What is the MERV rating for HEPA filters?

HEPA filters do not have a MERV rating. MERV is defined by ASHRAE Standard 52.2 for general ventilation filters, having a scale that goes up to MERV 16. There are different standards by which HEPA filters are classified under, mainly EN 1822 and ISO 29463. The two different standards cannot be converted into eACH other [1][2][3].

This article explains the importance of making the distinction between the two in order to be helpful in making decisions about HVAC and cleanrooms. It looks at the differences in testing, how to practically select based on the standards, how to verify that the standards apply, and more.

The MERV scale and HEPA classification provide different answers to the same question. MERV provides information on how efficiently the filter captures particles based on ranges of particle sizes. Any MERV rating chart stops at MERV 16, which is exactly why it cannot express HEPA performance. On the other hand, the HEPA classification provides information on the efficiency of the filter as it pertains to the most penetrating particle size using a different test method [1][2][3].

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If someone is seeking out the HEPA filter MERV rating, he or she is usually looking to compare the products. The best way to do this is to make a proper comparison of each filter using the appropriate standard rather than requesting a fictitious MERV value.

There is a specific set of efficiency criteria for HEPA classifications, and it is not possible to compare HEPA classifications directly against MERV 16 using only the published class labels. Understanding why those gaps exist is the starting point for working with HEPA filtration standards. This does not mean that different standards cannot be compared, but rather that actual values according to the specific application must be determined.

The direct answer: HEPA filters do not have a MERV rating

It is impossible to assign a MERV rating to HEPA filters because MERV is defined for filters tested according to ASHRAE 52.2's methodologies [1]. HEPA filters are classified in accordance with standards such as EN 1822 or ISO 29463 which test HEPA filters using different aerosols and basis for particle-size distribution as well as criteria for acceptance [2][3].

As a result, there is a simple practical outcome from this. Customers that need HEPA performance must indicate which applicable HEPA standard they want as well as class and test documentation. Indicating to receive something that is "MERV equivalent" gives no surety of specifications. Anyone asking what is the MERV rating for HEPA filters should instead request the class and the test report.

Many companies supply information about high-efficiency filters in terms of "MERV 17-20." These descriptors do not belong in ASHRAE 52.2 and cannot be considered MERV ratings and should only be viewed as a selling strategy unless such statements can be backed up with name of standard and test document.

Why can't a HEPA filter be assigned a standard MERV rating?

The MERV scale was developed under the auspices of ASHRAE 52.2 and relates to the performance of general ventilation filters as measured within three particle-size bands [1]. The highest MERV rating, MERV 16, means that filters must meet specified efficiencies within these bands.

On the other hand, HEPA classification begins with the application of "most penetrating particle size" which is particle size that HEPA filters are designed to most efficiently remove [2]. The most penetrating particle size varies depending on which filter media and test conditions are used. Specifics of how these classifications take place are provided by standards such as EN 1822 and ISO 29463 [3].

The U.S. HEPA definitions referring to 99.97% efficiency at 0.3 micron size of particles are based on other criteria [6]. There are minimum MPPS-based specifications for H13 and H14 Europeans [2]. The parameters vary based on their respective standards.

What does "HEPA equivalent to MERV 16" mean—and why is it misleading?

The terminology implies that there is a continuum with HEPA being above MERV 16. This is not true since MERV 16 is the maximum possible score, according to ASHRAE 52.2 [1]. Furthermore, HEPA has distinct means of classification.

Testing for a MERV 16 filter and a HEPA filter differs due to the fact that MERV has a banded method of reporting minimum efficiencies, whereas HEPA relies on an MPPS approach [2][3].

Therefore, it is incumbent on the buyer to regard the word "equal" as informal since the proper specification is the HEPA classification.

How MERV and HEPA filters are tested

The methodology used in testing results in a lack of interchangeability of data. MERV testing uses particle size bands [1]. EN 1822 and ISO 29463 use the MPPS as the basis for the testing [2][3].

IEST-RP-CC001 provides acceptable practices for HEPA and ULPA filters [5]. MIL-STD-282 provides historical data related to US standards [6]. EN 779 is a device used for prefilter classification [7].

Table 1: Current Classification Systems Comparison

Table 1: Current Classification Systems Comparison.

How does ASHRAE 52.2 determine a MERV rating?

ASHRAE 52.2 tests filters in a specified duct with an established aerosol challenge. Particles are accounted for upstream and downstream across three sizes: 0.3-1.0 µm, 1.0-3.0 µm and 3.0-10.0 µm [1].

Minimum performance within each size range determines MERV ratings, with MERV 16 being over 95% efficient in each tested range. There is an established loading procedure used in reporting the minimum composite efficiency.

