407.4 Air Circulation — 2025 California Mechanical Code

407.4.1 Design of the ventilation system shall provide air movement that is generally from clean to less clean areas.

407.4.1.1 All air distribution devices and supply air outlets shall meet the requirements of ASHRAE 170, Section 6.7.2 and Table 6-2.

407.4.1.2 Supply outlets and return and exhaust air inlets shall be located to prevent short-circuiting.

407.4.1.3 Air supplied to operating rooms, cesarean operating rooms, cardiac catheterization labs, sur- gical cystoscopy rooms, delivery rooms, and class 3 imaging shall be delivered by a primary supply dif- fuser array in accordance with ASHRAE 170, 7.4.1.

407.4.1.4 Air supplied to procedure rooms and Class 2 imaging shall be delivered over the patient table. Return or exhaust inlets shall be located at the perimeter of the room on a minimum of two sides to provide air movement from clean to less clean.

407.4.1.5 At least two exhaust or recirculation air inlets of equal capacity shall be provided on oppo-

site corners in all operating rooms, cesarean oper- ating rooms, cardiac catheterization labs, surgical cystoscopy rooms, delivery rooms and class 3 imag- ing. All air inlets in the room shall be located not less than 3 inches (76 mm) nor more than 8 inches (203 mm) above the finished floor.

407.4.1.6 Morgues and autopsy rooms shall exhaust air through an autopsy table designed for this pur- pose or through low sidewall exhaust inlets located not less than 3 inches (76 mm) nor more than 8 inches (203 mm) above the finished floor.

407.4.1.7 Room supply air outlets and room recir- culation and exhaust air inlets installed in nonsensi- tive areas shall be located not less than 3 inches (76 mm) above the floor.

Exception: For airborne infection isolation rooms and protective environment rooms, see Sections 414.0 and 415.0.

407.4.2 Corridors shall not be used to convey supply, return, transfer or exhaust air to or from any room per the California Building Code.

Exceptions:

(1) Use of a corridor as a source of makeup air for exhaust systems in rooms that open directly onto such corridors is permitted where allowed by the Califor- nia Building Code. The corridor air balance shall be equal based on the total net transfer air to or from the corridor.

(2) Air transfer caused by pressure differentials in rooms required to have a positive or negative air balance by Table 4-A.

407.4.3 No space above a ceiling may be utilized as an outside-air, relief-air, supply-air, exhaust-air, or return- air plenum.

Exception: Designs specifically approved by the enforc- ing agency. 407.4.4 Air from a patient room, exam room, treatment room shall not be transferred to another similar room without first having passed through air filters as required by Table 4-B or Table 4-C. 407.4.5 Recirculating Room Units. Recirculating room units shall be permitted to provide a portion of the total air changes for a space in excess of the minimum outside air changes where indicated with a “yes” in the “Recirculated Room Units” column of Table 4-A. The fol- lowing conditions shall be met: (1) not receive nonfiltered, nonconditioned outdoor air; (2) shall serve only a single space; and (3) provide minimum MERV 8 filtration upstream of any surface that is designed to condense water. OSHPD 2 spaces shall be permitted to provide the manufac- turer’s recommended filter for airflow passing over any surface that is designed to condense water. (4) Coils designed not to condense water shall maintain surfaces above the dew point temperature.

407.4.5.1 Recirculating Room Units for Unoc- cupied Spaces. For normally unoccupied spaces not listed in Table 4-A and not directly connected to a patient care area, the minimum filtration for a recir- culating room unit may be as recommended by the equipment manufacturer.