Selecting a cleanroom for a new business or new product is not as difficult as it may seem. While there are many options and features to consider, focusing on your key requirements will help make the decision making process easier.

Cleanroom Selection Criteria

Applicable Rules & Regulations

Rules mandated by government regulations, ISO guidelines, or customer requirements are the first key consideration when selecting a cleanroom. For example, government regulation USP797 outlines specific requirements for the manufacture of pharmaceutical products; ISO 14644-5:2004 guidelines specify basic requirements for cleanroom operations. Most often, regulations or customer specifications will dictate the cleanliness level or rating required, which provides a good starting point for choosing the right cleanroom.

Cleanroom Cost

Cost is also an important consideration, especially if you’re starting a new business or developing a new product line. Prices can vary greatly, from custom, fixed-wall construction to modular, free-standing, softwall or hardwall cleanrooms. Fixed wall rooms are typically the most expensive, with modular softwall cleanrooms being the most economical. Additionally, size, shape, configuration, and accessories will all affect the overall cost.

Other Considerations

The location of your cleanroom within your existing building structure, and the number of processes and workers needed in cleanroom, will determine the size and shape of the room. Cleanroom aesthetics are also important: projecting a high-tech image with visual appeal can help attract new customers.

Advantages of Modular Cleanrooms

  • Modular cleanrooms reduce design, engineering, and construction time, and thereby reduce costs. Since they are not an integral part of the larger structure, modular cleanrooms can be disassembled and moved to other locations or facilities, or even sold as an asset. Fixed-wall cleanroom construction does not offer this flexibility.
  • Most modular cleanrooms can easily be expanded by removing one or more walls and adding another module. The pre-fabricated design allows the room to be expanded, relocated, or configured into a different shape, or configured into multiple smaller rooms.
  • All air handling and filtration equipment modules are generally built in to the ceiling of a modular cleanroom. Hookups for electrical and plumbing systems are engineered in as part of the design.
  • It takes less time to install a modular cleanroom than it does to construct a permanent fixed-wall structure. Due to the amount of design, engineering, and the various trades involved, it can take several months to construct a fixed-wall cleanroom. However, a sophisticated modular cleanroom can be constructed in just a few weeks. Onsite assembly of a modular cleanroom is also far less disruptive to surrounding operations than permanent construction.
  • Modular cleanrooms also offer potential tax advantages to businesses. They are not typically considered part of the building, and can often be depreciated faster than a built-in, fixed-wall cleanroom. Tax consultants can provide specific tax advantage information.

Cleanroom Construction Considerations

There are two basic types of modular, hardwall cleanrooms: recirculating and non-recirculating. Your product and process requirements will determine which type of cleanroom is best-suited for your needs.

Recirculating Cleanrooms

Recirculating modular cleanrooms recirculate the air within the cleanroom and prevent it from mixing with outside air, providing better control of temperature and humidity. Air is recirculated back to the high-efficiency particulate absorbing, or HEPA, filters located in the cleanroom’s ceiling. This is accomplished via air return chambers built in to the room’s walls or through existing walls of the building.

Recirculating cleanrooms will experience less contamination load on the HEPA filters because the system is recycling previously-cleaned air. With less contamination loading, the filters will last longer and perform better.

Non-Recirculating Cleanrooms

Non-recirculating, or single-pass, cleanrooms draw in air from above the room through the HEPA filters in the ceiling. The filtered air is then blown into the cleanroom and exits through an approximately two-inch gap located below the walls or through adjustable wall grills. Due to the lack of return air ductwork, non-recirculating cleanrooms are less costly to construct than recirculating cleanrooms.

Cleanroom Performance

Testing a Cleanroom: As-Built, At-Rest, Operational

Most businesses are aware of their cleanroom performance requirements because of customer, industry, or government specifications. These performance requirements identify the cleanroom class level required at a given state or condition. There are three levels of condition (states) for testing and characterizing the performance of cleanrooms: as-built, at-rest, and operational. Specific test methods for these three classifications are outlined in ISO 14644-3:2005.

Most cleanrooms are rated and sold in the as-built category: an empty room with the filter system running, but without workers or production equipment. However, adding workers and equipment will introduce contamination and affect the room rating. A cleanroom may be rated ISO 6 at rest, but ISO 7 during operation (see Table 1).

Cleanroom classification chart

To comply with performance requirements, the as-built empty room should be tested and benchmarked, followed by testing and documentation of the at-rest and operational states. If contamination in the at-rest or operational states are not in compliance, corrective steps need to be taken. These steps can range from examining the production process and number of workers in the cleanroom to testing the room’s air flow performance.

