CRSC · California Referenced Standards Code

What are the CRSC test apparatus, methods and classification requirements for air filters?

In plain terms: California’s CRSC **§ 12-71-100** mandates a standardized duct and burner setup, a 3‑minute flame test on clean filters with photoelectric smoke monitoring, and two classifications — **Class 1** (very low smoke; <1.5 in² and no downstream flames/sparks) or **Class 2** (moderate burning/smoke but not projecting igniting flames and ≤6.0 in²); adhesives used must have a high flash point.

Ask a question free See coverage

Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The State Fire Marshal’s standard in § 12-71-100 establishes the required test apparatus, test method, and classification rules for air filter units: a specifically dimensioned test duct and burner arrangement, a 3‑minute flame exposure of a clean (unused) filter, photoelectric measurement of smoke to compute an area under a curve, and two performance classes set by smoke-area and flame/spark behavior. All requirements and thresholds are set in § 12-71-100.

The single most important rule: test filters clean, expose them to the standardized flame and airflow setup for 3 minutes, then classify by whether flames/sparks travel downstream and by the measured area under the smoke-density curve. § 12-71-100

Requirements in detail

1) Test apparatus (what the lab must build)

Test duct: rectangular steel duct, 21 inches square and 13.5 feet (4114 mm) long, reinforced and fitted with a central metal filter frame sized to receive a 20 by 20 inch (nominal) filter unit. § 12-71-100(a)(1–2)
Blower and discharge: one end tapered to a variable-speed blower; the opposite end open to discharge. Mica windows in access doors allow observation of both faces and downstream conditions. § 12-71-100(a)(2)
Burner arrangement: two 1‑inch pipe elbows located ≈ 18 inches (457 mm) downstream from the filter base, producing yellow, wavering flames consuming about 4 cubic feet of gas per minute (approx. 1,000 Btu/ft3). § 12-71-100(a)(3)
Air velocity: with the filter in place, adjust to approximately 200 linear feet per minute measured at the duct discharge using an anemometer/velometer. § 12-71-100(a)(4)

2) Test method (how to run it)

Specimen condition: test filters clean (unused) only. § 12-71-100(b)(1)
Exposure interval: apply the flames for 3 minutes while observing both faces for downstream flame or sparks and noting density, duration and character of combustion products. § 12-71-100(b)(1)
Smoke measurement: a photoelectric cell and stabilized light source are mounted near the discharge end (cell about 12 inches inside discharge and light 1 inch above the duct). Record microammeter readings every 5 seconds during the first minute and every 10 seconds for the next 2 minutes. § 12-71-100(b)(2–3)
Data reduction: subtract pre-test readings, plot light-drop vs. time (scale specified in the standard) and measure the area under the curve (planimeter or calculation). That area = smoke density measure used for classification. § 12-71-100(b)(3)

3) Classification (how units are judged)

Class 1: When clean, no flames or sparks are produced downstream and the area under the smoke-density curve is less than 1.5 square inches. § 12-71-100(c)(1)
Class 2: When clean, units may burn moderately or emit moderate smoke, and though they may be consumed somewhat, they must not project flames or extensive sparks that would ignite combustibles beyond the discharge and their smoke-area must be not more than 6.0 square inches. § 12-71-100(c)(2)

4) Adhesives / coatings

Liquid-adhesive coatings on filters must have a flash point ≥ 325°F (163°C) as measured by the Cleveland open cup tester. § 12-71-100(d)

Quick reference table — decision‑relevant values

Parameter	Required value / action	Code Reference
Test duct cross-section	21 in. square	§ 12-71-100(a)(1)
Test duct length	13.5 ft (4114 mm)	§ 12-71-100(a)(1)
Test filter nominal size	20 × 20 in.	§ 12-71-100(a)(2)
Burner location	~18 in. from filter base; two 1‑in pipe elbows	§ 12-71-100(a)(3)
Burner gas consumption	~4 cu ft/min	§ 12-71-100(a)(3)
Air velocity during test	~200 ft/min	§ 12-71-100(a)(4)
Flame exposure duration	3 minutes	§ 12-71-100(b)(1)
Smoke reading intervals	every 5s (first min), every 10s (next 2 min)	§ 12-71-100(b)(2)
Class 1 smoke-area threshold	< 1.5 in²	§ 12-71-100(c)(1)
Class 2 smoke-area upper limit	≤ 6.0 in²	§ 12-71-100(c)(2)
Adhesive flash point	≥ 325°F (Cleveland open cup)	§ 12-71-100(d)

