One important system to consider in sterile processing departments (SPDs) is the heating, ventilation, and air conditioning (HVAC) system(s) serving these spaces. In addition to providing thermal comfort and relative indoor air quality for occupants, the HVAC system can either support or hinder infection prevention objectives in SPDs.

A wide variety of field conditions exist in SPDs at acute care facilities nationwide. In addition, the “rules” (codes, standards, specifications, and regulations) adopted and applicable can vary from state to state and facility to facility. Compliance with the rules, which take effect at the time of construction or renovation, is intended to support the proper design, installation, and operation of the building and its systems. Once commissioned and occupied, the building and associated systems take on a life of their own, requiring life cycle oversight, maintenance, and support.

This article on HVAC and infection prevention considerations in SPDs focuses on a two-room setup with a designated “dirty side” and designated “clean side.” Rather than being a comprehensive guide for the maintenance of HVAC systems in SPDs, this article is intended to highlight some considerations from an industrial hygiene perspective.

Air Handling Unit

Let's begin with the air handling unit (AHU), or units, serving the SPD. A great deal of attention has been given to monitoring temperature and humidity within SPDs. It is well understood that excessive temperature and/or humidity can lead to microbial growth, which could undermine sterilization practices and lead to downstream health-care-associated infections (HAIs). Solely monitoring the temperature and humidity in the unit or associated ductwork itself may not adequately represent the conditions realized in the rooms or in micro-climates within a given room. Is the air within the rooms properly mixed with sufficient air exchanges? To what extent do fugitive steam, condensate run-off, or hotspots from equipment affect temperature and humidity?

Is the air being supplied by the AHU clean enough? The answer to this question begins at the outside air intake on the AHU. Does intrusion or ponding of water and associated microbial growth occur near the intake? Are exhaust fans within close proximity to the air intake?

The next consideration is the AHU itself. As the coils within the AHU facilitate condensation and moisture removal from the intake airstream, is the condensate effectively drained from the system? Accumulation and retention of water within the system could certainly lead to microbial growth in the unit.

Another consideration is the filters within the AHU. Assuming that properly rated filters are being used in the AHU, are the filters properly seated in their filter racks and effectively gasketed to prohibit filter bypass? You may have highly effective filters in an AHU, but if air is going around rather than through the filters, the quality of supplied air could be affected considerably.


Next in line is the ductwork. Does significant leakage occur at ductwork connections, access panels, or variable air volume devices? Loss of supply air via leakage could undermine the functional air exchanges in the spaces served. In addition, loss of that supply air (especially in months of cooling demand) could lead to hidden surfaces above the ceiling that are cooled sufficiently to become condensing surfaces (i.e., surfaces at or below dew point temperature), leading to moisture accumulation and potential microbial growth. If thermal insulation on supply air ductwork has been subject to moisture accumulation, the insulating capacity or R-value would likely be compromised through compression of the insulating material. Once insulation is compromised, condensation and water accumulation gets progressively worse.

Room Pressurizations

Now we are at a point of considering room pressurizations achieved by the HVAC system. “Clean toward dirty” airflow is a fundamental infection prevention objective. Clean air leakage into adjacent, less clean or dirty areas is beneficial dilution. Leakage of dirty air into clean spaces leads to potential contamination.

In a typical two-room sterilization configuration, the dirty side of the SPD is negatively pressurized to contain the dirty air. This is accomplished by having more air volume removed from the room compared with lower air volume delivered to the room by ductwork. The opposite applies to the clean side. Higher supply air volumes, as compared with collective exhaust/return air volumes, results in positive air pressurization intended to keep dirty air out.

One item to consider on the positively pressurized clean side is the presence of fugitive steam. If significant fugitive steam is present, the positive air balance of the room can effectively force that moisture into adjacent walls and ceilings. Care should be taken to ensure that building finishes selected for walls/ceiling in SPDs do not facilitate absorption of moisture. Any caulking at the junctions of building materials and finishes should be maintained to prohibit the passage and accumulation of moisture.

Flowrates of supply air and exhaust/return air to achieve positive and negative pressurization are based primarily on the cubic foot size of a given room. Sometimes rooms are functionally bigger than we realize. If significant air leakage occurs in perimeter walls, floors, or ceilings, the “size” of the room is affected. Doors and pass-through window openings also can undermine the maintenance of protective airflow.

The pressure on one side of a barrier always is affected by adjacent pressures. The impact of adjacent room and corridor air pressures ranges from negligible to significant. For example, let's consider an SPD within proximity to central receiving and the loading dock. Variations in outside air intrusion via the loading dock could certainly affect interior room-to-room pressure differentials.

Another example would be elevator shafts within or in close proximity to the SPD. As the elevator cab plunges up and down, significant variation in room pressurizations can occur. Any change in functional air balance of neighboring AHU zones also could have significant impact on individual room pressurizations. Fire dampers in ductwork that do not open after fire alarm testing are common culprits.

Heating, ventilation, and air conditioning (HVAC) systems can support or undermine life cycle infection prevention objectives in sterile processing departments (SPDs). Effective monitoring and maintenance of HVAC systems in SPDs and adjacent spaces are vital to minimizing microbial growth and the downstream potential for healthcare-associated infections.

Heating, ventilation, and air conditioning (HVAC) systems can support or undermine life cycle infection prevention objectives in sterile processing departments (SPDs). Effective monitoring and maintenance of HVAC systems in SPDs and adjacent spaces are vital to minimizing microbial growth and the downstream potential for healthcare-associated infections.

Recent nearby renovations (and associated air balancing) also can be problematic. Near the completion of a renovation or construction project that has a significant HVAC component, a process know as test and balancing (T&B) is performed. T&B is a systematic process to adjust airflows in and out of a given space to achieve mechanical design parameters. Functionally, T&B is usually limited to the actual footprint of the renovation project. In achieving targeted design parameters in one space, oftentimes air is taken from adjacent spaces or relieved to adjacent spaces. As more and more renovations proceed through time, the overall air balance of a given AHU zone, floor level, or entire facility can be progressively affected.


HVAC systems in SPDs have the potential to support or undermine life cycle infection prevention objectives. Microbial growth and the downstream potential for HAIs can be minimized through consistent and effective monitoring and maintenance of HVAC systems in SPDs and adjacent spaces.

Author notes

James (JJ) Jenkins, MSPH, is owner of Jenkins Risk Management, LLC, in Fort Mill, SC, and chief executive officer of the Construction Infection Control Training Institute in Fort Mill, SC. Email: