Custom H13 HEPA Filter for a Pharmaceutical Cleanroom Retrofit

Illustrative Technical Case Study | Pharmaceutical Packaging | Cleanroom HVAC

A pharmaceutical packaging facility operating an aging air handling system faces a difficult replacement decision: how to maintain H13 filtration requirements when standard HEPA filters no longer match the existing installation.

Replacing the entire filter housing would increase the scope of the retrofit, while installing a filter with the wrong frame depth or gasket position could compromise sealing performance.

This technical case study explores a custom mini-pleat H13 HEPA filter configuration designed around three critical constraints: limited installation depth, high-efficiency filtration, and controlled airflow resistance.

This is an illustrative engineering scenario rather than a documented customer order. Dimensions and performance targets are examples for technical discussion.

 

Project Overview

Project Detail	Specification
Industry	Pharmaceutical Packaging
Region	Central Europe (Illustrative Scenario)
Application	Legacy AHU Retrofit
Filter Type	Custom Mini-Pleat HEPA Filter
Nominal Dimensions	592 × 592 × 150 mm
Efficiency Requirement	H13 — EN 1822
Integral Efficiency Target	≥99.95% at MPPS
Design Airflow	1,000 m³/h per filter
Initial Pressure Drop Target	≤160 Pa at design airflow
Frame Material	Aluminum
Proposed Sealing	Continuous Compression Gasket
Project Objective	Fit existing housing without major structural modification

 

1. Project Background: A Replacement Challenge in an Existing Cleanroom

In pharmaceutical packaging facilities, HVAC filtration systems play an important role in maintaining controlled production environments.

However, older air handling units may use filter housings that differ from current standard replacement products.

Consider a pharmaceutical packaging facility in Central Europe preparing to replace the HEPA filters in an aging cleanroom air handling system.

The air handling unit remains operational, but the filter mounting arrangement presents a challenge.

The existing housing has a restricted installation depth of 150 mm and a gasket-sealed frame interface. Standard replacement filters may have different frame depths, flange profiles, or sealing arrangements.

Simply ordering another filter with similar nominal dimensions does not guarantee installation compatibility.

The maintenance team wants to avoid unnecessary AHU modifications while maintaining the required filtration performance.

The central engineering question:

How can a replacement H13 HEPA filter be configured to match the existing housing without compromising the airflow, pressure-drop, and sealing requirements of the system?

 

2. Technical Challenge: Three Requirements That Must Work Together

The proposed replacement needs to address three interconnected constraints.

Challenge 1 — Non-Standard Frame and Installation Depth

The available filter envelope is 592 × 592 × 150 mm.

The external dimensions alone are not sufficient to determine compatibility.

The mounting frame, gasket contact surface, compression allowance, and installation clearances must also be considered.

A frame that fits dimensionally but does not achieve the intended gasket compression may allow unfiltered air to bypass the filter element.

Design requirement: Develop a frame and gasket configuration compatible with the existing filter housing, based on verified mounting dimensions.

Challenge 2 — H13 Efficiency at the Required Airflow

The application specifies H13 filtration according to EN 1822.

For an H13 filter, the integral efficiency requirement is at least 99.95% at the most penetrating particle size (MPPS), together with the applicable local efficiency requirements.

The illustrative operating airflow is 1,000 m³/h per filter.

The challenge is to provide adequate filtration media area within the restricted frame depth while targeting an initial pressure drop of no more than 160 Pa.

Increasing the amount of filter media does not automatically guarantee lower resistance. Pleat spacing, media properties, airflow distribution, and available geometry must be evaluated together.

Design requirement: Select a media and pleat configuration capable of meeting the filtration and pressure-drop targets, subject to testing.

Challenge 3 — Sealing Integrity in a Cleanroom Application

For a gasket-sealed filter housing, the interface between the frame and mounting surface is critical.

An unsuitable gasket position or insufficient compression can create leakage paths around the filter.

In addition, the media-to-frame seal must remain intact under the intended operating conditions.

Design requirement: Specify compatible gasket materials and sealing geometry, with clearly defined inspection and installation verification requirements.

 

3. The Proposed Clean-Link Engineering Solution

For this scenario, a custom aluminum-frame mini-pleat HEPA filter provides a design approach worth evaluating.

Rather than changing the entire AHU housing to accommodate a catalog filter, the replacement filter specification is developed around the existing installation.

A. Custom Aluminum Frame

The proposed filter uses a rigid aluminum frame with nominal dimensions of 592 × 592 × 150 mm.

The design review would consider:

• External length, width, and depth

• Frame profile and corner construction

• Mounting clearance

• Gasket position and compression surface

• Structural suitability for the intended operating conditions

Final tolerances would be confirmed through the approved technical drawing.

The objective is to achieve an installation-compatible filter design without major changes to the existing AHU housing.

B. Mini-Pleat Glass Microfiber Media

A mini-pleat glass microfiber media configuration is proposed to provide the required high-efficiency filtration within the available frame depth.

The design process would evaluate:

• Media efficiency characteristics

• Effective filtration area

• Pleat height and spacing

• Airflow distribution

• Pressure-drop performance at the design airflow

The target is to meet H13 filtration requirements while keeping initial pressure drop within the specified 160 Pa limit at 1,000 m³/h.

The final configuration would be selected only after the relevant design review and performance verification.

Explore Clean-Link's HEPA filters for available configurations and product specifications used in cleanroom and industrial filtration applications.

C. Continuous Compression Gasket

For the illustrated gasket-sealed housing, a continuous gasket is proposed around the designated sealing surface of the aluminum frame.

Gasket material, thickness, width, and placement would be selected according to the housing geometry and required compression.