Exceptions & special cases

The standard explicitly applies to filters tested clean; used/loaded filters are not the test specimen under § 12-71-100(b)(1).
A product producing an area under the smoke curve greater than 6.0 in² is not within Class 2 per the stated limits — the standard defines Class 1 and Class 2 only up to that boundary; anything above the Class 2 limit exceeds the classification given in § 12-71-100(c).
Adhesive coatings have a separate thermochemical requirement (flash point) in § 12-71-100(d); a filter meeting flame/smoke criteria but using low‑flash adhesives would fail that adhesive requirement.

Common mistakes

Testing a dirty filter or not starting from “clean” condition (the standard requires unused specimens). § 12-71-100(b)(1)
Incorrect air velocity — the test requires about 200 ft/min at discharge; significant deviation invalidates comparability. § 12-71-100(a)(4)
Misplacing the photoelectric cell or light source (they must be at the distances specified) which changes the microammeter response and the computed area. § 12-71-100(b)(2–3)
Applying flames for the wrong duration (must be 3 minutes) or recording at wrong time intervals (every 5 s first minute / every 10 s next two minutes). § 12-71-100(b)(1–2)
Ignoring adhesive flash-point limits for liquid adhesives applied to the media (must be ≥ 325°F Cleveland open cup). § 12-71-100(d)

Worked example — concrete scenario

Scenario: A laboratory tests a nominal 20 × 20 in. pleated air filter, clean and unused, in the prescribed duct. They set air velocity to 200 ft/min, ignite the two burners (≈4 ft3/min each as required), and expose the filter to flames for 3 minutes. During the run the microammeter/light-drop readings (after subtraction of the pre-test baseline) are plotted and the measured area under the smoke-density curve is 2.0 square inches.

Does it project flames or extensive sparks beyond the discharge? — Observation: small localized burning on the downstream face but no projected flames or extensive sparks. (If it did project flames/sparks that could ignite adjacent combustibles, it would fail Class 2.) § 12-71-100(c)(2)
Smoke-area classification: 2.0 in² is greater than 1.5 in² (Class 1 limit) but ≤ 6.0 in² (Class 2 limit). Therefore the unit is classified Class 2 under § 12-71-100(c)(2).

If instead the area had been 1.2 in² and no projected flames/sparks, the unit would be Class 1. § 12-71-100(c)(1)

Related provisions (CRSC)

§ 12-71-100 — Air filters: test apparatus, method and classification (controlling section).
§ 12-7-103 — Classification reporting and required elements of fire exposure reports (relevant to how test results are reported).
§ 12-7-104 — Requirements for representative test specimens (applies generally to test specimen preparation).
§ 12-7-105 — Conduct and duration of tests for fire-resistive standards (general test-conduct guidance).
Chapter listing for 12-71 Air Filters (Chapter index in the CRSC).

(If you need the exact test-plotting scale, planimeter procedure, or verbatim measurement positions that the laboratory must follow, they are contained in the full text of § 12-71-100 and should be used as the authoritative procedure. )

Code references

Grounded in the retrieved California Referenced Standards Code — click a citation to read the verbatim passage:

CRSC § 12-71 High relevance — show source text
STATE FIRE MARSHAL

DESCRIPTION OF TEST APPARATUS, METHOD AND CLASSIFICATION REQUIREMENTS FOR AIR FILTERS

Sec. 12-71-100.

