Healthcare HVAC · HCAI · Published 2026-06-03

Negative pressure rooms and HEPA filtration: California HCAI HVAC requirements for healthcare TI projects

Negative pressure rooms in California licensed healthcare facilities are among the most technically demanding HVAC scopes - and the most heavily regulated. HCAI enforces ASHRAE 170 minimum ACH and pressure relationships, requires OPA-listed HEPA filtration, mandates pressure differential monitoring, and requires ICRA phasing during construction in occupied facilities. This guide covers every layer: the ASHRAE 170 ACH table by room type, OPA equipment requirements, the HCAI plan check sequence, smoke test verification, and the most common correction triggers on negative pressure room submittals.

The regulatory framework: HCAI and ASHRAE 170

California Health Care Access and Information (HCAI), formerly OSHPD, is the state agency that regulates the design, construction, and renovation of licensed healthcare facilities - hospitals, skilled nursing facilities (SNFs), surgery centers, and other licensed healthcare occupancies. HCAI enforces ASHRAE Standard 170 (Ventilation of Health Care Facilities, 2021 edition) as the minimum HVAC design standard for all regulated spaces.

ASHRAE 170 is not advisory - it is mandatory in California for HCAI-regulated facilities. The standard sets minimum air change rates, outside-air requirements, pressure relationships, filtration efficiency, and exhaust discharge requirements by room type. For negative pressure rooms (airborne infection isolation rooms, AII rooms, or AIIR), the requirements are among the most stringent in the standard.

The HCAI plan check process for healthcare TI projects is separate from the local building department process. HCAI reviews the project concurrently with the local AHJ, but HCAI approval is required before the facility can put the space into clinical service. HCAI plan check for mechanical scope typically runs 8–14 weeks. For a full HCAI mechanical submittal checklist, see our companion article on OSHPD/HCAI mechanical submittal requirements.

ASHRAE 170 ACH minimums by room type: the table

ASHRAE 170 Table 7.1 (2021 edition) sets minimum total air changes per hour (ACH) and outdoor air ACH for each room type in licensed healthcare facilities. Key room types relevant to negative pressure design:

Note: ACH requirements are minimums. Higher ACH is always permissible. For rooms with combined functions (e.g., AIIR with anteroom), each space is analyzed separately. ASHRAE 170 Table 7.1 includes many additional room types not listed here. Always consult the current ASHRAE 170 edition adopted by HCAI for the specific project - California may have adopted amendments or updated editions.

OPA-listed HEPA units: the California-specific requirement

For HEPA filtration in HCAI-regulated spaces, California requires that equipment carry an OPA (Office of Product Approval) listing from HCAI. The OPA listing confirms that the specific product model has been reviewed and approved for use in California licensed healthcare facilities. The OPA program covers: HEPA filtration units, portable air cleaning units, negative pressure enclosures, and other specialized healthcare HVAC components.

The practical implication: a HEPA filter unit that meets ASHRAE 170 filtration efficiency requirements (minimum 99.97% efficiency at 0.3 micron per IEST RP-CC001) but is not OPA-listed cannot be installed in a California HCAI-regulated negative pressure room without a specific HCAI equipment approval. The HCAI equipment approval process is separate from the plan check process and requires manufacturer documentation. Specifying OPA-listed equipment from the start - searching the HCAI OPA database before selecting equipment - avoids this problem entirely.

Major manufacturers with HEPA products on the HCAI OPA list include Airomedic, Novatek, and American Air Filter, among others. The OPA database is searchable at the HCAI website and should be the starting point for equipment selection on any California healthcare HVAC project.

Pressure differential monitoring requirements

ASHRAE 170 and HCAI require continuous pressure differential monitoring for AII rooms and other negative pressure spaces. The minimum requirements:

• Pressure differential monitor: A permanently installed pressure differential gauge or electronic monitor, reading the differential between the AII room and the adjacent corridor or anteroom. The minimum required differential is -0.01 inches w.g. (2.5 Pa).
• Monitor location: Readable from outside the room - typically mounted at the door frame or on the corridor side of the room. Some HCAI reviewers require that the monitor be readable from the nurses' station or a remote display, not just at the door.
• Alarm: Audible or visual alarm when pressure drops below the minimum differential. Many facilities integrate the pressure alarm into the nurse call system so staff are notified of pressure loss in real time.
• Calibration: The monitor must be calibrated at commissioning and at regular maintenance intervals. Calibration records are reviewed by HCAI inspectors and accreditation surveyors (The Joint Commission, DNV).