How do HEPA standards classify and verify filter performance?

Filters are classified using EN 1822 and ISO 29463 through their effectiveness at the most penetrating particle size [2][3]. The most penetrating particle size is defined as the size of the particle being tested at which the filter works at its least efficiency.

Testing is performed by scanning the face of the filter with the aerosol challenge to determine any holes, defects in the seals, and localized areas of performance defects. That scan is the accepted way to verify HEPA filter particle capture in a finished unit. The specific requirements for scanning are determined based on the standard, part, and class [2][3].

The combined H13/H14 filter efficiency from the Deiiang catalog is in the 0.3 µm size range. H13 is given at 99.97% to 99.99% while H14 is stated at 99.995% to 99.999%. These results only apply to the catalog figures at fixed particle sizes and they need to be verified against the model-specific EN 1822 test report.

Comparing HEPA filters with MERV 16 and other high-MERV filters

This comparison shows the relative classification bases and not the performance ranking for HEPA filters. Buyers often frame it as HEPA vs. MERV 16, but no direct conversion exists. The values are from other standards and must not be treated as equal.

MERV 16 is the highest rating in the ASHRAE 52.2 rating system [1]. In practice, HEPA filters perform better than this level, but they use a different classification system with its own acceptance criteria [2][3].

Table 2: Filter Classifications and their Classification Bases

Table 2: Filter Classifications and their Classification Bases.

How does HEPA filter efficiency compare with MERV 16?

The two numbers are based on different methods and different particle sizes, therefore a true performance comparison cannot be made simply based on the class labels. Similar testing conditions would need to be met.

As arithmetic only, if an air filtration system captures 95% of particles, it will allow through 5%. On the other hand, if the efficiency of a filtration system is 99.95%, it will only let through 0.05% of particles. Readers should refer to the specific test report of the filtration system in question.

When is a high-MERV HVAC filter more appropriate than HEPA filtration?

The correct choice will depend on many factors including design airflow capacity, the amount of pressure available in the system, how much resistance is created by the filter itself, and the level of cleanliness required for the application. There is no hard and fast rule for determining which method is more suited.

In some cases, if HEPA filtration is not necessary, it may be sufficient to use filtration systems with high-MERV ratings. These filters operate with far lower pressure drops than HEPA filtration does. If the system cannot handle the added resistance of a HEPA stage, a high-MERV filter may be the practical choice.

Choosing filtration for HVAC systems and cleanrooms

Selection begins with the application. General HVAC, hospital wards, pharmaceutical cleanrooms, and semiconductor fabs each have different requirements.

iso 14644-1 classifies cleanroom air cleanliness by particle concentration [4]. It does not assign a filter class. The filter class depends on system design, process risk, and qualification requirements.

HVAC HEPA filters are used in systems designed or modified for their resistance. Cleanroom HEPA filters are installed in terminal housings or ceiling grids with sealed interfaces and integrity testing. Choosing an air filter for cleanrooms is therefore a system-level decision, not a catalogue lookup.

What should HVAC contractors check before installing a HEPA filter?

Contractors should find out what the design air flow, the static pressure of the fan available, and the HEPA filter resistance at the desired air flow are.

According to the formula, "The required static pressure is obtained from the existing resistance plus the HEPA filter resistance at the rated air flow." The system is not compatible with the fan without upgrading, when the total exceeds the fan rating.

System housing dimensions, filter depth, sealing interface, and prefiltration area should also be considered. Installing a preliminary stage will ensure that the HEPA filter is protected and increases its working period.

How should cleanroom buyers select a HEPA filter for their classification?

The cleanroom must first be defined as per the class of cleanliness required as per ISO 14644-1. The HEPA filter class should then be determined according to the structure design, risk management, and requirements of the project.

Simply determining the ISO room class does not specify what filter class should be used. Factors affecting this are the room design, air-change rate, airflow pattern, process risk, terminal filtration, and qualifications.

In some cases, an H13 filter may be applicable to all iso 7 and 8 applications, while in others, an H14 filter may be recommended for iso 5 or 6 projects.

Airflow resistance, installation, and system compatibility

HEPA filters present a greater resistance than MERV filters. The correct resistance should have been ensured from the manufacturer.

The system must be checked to determine resistance both at the front and back ends. A filter that works effectively at its first resistance might not work at its ultimate resistance if the fan is unable to achieve the airflow necessary.

The quality of the installation can also play a crucial role in its function. Filter bypass leakage around the filter frame could undermine its efficiency and the filter housing must be sealed against the filter frame.

How does HEPA filter pressure drop affect HVAC performance?