(a) Test apparatus.
1. The test duct, made of M.S. gage galvanized sheet metal reinforced with angle irons, is 21 inches square (13 548 mm [2] ) and 13 [1] / 2 feet (4114 mm) long.
2. One end of the duct is tapered to the discharge of a variable-speed blower and the other end is open to discharge. A metal filter frame is provided near the middle of the length of the duct to receive one 20 by 20 inches (508 mm by 508 mm) (nominal) filter unit. Two tightfitting doors, located to permit access to the filter frame, are each provided with a mica window to permit observation of both faces of the filter and conditions in the duct downstream from the filter.
3. Two 1-inch (25 mm) pipe elbows, about 18 inches (457 mm) from the base of the test filter, form gas burner outlets adjusted to provide yellow, wavering flames. The burners consume approximately 4 cubic feet (approximately 1,000 Btu/cubic feet) of gas per minute.
4. With the filter in place the air velocity is adjusted to approximately 200 linear feet per minute as measured at the discharge end of the duct by an Alnor Velometer Anemometer.
(b) Test method.
1. Filters are tested clean, that is, unused. The flames are applied for 3 minutes during which time observations are made of both faces of the filter as to the downstream travel of flame or sparks and the density, duration and character of the products of combustion.
2. Smoke density is measured as the drop in light intensity on a microammeter by means of photoelectric cell mounted a few inches below and about 12 inches (305 mm) inside the discharge end of the duct. The light source, stabilized for light intensity, is mounted 1 inch (25 mm) above the duct directly above the photoelectric cell. The microammeter readings are recorded every 5 seconds for the first minute and every 10 seconds for the next 2 minutes.
3. The differences between these readings and the readings taken before the test are plotted against time (the scale being 40 μA and 40 seconds to the inch) with the resulting area under the curve being measured by use of a planimeter or calculated mathematically. This area is a measure of the smoke density produced during the test.
(c) Classification. As a result of the tests, air filter units are classified as Class 1 or 2 as indicated below:
1. Class 1 air filter units are those which, when clean, do not produce flames or sparks when attacked by flame and which develop areas under the smoke density curves that are less than 1.5 square inches (967 mm [2] ).
2. Class 2 air filter units are those which, when clean, burn moderately when attacked by flame or emit moderate amounts of smoke or both. These units, although they may be consumed to some extent, do not project flames or extensive sparks that would ignite adjacent combustible materials beyond the discharge end of the duct during the test and do not develop areas under the smoke density curves that are more than 6.0 square inches (3871 mm [2] ).
(d) Adhesive coatings. Liquid-adhesive coatings used on filters shall have a flash point of 325°F (163°C) Cleveland open cup tester, or higher.
CRSC § 436.5. High relevance — show source text
DEPARTMENT OF HEALTH SERVICES

Authority: Sections 102, 208 and 25811.

Reference: Sections 102, 208 and 436.5.

ALL HEALING ARTS X-RAY INSTALLATIONS

Sec. 12-31C-101. All radiation shielding barriers in rooms and enclosures housing radiation machines shall comply with the mandatory standards and appendices in Report No. 35, “Dental X-RAY Protection”; Report 49, “Structural Shielding Design and Evaluation for Medical use of X-rays and Gamma Rays of Energies up to 10 MeV”; and Report No. 51, “Radiation Protection Design Guidelines for 0.1-100 MeV Particle Accelerator Facilities.” Published by the National Council on Radiation Protection and Measurements, 7910 Woodmont Avenue, Bethesda, Maryland 20814.

2025 CALIFORNIA REFERENCED STANDARDS CODE 105

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

106 2025 CALIFORNIA REFERENCED STANDARDS CODE

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

12-71 AIR FILTERS

STANDARD 12-71-1

STATE FIRE MARSHAL

DESCRIPTION OF TEST APPARATUS, METHOD AND CLASSIFICATION REQUIREMENTS FOR AIR FILTERS

Sec. 12-71-100.

