter elements and filter media. European Committee for Standardization.
• [5] ISO 29463-1 — High efficiency filters and filter media for removing particles in air — Part 1: Classification, performance, testing and marking. International Organization for Standardization.
• [6] IEST-RP-CC001 — HEPA and ULPA Filters. Institute of Environmental Sciences and Technology. Consumers must confirm they have the right edition and title of the information and also should ensure the exact references made in the material are encompassed by any clause.
• [7] EN 779:2012 — Particulate air filters for general ventilation — Determination of the filtration performance. European Committee for Standardization. Old classification which has been superseded in a number of different market places by ISO 16890.
• [8] ASHRAE Standard 52.2 — Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. ASHRAE.
• [9] US MIL-STD-282 — Method of Test for Filter Units, Protective Clothing, Gas-Mask Components and Related Products. United States Department of Defense. An old specification for the United States.
• [10] Deiiang Combined High Efficiency Filter catalogue, DOP Integrated Filter catalogue, Super High Efficiency Baffle-Free Filter catalogue and F5–F9 Pre-filter catalogue. Deiiang also supplied product data.