Every fan has a pressure-airflow curve. If resistance increases, the fan moves less air. How much it drops depends on the curve of the fan and resistance of the filter at the operating point.

Let's make a calculation: Let us assume there is a fan with the performance of 5,000 m³/h at a pressure of 400 Pa. After the increase of the resistance of the filter to 600 Pa, what is the airflow of the fan? The actual value will have to be taken from the curve of the fan.

Deiiang catalogue mentions initial resistance value of less than or equal to 200 Pa (H13) and less or equal to 220 Pa (H14) for the Combined family of filters at the given airflow. Final resistance is stated as between 400-600 Pa. These are catalogue values under elaborated conditions.

Which installation details prevent air bypass around a HEPA filter?

To prevent bypass, the gasket design and the condition of the housing should be confirmed. The filter frame and gasket design should match the housing.

• Place the filter directly in front of the frame or grid.
• Tighten clamping to specified compression requirements.
• Check the full perimeter for seal contact.
• Record the installation date and initial resistance.

Gel and knife-edge seals form an effective sealing interface for critical applications. Mechanical gaskets work for flat surfaces [5].

Verification, maintenance, and documentation

Verification ensures that a filter operates according to specifications. The factory classification, per-unit testing and installed leak testing processes are different and answer different questions.

Factory classification determines the product family performance within the standard. Per-unit testing ensures that the specific filter meets the acceptance criteria. Installed leak testing ensures that the filter, seal and housing interface are leak-proof [3][8].

Maintenance is based on conditions. Differential pressure readings are the first indicator of a problem. A sudden drop indicates a possible media failure, seal failure or other issue. It should lead to further investigation, not diagnosis.

What documents should accompany a HEPA filter purchase?

The purchase should include model specific classification report, per-unit test results at the very least and the catalog data sheet [2][5].

The classification report should mention the applicable standard, edition, test method and classification. The per-unit test shows that the specific filter meets the acceptance requirements.

Deiiang confirms that the filters are thoroughly tested before being shipped. Specific information for each model should be checked with Deiiang for model-specific order information.

How should facility teams verify an installed HEPA filter?

Facility personnel should follow the general qualification protocol of the project. iso 14644-3 lays down the test methods to be adopted in the cleanroom, including the installed filter leak test [8]. iso 14644-1 indicates the air cleanliness classes of the room according to its particle concentration [4]. However, it does not provide the verification standard for gas removal.

For the project, acceptance criteria and procedures must be established, depending on the applicable standard. The leak test method and the type of aerosol depend on the standard and the requirements of the facility as well [8].

Deiiang product data and real-project application

Deiiang is a manufacturer of cleanroom and air filter. Its catalog contains information on both particle filters H13 and H14 and ULPA filters U15-U17. All the figures in this section are from Deiiang catalog regarding the mentioned models.

Combined High-Efficiency Filter is meant for terminal filtration in air-conditioning systems and purification equipment with a high air volume flow. The filter makes use of ultrafine glass-fiber media, separator-less design, EVA hot-melt spacers, PU seal, and ABS frame.

Which Deiiang hepa filter specifications should buyers compare?

The buyers should compare airflow, media area, initial resistance, and class of efficiency for every model.

• Combined 287×287×292 mm = 550 m³/h; 4.63 m²
• Combined 592×592×292 mm = 1,900 m³/h; 15.03 m²
• Combined 592×592×292 mm (4-pleats) = 2,500 m³/h; 20.04 m²
• Combined 592×490×292 mm = 2,050 m³/h; 16.44 m²
• Combined 592×287×292 mm = 1,150 m³/h; 9.26 m²

The initial resistance value is ≤200 Pa (H13) or ≤220 Pa (H14) while the final pressure is in range 400-600 Pa. The values mentioned here are catalog values at rated airflow. Performance is confirmed from the corresponding EN 1822 test report.

What can a real cleanroom project reveal about HEPA filter selection?

The following example illustrates the general process of one cleanroom project and is therefore anonymized. Project results are reported as project-reported outcomes.

The cleanroom project involved the installation of H14 HEPA filters. The cleanroom was to maintain iso 6 cleanliness levels, requiring that Deiiang provide 592 mm × 592 mm × 292 mm filters with 2,500 m³/h of volumetric air discharge, a minimum media area of 20.04 m², and an initial resistance of not more than 220 Pa.

Silicone-free gaskets and F7 pre-filters were added along with DOP scan testing per unit. Project results were reported with ISO 6 operations after installation. Prior test results regarding energy consumption and measured particle counts must be verified through original documentation sources.

How to specify and buy HEPA filters confidently

A procurement checklist helps buyers confirm that the filter matches the application and the compliance framework.

Table 3: Checklist for HEPA Filter Procurement

Table 3: Checklist for HEPA Filter Procurement.

Do not accept MERV Rating in place of HEPA Class. A MERV 16 filter is not equal to HEPA class H13 or HEPA class H14. Compare filter performance under the same standard and testing basis.

What information should a HEPA filter RFQ include?

The complete RFQ needs to specify design flowrate, required cleanliness level, applicable standard, and target class.

• Flowrate in cubic meters per hour.
• Filter face dimension and available depth.
• Target standard and class.
• Initial and final resistance limits.
• Operating temperature in Celsius and relative humidity.
• Gasket and sealing requirements.
• Documentation required according to the tests.
• Specific requirements of the unit documentation.

An easily downloadable checklist of RFQs can serve as a helping tool for the buyer to collect the necessary information before asking the supplier for quotations.

How can buyers compare supplier claims without relying on MERV labels?

The buyer will need to ask for the model-specific classification report under EN 1822 or ISO 29463 [2][3]. The report needs to include the specific standard, edition, test method, and category.

If a supplier states "HEPA equal to MERV 16," request the relevant test data. A classification report should back this claim, not the MERV label.

For cleanroom use, the filter should be tested according to the relevant standard with documentation. MERV ratings cannot serve as a substitute for HEPA classification.

Frequently Asked Questions

What is the MERV rating for a HEPA filter?

HEPA filters do not have MERV ratings. MERV is for filters that were tested with ASHRAE 52.2, using a scale from 1 to 16. HEPA filters use different standards (EN 1822 or ISO 29463) and different testing methods.

Is a HEPA filter equivalent to MERV 16?

No, they are not the same. MERV 16 is the highest rating on the ASHRAE 52.2 scale. HEPA filters perform better than MERV 16 but fall under a different testing standard and thus have different acceptance criteria.

How efficient is a HEPA filter?

The U.S. HEPA convention is 99.97% at 0.3 microns. With EN 1822, H13 must be at least 99.95% at the most penetrating particle size (MPPS) and H14 must be at least 99.995%. According to Deiiang catalogue data, H13 efficiency is 99.97–99.99% and H14 is 99.995–99.999% at 0.3 microns. These figures should be verified with the model-specific EN 1822 report.

Can I use a HEPA filter in a standard HVAC system?

The installation of a HEPA filter in most HVAC systems would require some modifications. Due to the fact that HEPA filters present high pressure drops, regular HVAC fans will not have the capability of handling such additional load. The process would need the fan to be replaced, changes to the housing, and improvements on the sealing. Compatibility of the HVAC system should be verified against the fan curve before purchase.

Are HEPA filters suitable for cleanrooms?

It is possible to implement HEPA filters into a cleanroom HVAC system. Filter class will depend upon cleanliness target, system layout, process risk, and project requirements. ISO 14644-1 discusses classification of the room, not of the filter [4]. Common options include H13 and H14, which is specific to the project.

How should I compare HEPA and MERV filters?

Compare filters according to their own criteria. Use MERV for general ventilation applications and EN 1822 or ISO 29463 for HEPA classification [1][2][3]. Do not attempt to convert MERV to HEPA. If a project calls for HEPA performance, indicate the appropriate standard and class.

References

• [1] ASHRAE Standard 52.2 — Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. ASHRAE.
• [2] EN 1822-1:2019 — High efficiency air filters (EPA, HEPA and ULPA) — Part 1: Classification, performance testing, marking. European Committee for Standardization.
• [3] ISO 29463-1:2024 — High efficiency filters and filter media for removing particles in air — Part 1: Classification, performance, testing and marking. International Organization for Standardization.
• [4] iso 14644-1:2015 — Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness by particle concentration. International Organization for Standardization.
• [5] IEST-RP-CC001.7 — HEPA and ULPA Filters. Institute of Environmental Sciences and Technology. Verify current edition and title.
• [6] US MIL-STD-282 — Method of Test for Filter Units, Protective Clothing, Gas-Mask Components and Related Products. United States Department of Defense. Historical specification.
• [7] EN 779:2012 — Particulate air filters for general ventilation — Determination of the filtration performance. European Committee for Standardization. Legacy classification.
• [8] iso 14644-3:2019 — Cleanrooms and associated controlled environments — Part 3: Test methods. International Organization for Standardization.
• [9] Deiiang Combined High Efficiency Filter catalogue, DOP Integrated Filter catalogue, Super High Efficiency Baffle-Free Filter catalogue, and F5–F9 Pre-filter catalogue. Product data supplied by Deiiang.