(a) Test apparatus.
1. The test duct, made of M.S. gage galvanized sheet metal reinforced with angle irons, is 21 inches square (13 548 mm [2] ) and 13 [1] / 2 feet (4114 mm) long.
2. One end of the duct is tapered to the discharge of a variable-speed blower and the other end is open to discharge. A metal filter frame is provided near the middle of the length of the duct to receive one 20 by 20 inches (508 mm by 508 mm) (nominal) filter unit. Two tightfitting doors, located to permit access to the filter frame, are each provided with a mica window to permit observation of both faces of the filter and conditions in the duct downstream from the filter.
3. Two 1-inch (25 mm) pipe elbows, about 18 inches (457 mm) from the base of the test filter, form gas burner outlets adjusted to provide yellow, wavering flames. The burners consume approximately 4 cubic feet (approximately 1,000 Btu/cubic feet) of gas per minute.
4. With the filter in place the air velocity is adjusted to approximately 200 linear feet per minute as measured at the discharge end of the duct by an Alnor Velometer Anemometer.
(b) Test method.
1. Filters are tested clean, that is, unused. The flames are applied for 3 minutes during which time observations are made of both faces of the filter as to the downstream travel of flame or sparks and the density, duration and character of the products of combustion.
CRSC § 1.5 High relevance — show source text
1. Smoke density is measured as the drop in light intensity on a microammeter by means of photoelectric cell mounted a few inches below and about 12 inches (305 mm) inside the discharge end of the duct. The light source, stabilized for light intensity, is mounted 1 inch (25 mm) above the duct directly above the photoelectric cell. The microammeter readings are recorded every 5 seconds for the first minute and every 10 seconds for the next 2 minutes.
2. The differences between these readings and the readings taken before the test are plotted against time (the scale being 40 μA and 40 seconds to the inch) with the resulting area under the curve being measured by use of a planimeter or calculated mathematically. This area is a measure of the smoke density produced during the test.
(c) Classification. As a result of the tests, air filter units are classified as Class 1 or 2 as indicated below:
1. Class 1 air filter units are those which, when clean, do not produce flames or sparks when attacked by flame and which develop areas under the smoke density curves that are less than 1.5 square inches (967 mm [2] ).
2. Class 2 air filter units are those which, when clean, burn moderately when attacked by flame or emit moderate amounts of smoke or both. These units, although they may be consumed to some extent, do not project flames or extensive sparks that would ignite adjacent combustible materials beyond the discharge end of the duct during the test and do not develop areas under the smoke density curves that are more than 6.0 square inches (3871 mm [2] ).
(d) Adhesive coatings. Liquid-adhesive coatings used on filters shall have a flash point of 325°F (163°C) Cleveland open cup tester, or higher.

2025 CALIFORNIA REFERENCED STANDARDS CODE 107

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

108 2025 CALIFORNIA REFERENCED STANDARDS CODE

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

12-72-1 PROTECTIVE SIGNALING SYSTEMS

STANDARD TEST PROCEDURES

STANDARD 12-72-1

STATE FIRE MARSHAL

SCOPE

Sec. 12-72-100.

(a) Basic. This standard represents the minimum basic requirements for the construction and performance of the protective signaling systems to be listed under this classification. The minimum design, construction and performance standards set forth herein are those deemed as minimum necessary to establish conformance to the regulations of the State Fire Marshal as set forth in the California Electrical Code, and when applicable shall be reported on in their entirety by the approved testing laboratory.

(b) Systems. This standard covers electrically operated devices and control units designed to transmit and sound alarms, supervisory and trouble signals to be employed in ordinary indoor locations in accordance with the Standards of the National Fire Protection Association for the Installation, Maintenance and Use of Proprietary, Auxiliary and Local Protective Signaling Systems, Remote Station, Nos. 72A, 72B, 72C and 72D, and the California Electrical Code. This includes combination protective signaling systems employing nonsupervised sounding circuits; combination fire alarm-communication, -program and -clock systems (hereinafter referred to as combination signaling systems); and audible devices used for both alarm and program or communication

purposes.
CRSC § 12-7 Medium relevance — show source text
12-7A-4.8 PART B. Burning brand exposure.