Cleanroom Air Flow & Air Changes Per Hour

To ensure optimal cleanroom performance, air flow design and frequency of air changes should be evaluated. Cleanrooms are classified according to the number and size of particles permitted per volume of air in a specific amount of time. There is a relationship between cleanroom class ratings and the room’s air changes per hour. For a cleaner room rating, more air exchanges become necessary. For example, a typical ISO Class 7 cleanroom will have 60 to 150 changes of air per hour, while an ISO Class 6 room will have 150 to 240 changes per hour (see Table 2).

cleanroom classification requirements

All areas within a cleanroom should have similar air changes during each hour to ensure required performance. For example, a cleanroom with only one air return or exit, located at the opposite end of the room from the fan and filter, will likely produce stagnant air spots. This type of design causes air to flow almost horizontally across the room to the venting location, in a line-of-sight fashion. Areas of inadequate air movement retain higher levels of contamination. Adding or moving air returns will enable a more vertical and even air flow, improving overall air quality. The right balance of filter and air returns must be maintained to create positive air pressure inside the cleanroom. Positive air pressure produces outward air movement, preventing the inflow of contaminants and assisting in the expulsion of particles generated by workers and equipment.

Fan Filter Modules

Cleanroom air flow performance can be cost-effectively upgraded by adding fan-filter modules (FFMs). For example, FFMs cover approximately 5 to 15% of an ISO Class 8 cleanroom ceiling; an ISO Class 7 cleanroom requires 15 to 25% ceiling coverage; covering 25 to 40% of the ceiling will upgrade the room to an ISO Class 6.

Cleanroom Options

A variety of accessories are needed to make a cleanroom fully functional: lighting, doors, furniture, changing rooms, etc. Accessories can be selected during the room design and specification phase.

Gowning Rooms & Air Showers

Most cleanrooms have adjacent gowning areas where workers change into special garments to minimize particulate contamination before entering the production area of the cleanroom. Some gowning rooms are equipped with air showers as a method of further reducing particulate contamination that might settle on the surface of a cleanroom garment. Some gowning rooms may have special “clean benches” for people to use while changing into special boots, gloves, gowns, and masks.


Many companies use the gowning room for transferring production material in and out of the clean environment. However, a pass-through, or double-door airlock, is more efficient and keeps the introduction of particulate contamination to a minimum.

Cleanroom Furniture

Specially produced cleanroom furniture and tools should be used, as they are designed for low particulate generation. Choose tables that are smooth and sealed, so they don’t shed particulates and can be easily wiped down.

Cleanroom Site Considerations

The location of your modular cleanroom within your facility is very important. Physical space, temperature, humidity, and cleanliness will affect location selection and overall project cost.

  • Non-recirculating modular cleanrooms can be installed with as little as 25” of clearance above the interior height; recirculating modular cleanrooms require roughly 30” of overhead clearance.
  • A typical cleanroom should operate at 66° to 70°F (19° to 21°C) to ensure a comfortable environment for workers wearing cleanroom garb such as lab coats, head coverings, gloves, and masks.
  • Non-recirculating cleanrooms work best when the space surrounding them is air-conditioned. If supplemental air conditioning is necessary, it can be brought into the space above the cleanroom or directly into the HEPA filters to ensure that the room’s temperature is cooler than the surrounding space.
  • Recirculating cleanrooms provide better temperature control between the interior and the surrounding building space. The room air does not mix with external air, and only requires cooling to compensate for the internal heat load.
  • Processes requiring humidity control require special environmental control systems that are usually only available with recirculating cleanrooms. Typically, systems are made to only add or only remove humidity (not add and remove), depending on the surrounding environment.

On-Site Installation

Installing a modular hardwall cleanroom is quick and easy. There is no need to bring in specialists to assemble the structure. Local tradesmen and internal staff will usually be able to complete installation in a week or less.

Maintenance Considerations

Regular cleanroom maintenance is straightforward, and ensures proper cleanroom performance and classification.

  • Interior surfaces should be wiped down daily on a regular basis or before each shift, using a solution of deionized water at 10% alcohol. Cleanroom floors should be routinely mopped, as well. Vertical surfaces (walls and doors) can be cleaned less frequently, depending on product requirements. All contact points, such as door handles and user-operated equipment, should also be wiped down on a daily or shift basis, again depending on process requirements.
  • HEPA pre-filters must be changed regularly, depending on loading. The HEPA filter modules themselves are maintenance-free, but must be recertified every year. Additionally, proper air flow and leak checks are usually a part of regular certification for a cleanroom.
  • Certification of a room can be performed by either internal personnel or external companies. Most companies prefer an outside, third-party firm to perform the certification and provide them with an independent analysis. Customer or product requirements may require independent certification.


Determining the right cleanroom for a new product or business requires the right balance of many factors, from process requirements and cost to performance and construction. The decision process is not complex, but a clear understanding of cleanroom requirements, regulation, operation, and available options will make cleanroom specification and design much easier.

Contact Clean Air Products today to start designing your modular cleanroom.

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