This approach is intended to support a reliable filter-to-housing interface.

However, the final sealing performance must be verified under the applicable installation and commissioning requirements.

D. Media-to-Frame Sealing

The connection between the HEPA media pack and aluminum frame is another critical component.

A suitable sealant and assembly method would be specified to maintain the integrity of this connection.

The completed assembly would require relevant structural, visual, and filter-element integrity checks.

For projects requiring non-standard dimensions, frame configurations, or specialized sealing arrangements, explore Clean-Link's custom air filter manufacturing capabilities.

 

4. Manufacturing and Quality Verification

For this type of custom HEPA filter, the manufacturing plan would focus on the specifications that matter most to the retrofit.

Rather than treating the product as a standard replacement filter, the frame, media pack, gasket, and testing requirements would be established before production.

Manufacturing Priorities

Frame Accuracy

Confirm the finished dimensions and relevant mounting features against the approved drawing.

Media Assembly

Maintain the required mini-pleat configuration and protect the filter media during assembly.

Sealing Quality

Inspect the media-to-frame seal and gasket arrangement for visible defects and construction consistency.

Handling and Packaging

Protect the filter media, frame, and gasket surfaces during storage and transportation.

Performance Verification Plan

Inspection or Test	Acceptance Requirement
Dimensional Inspection	Conformance to approved drawing
Frame & Gasket Inspection	Conformance to specified construction
Integral Efficiency	H13 requirement: ≥99.95% at MPPS
Local Efficiency	Applicable H13 requirement
Initial Pressure Drop	Target ≤160 Pa at 1,000 m³/h
Filter-Element Integrity	Applicable HEPA leakage requirements
Documentation	Agreed inspection and test records

The final testing program would be confirmed according to the applicable standards, filter construction, and project requirements.

Factory Testing vs. On-Site Verification

Factory testing evaluates the manufactured filter element under defined test conditions.

After installation, the complete filter system may require additional leakage testing to evaluate the filter-to-housing interface and other potential bypass paths.

For cleanroom applications, appropriate installed-filter-system verification should be included in the commissioning plan where required.

A filter that meets its factory efficiency classification does not automatically guarantee a leak-free installed system.

Learn more about Clean-Link's air filter manufacturing facilities, production processes, and quality-control capabilities.

 

5. Expected Project Value and Acceptance Criteria

The primary objective of this retrofit approach is to provide a technically suitable replacement filter without unnecessary modification of the existing AHU housing.

Several practical benefits may be achievable if the proposed design successfully meets its verification requirements.

Reduced Need for Housing Modification

A filter developed around the existing mounting dimensions may avoid the need to replace or significantly modify the filter housing.

This could reduce retrofit complexity and associated installation work.

Specification-Based Replacement

The replacement design would establish documented requirements for filter dimensions, frame construction, gasket arrangement, efficiency, and pressure drop.

These specifications could also support future replacement orders.

Clear Performance Acceptance Criteria

Defined efficiency and pressure-drop targets provide a basis for product evaluation before installation.

Required factory documentation and on-site verification can be incorporated into the procurement and commissioning process.

Better Procurement Planning

For facilities using non-standard or legacy filter housings, a documented custom filter specification may provide an alternative sourcing option when suitable catalog products are unavailable.

What Would Define Project Success?

For this illustrative scenario, success would require confirmation that:

1. The finished filter meets the approved dimensions and construction specifications.

2. The filter achieves the required H13 classification under applicable testing.

3. Initial pressure drop meets the agreed limit at the specified airflow.

4. The filter can be installed with the intended gasket compression and mounting arrangement.

5. Required installed-system verification is completed successfully.

These are proposed acceptance criteria, not results from a completed installation.

 

6. What This Case Demonstrates

A custom HEPA filter retrofit requires more than matching nominal dimensions. Frame compatibility, gasket compression, filtration efficiency, and airflow resistance must be evaluated together.

For cleanroom operators and HVAC contractors, the key is to establish an approved replacement specification covering the filter assembly, performance targets, and installation verification. This can help determine whether a custom replacement is a practical alternative to modifying the existing AHU housing.

 

7. Custom HEPA Filter Manufacturing with Clean-Link

Clean-Link manufactures air filtration products for commercial HVAC, industrial ventilation, cleanrooms, and specialized equipment applications.

For projects requiring non-standard HEPA filter dimensions or installation-specific configurations, our team can review drawings, existing filter specifications, and application requirements to discuss suitable manufacturing options.

Depending on the product design and technical requirements, available customization options may include:

• Custom HEPA filter dimensions

• Aluminum and other suitable frame materials

• Mini-pleat media configurations

• H13 and H14 efficiency requirements

• Gasket and sealing arrangements

• Project-specific inspection requirements

• OEM labeling and packaging

• Bulk manufacturing and repeat supply

Explore Related Capabilities

HEPA Filters

Explore available HEPA filter products and specifications for cleanrooms, HVAC systems, and controlled industrial environments.

Custom Air Filter Manufacturing

Learn more about non-standard filter dimensions, frame designs, gasket arrangements, and project-specific manufacturing options.

 

 

Have a Similar HEPA Filter Retrofit Challenge?

Looking for a custom HEPA filter that fits your existing equipment?

Whether you are replacing a discontinued filter, upgrading an older AHU, or sourcing non-standard HEPA filters for an industrial project, Clean-Link can review your technical requirements.

To request a quotation, please provide:

• Filter dimensions and housing details

• Required HEPA efficiency classification

• Operating airflow and pressure-drop limits

• Frame and gasket specifications

• Application and installation environment

• Estimated order quantity

• Existing filter photographs or technical drawings

Request a Custom HEPA Filter Quote→

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