12-7A-4.8.1 Equipment.
1. Wind tunnel. The wind tunnel shall have the capability of providing 12 mph (5.4 m/s) airflow over the deck assembly.
2. Anemometer. Device for measuring airflow across the deck.
3. Burner. Gas-fueled burner for brand ignition.
12-7A-4.8.2 Test system preparation. See Figure 2. The ASTM E108 “A” brand roof test apparatus is to be used, with the following modifications:
1. Deck support. The deck shall be supported horizontally with the center 60 inches (150 mm) from the front opening of the wind tunnel and the joists parallel to the airflow and resting on two transverse metal supports. The top surfaces of these supports, no more than 3 inches (75 mm) wide, are at the same height as the floor of the wind tunnel.
2. Fragments. Burning fragments shall be free to fall to the floor of the room.
12-7A-4.8.3 Conduct of tests.
1. Number of tests. Conduct the test on three replicate assemblies.
2. Moisture content. Measure the moisture content of the wooden members of the assembly using a moisture meter (ASTM D4444).
3. Procedure. Adhere to ASTM E108 “Standard Test Methods for Fire Tests of Roof Coverings” (burning brand test, “A” brand), with apparatus modified as described above in “Test system preparation” and the following procedure: 3.1. The air velocity shall be calibrated using the 60-inch (1.5 m) framework spacing, with a smooth noncombustible calibration deck at a 5-inch (127 mm) per 12-inch (305 mm) horizontal incline positioned 60 inches (1.5 m) from the front opening of the wind tunnel. All other measurement details shall be followed as specified in Sections 4.4.2, 4.4.3 and 4.4.4 of ASTM E108. Although ASTM E108 specifies calibration to be conducted with the 33-inch (840-mm) framework spacing used for the intermittent flame test set up, tests have shown that at the nominal 12 mph
46 2025 CALIFORNIA REFERENCED STANDARDS CODE

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

MATERIALS AND CONSTRUCTION METHODS FOR EXTERIOR WILDFIRE EXPOSURE

setting, there was not difference in measured velocity between the 33- and 60-inch (838 mm and 1524 mm) framework spacing. 3.2. Mount the test specimen at a zero horizontal incline positioned 60 inches (1.5 m) from the front opening of the wind tunnel.

3.3. Ignite the “A” brands as specified in Section 9.4 of ASTM E108 as reprinted here:
1. Each 12- x 12-inch (300 x 300 mm) face for 30 seconds.
2. Each 2.25- x 12-inch (57 x 300 mm) edge for 45 seconds.
3. Each 12- x 12-inch (300 x 300 mm) face again for 30 seconds. 3.4. Center the burning brand laterally on the deck with the front edge 2.5 inches (64 mm) from the entering air edge of the deck.
CRSC § 12-16 Medium relevance — show source text
CALIFORNIA STANDARD FOR RESIDENTIAL EXCESS FLOW ACTUATED AUTOMATIC GAS SHUTOFF VALVES (SEE CCR TITLE 24, PART 5, CHAPTER 12) STANDARD 12-16-2

DIVISION OF THE STATE ARCHITECT

Authority: Sections 19200–19204, Health and Safety Code. Reference: Sections 19201.5 and 19202, Health and Safety Code.

DIVISION 1—CONSTRUCTION

SCOPE

Sec. 12-16-201. The American Society for Testing and Materials (ASTM) F2138-12(2017) Standard Specification for Excess Flow Valves for Natural Gas Service, and the American National Standards Institute (ANSI) Z21.93-2017/CSA 6.30-2017 Excess Flow Valves for Natural and LP Gas with Pressure up to 5 psig, shall be the applicable standards used by the Division of the State Architect for certification of these devices.

Sec. 12-16-201.1. Each installation of a customer-owned device that satisfies this standard shall be in accordance with the California Plumbing Code (CCR Title 24, Part 5).

2025 CALIFORNIA REFERENCED STANDARDS CODE 103

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

104 2025 CALIFORNIA REFERENCED STANDARDS CODE

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

12-31C RADIATION SHIELDING STANDARDS

STANDARD 12-31C-1

DEPARTMENT OF HEALTH SERVICES

Authority: Sections 102, 208 and 25811.

Reference: Sections 102, 208 and 436.5.

ALL HEALING ARTS X-RAY INSTALLATIONS

Sec. 12-31C-101. All radiation shielding barriers in rooms and enclosures housing radiation machines shall comply with the mandatory standards and appendices in Report No. 35, “Dental X-RAY Protection”; Report 49, “Structural Shielding Design and Evaluation for Medical use of X-rays and Gamma Rays of Energies up to 10 MeV”; and Report No. 51, “Radiation Protection Design Guidelines for 0.1-100 MeV Particle Accelerator Facilities.” Published by the National Council on Radiation Protection and Measurements, 7910 Woodmont Avenue, Bethesda, Maryland 20814.