Smoke test verification

HCAI and ASHRAE 170 require that negative pressure be verified by a smoke pencil (smoke trail) test at commissioning. The test procedure:

1. The AII room must be at its design negative pressure differential (doors closed, HVAC operating normally).
2. A smoke pencil is held at the gap below or around the door.
3. When the door is briefly opened, smoke should be drawn into the room - demonstrating that air flows from corridor to room, not room to corridor.
4. The test is witnessed by the HCAI IOR and documented with photographs or video. The IOR records the test in the inspection log.

A common cause of smoke test failure: the AII room was designed for negative pressure, but construction left gaps in the ceiling, walls, or floor penetrations that allow air leakage to equalize pressure. The room appears to be at design differential on the pressure monitor because the monitor is reading a static condition, but the actual airflow pattern is not as designed. Finding and sealing these leaks before the smoke test - not during it - is a key part of HCAI-project mechanical quality control.

ICRA phasing for occupied facility HVAC work

Most negative pressure room additions in California are TI projects within occupied healthcare facilities - the hospital or clinic continues to operate during construction. This requires Infection Control Risk Assessment (ICRA) phasing, which governs how the construction process is managed to prevent fungal, bacterial, and particulate contamination of patient care areas.

For HVAC work specifically, ICRA requirements include:

• Negative pressure construction zone (the construction area is maintained at negative pressure relative to the occupied facility) using portable HEPA exhausters
• Sealing of existing HVAC supply diffusers and return grilles in the construction zone before any demolition - to prevent dust from entering the duct system
• Duct cleaning and sealing verification after duct modifications, before HVAC is restored to service
• Rigid dust containment barriers (not just plastic sheeting - ICRA Class III and IV require framed, sealed barriers with pressure differential verification)
• Daily cleaning of the construction zone and footwear control for workers entering clinical areas

The ICRA phasing plan must be submitted with the HCAI application and approved before construction begins. For a GC managing a healthcare TI, the mechanical contractor's ICRA responsibility is primarily the duct sealing, HEPA exhauster placement, and HVAC system isolation during demolition. Coordination with the GC-level ICRA plan is required. For seismic bracing requirements on HCAI-regulated mechanical systems, see our article on HCAI seismic bracing for mechanical systems. For the full mechanical submittal checklist, see our OSHPD HCAI submittal guide.

Common HCAI correction triggers on negative pressure room submittals

Based on our experience with HCAI submittals, the correction categories that appear most frequently on negative pressure room HVAC submittals:

1. HEPA unit not OPA-listed. The specified HEPA unit does not appear in the HCAI OPA database. Resolution: substitute an OPA-listed model and resubmit.
2. Exhaust discharge location non-compliant. ASHRAE 170 requires that exhaust from AII rooms be discharged at a location that prevents re-entrainment into the building's air intakes. Corrections ask for exhaust discharge location documentation with wind-rose analysis or point-distance from any OA intake.
3. Pressure differential monitor not specified. The design shows a "pressure monitoring device" without specifying the model, range, or alarm setpoint. Resolution: specify the monitor model and confirm it is on the HCAI OPA list.
4. ASHRAE 170 compliance schedule missing or incomplete. The compliance schedule does not list all affected room types, or lists ACH that does not match Table 7.1. Resolution: prepare a complete compliance schedule with ASHRAE 170 table references for each room type.
5. ICRA plan incomplete. The ICRA plan does not address HVAC-specific requirements (duct sealing, HEPA exhauster placement, pressure differential in construction zone). Resolution: supplement the ICRA plan with a mechanical section addressing each HVAC-specific ICRA element.

For GCs pursuing healthcare TI work, our GC Partners page covers Sierra's HCAI experience and IOR coordination process. For project inquiries, contact our bid desk.

Working with Sierra Mechanical on HCAI healthcare projects

Sierra Mechanical Corporation has completed HCAI-regulated mechanical scope in Northern California including AII room additions, operating room HVAC replacements, and pharmacy clean room systems. Our project managers understand HCAI plan check process, OPA equipment selection, IOR coordination, and ICRA phasing requirements for mechanical scope. We maintain a standing library of OPA-listed healthcare HVAC equipment specifications ready for HCAI submittals.

For healthcare TI mechanical scope: contact our bid desk with the facility name, project type, and scope description. Bid desk: (916) 638-8605.

References: ASHRAE Standard 170 (2021 edition) Table 7.1; California HCAI OPA Program; ICRA (Infection Control Risk Assessment) guidelines from APIC and The Joint Commission; California Building Code (2025) Chapter 7A (healthcare). Information current as of 2026-06-03.

This article is general guidance. HCAI requirements vary by project type and facility license. Consult HCAI directly and engage a licensed mechanical engineer and HCAI-experienced IOR for project-specific requirements.