HCAI details 2025 OSHPD amendments to California Mechanical Code, tightens ventilation and filtration rules
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Summary
HCAI senior engineer Larry Enright reviewed OSHPD amendments to the 2025 California Mechanical Code including a new OSHPD 6 designation, alignment with the 2021 ASHRAE 170 standard, reorganization of ventilation tables, and a move to locate HEPA filters at the room’s air-terminal device for certain critical spaces.
Larry Enright, senior mechanical engineer in the Department of Health Care Access and Information(HCAI) building standards unit under OSHPD, presented proposed OSHPD amendments to the 2025 California Mechanical Code during a public webinar.
Enright said the package adds a new OSHPD designation, OSHPD 6, to coordinate mechanical provisions for chemical dependency recovery hospitals with California Building Code function requirements. "This coordinates with the California building and administrative codes for chemical dependency, which, chemical dependency recovery hospitals," he said, introducing OSHPD 6 and noting that most OSHPD 6 requirements will fall under model code provisions.
A major focus of the amendments is ventilation and filtration. The draft revisions align many local amendments with the 2021 edition of ASHRAE 170 and reorganize table 4a and related footnotes to use California Building Code terminology and function callouts. Enright said the edits make clear that, where OSHPD and ASHRAE requirements conflict, "the most restrictive requirement shall prevail." The table rework also adds an "unoccupied turndown" column and adds OSHPD banners to identify which OSHPD category (1—6) each row applies to.
The package moves HEPA filtration requirements in some rooms to the air-terminal device (ATD) in the served space rather than relying on a third filter bank at the air-handler unit. "The air terminal device was also the new definition..." Enright said, explaining that operating rooms and protected-environment rooms that require HEPA will have that filtration at the ATD. He also noted the removal of MERV 17 from the tables, saying MERV 17 "doesn't quite meet the HEPA requirements," and that footnotes now call out HEPA testing methods and ATD placement.
Other technical changes include a new 3.21.3 provision to require cooling equipment needed to maintain temperature and humidity for operating rooms and spaces identified in the facility functional program; reorganized and clarified airflow and air-balance tolerances (including door pressure testing for airborne infection isolation rooms); recirculating room-unit requirements and minimum filtration (MERV 8 where applicable); and clarify coil design to avoid condensation risks on chilled beams.
Enright also described a new requirement for exhaust-discharge heights and separation distances from outdoor air intakes for infection-control spaces (bronchoscopy, compounding, morgues), and said the minimum AIIR (airborne infection isolation room) height was updated from 7 feet to 10 feet to match ASHRAE 170 (2021). He emphasized that testing and balancing will include pressure testing at doors to verify directional pressure and alarm requirements.
Enright closed Part 4 by noting that the package references updated national standards in chapter 18 (including the HEPA-filter standard) and that draft statements of reasons and other rulemaking documents are posted to the California Building Standards Commission rulemaking page and commission meeting records.
The webinar included attendee questions and clarifications about plan-review application of individual space controls, flexible-duct connector lengths, and coordination with the State Fire Marshal. Enright said questions and a written Q&A matrix will be posted on the HCAI website with the webinar recording and slide handout.