2025 CALIFORNIA REFERENCED STANDARDS CODE 105

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

106 2025 CALIFORNIA REFERENCED STANDARDS CODE

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

12-71 AIR FILTERS

STANDARD 12-71-1

STATE FIRE MARSHAL

DESCRIPTION OF TEST APPARATUS, METHOD AND CLASSIFICATION REQUIREMENTS FOR AIR FILTERS

Sec. 12-71-100.

(a) Test apparatus.
1. The test duct, made of M.S. gage galvanized sheet metal reinforced with angle irons, is 21 inches square (13 548 mm [2] ) and 13 [1] / 2 feet (4114 mm) long.
CRSC § 203.0 Medium relevance — show source text
Readily, definition . . . . . . . . . . . . . . . . . . . . . . . . . 203.0

ACCESSORY DWELLING UNIT

Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0

ADMINISTRATION

California . . . . . . . . . . . . . . . . . . . . Chapter 1, Division I

General . . . . . . . . . . . . . . . . . . . . . Chapter 1 , Division II

AIR

Balancing . . . . . . . . . . . . . 314.0, 403.10, 407.3, 511.3.1,

E 503.3.1, E 503.6.5.3,

E 605.1.5, E 803.2

Circulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407.4

Classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403.9

Combustion . . . . . . . . . . . . . . . . . (see Combustion Air)

Dilution . . . . . . . . . . . . . . . . . . . . . . . 203.0, Table 403.7,

701.1, 701.1.1, 701.8, 701.10,

802.6.3.1, 902.2, 902.12, 902.13

Ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (see Ducts) Economizer . . . . . . . . . . . . . . . . . (see Economizer, air) Exhaust . . . . . . . . . . . . . . . . . . . . . . . (see Air, exhaust) Filters. . . . . . . . . . . . . . . . . . . . . . . . . . . (see Filters, air) Furnace . . . . . . . . . . . . . . . . . (see Furnaces, warm air) Heaters. . . . . . . . . . . . . . . . . . . . . . . . . (see Heater, air)

Makeup . . . . . . . . . . . . . . . 203.0, 401.1, 403.7, 504.4.1,

505.10, 511.3, 517.1.2, 517.1.3,

517.6.1, 517.6.2, 519.6, 701.1,

701.3, 930.5.4, 1106.2.8, 1106.6,

1106.11.11.1, 1220.5, E 503.4.6.9,

E 503.5.11.3, I 801.1.4
CRSC § 903.2 Medium relevance — show source text
Gas fired type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.2

General requirements . . . . . . . . . . . . . . . . . . Chapter 3

Refrigerant port protection . . . . . . . . . . . . . . . . . 1105.11

System test . . . . . . . . . . . . . . . . . . . . . . . . . . . . E 805.0

System water use . . . . . . . . . . . . . . . . . . . . . . . E 403.0

AIR-HANDLING UNIT

Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0

Ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 6

Exposed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904.9.1

Permit Fees . . . . . . . . . . . . . . . . . . . . . . . . . Table 104.5

System test . . . . . . . . . . . . . . . . . . . . . . . . . . . . E 805.0

AIR, EXHAUST

Cross Contamination. . . . . . . . . . . . . . . . . . . . . . 603.10

Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0

Grease filters. . . . . . . . . . . . . . . . . . . . . . . . . . 509.2.3.1

Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305.3.2

Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403.7

Volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511.2.2

AIR RELIEF

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0

AIR TERMINAL DEVICE

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0

ALARMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416.0, 418.5

ALTERNATE MATERIALS AND METHODS

CONSTRUCTION EQUIVALENCY . . . . . . . . . . . . . . 302.2

ALTERNATIVE ENGINEERING DESIGN
CRSC § 601.0 Medium relevance — show source text
136 2025 CALIFORNIA MECHANICAL CODE

), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

CHAPTER 6

DUCT SYSTEMS

601.0 General.

601.1 Applicability. Ducts and plenums that are portions of a heating, cooling, ventilation, or exhaust system shall comply with the requirements of this chapter, Chapter 5 for exhaust ducts, and Chapter 7 for combustion air ducts. 601.2 Sizing Requirements. Duct systems shall be sized in accordance with applicable standards in Chapter 18 or by other approved methods.

Exception: Residential duct systems shall be sized in accordance with ACCA Manual D, ACCA Manual Zr, as applicable, or by other approved methods.

601.2.1 California Energy Code Residential Return Duct Sizing Requirements. California Energy Code Tables 150.0-B and 150.0-C specify return duct sizing requirements for single return and multiple return duct systems, respectively, that are applicable as an alternative to confirming system airflow via field verification and diagnostic testing. See California Energy Code Section 150.0(m)13 for provisions applicable to newly con- structed buildings, and Section 150.2(b)(1)(F)(ii)(a) for alterations.

602.0 Material.

602.1 General. Materials used for duct systems shall comply with Section 602.2 through Section 602.7 as applicable. Exception: [OSHPD 1, 1R, 2, 3, 4 & 5] See Section 407.4.2.

[Not permitted for OSHPD 1, 1R, 2, 3, 4 & 5] Concealed building spaces or independent construction within buildings shall be permitted to be used as ducts or plenums. Gypsum board shall not be used for positive pressure ducts.

Exception: In healthcare facilities, concealed spaces shall not be permitted to be used as ducts or plenums.

602.2 Combustibles Within Ducts or Plenums. Materials exposed within ducts or plenums shall be noncombustible or shall have a flame spread index not to exceed 25 and a smoke-developed index not to exceed 50, where tested as a composite product in accordance with ASTM E84 or UL 723. Plastic piping installed in plenums shall be tested in accordance with all requirements of ASTM E84 or UL 723. Mounting methods, supports and sample sizes of materials for testing that are not specified in ASTM E84 or UL 723 shall be prohibited.

Exceptions:

(1) Return-air and outside-air ducts, plenums, or concealed spaces that serve a dwelling unit.

(2) Air filters in accordance with the requirements of Section 311.2.

(3) Water evaporation media in an evaporative cooler.

(4) Charcoal filters where protected with an approved fire suppression system.

(5) Products listed and labeled for installation within plenums in accordance with Section 602.2.1 through Section 602.2.4.

(6) Smoke detectors in accordance with the requirements of Section 609.0.

(7) Duct insulation, coverings, and linings and other supplementary materials installed in accordance with Section 605.0.
CRSC § 12-7 Medium relevance — show source text
(d) Temperature intervals. Temperature readings shall be taken at intervals not exceeding 15 minutes until a reading exceeding 212°F (100°C) has been obtained at any one point. Thereafter the readings may be taken more frequently at the discretion of the testing body, but the intervals need not be less than 5 minutes.

(e) Maximum unexposed temperature rise. Where the conditions of acceptance place a limitation on the rise of temperature of the unexposed surface, the temperature end point of the fire endurance period shall be determined by the average of the measurements taken at individual points; except that if a temperature rise 30 percent in excess of the specified limit occurs at any one of these points, the remainder shall be ignored and the fire endurance period judged as ended.

CLASSIFICATION AS DETERMINED BY TEST

Sec. 12-7-103.

(a) Fire exposure report. Results shall be reported in accordance with the performance tests prescribed in these methods. They shall be expressed in time periods of resistance, to the nearest integral minute. Reports shall include observations of significant details of behavior of the material or construction during the test and after the furnace fire is cut off, including information on defor

2025 CALIFORNIA REFERENCED STANDARDS CODE 13

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

FIRE-RESISTIVE STANDARDS

mation, spalling, cracking, burning of the specimen or its component parts, continuance of flaming and production of smoke. The form and contents of reports shall be in accordance with Section 12-7-115.

(b) Structural fire report. Reports of tests involving wall, ceiling-floor, ceiling-roof or beam constructions in which restraint is provided against expansion, contraction or rotation of the construction shall describe the method used to provide this restraint and include details of the restraining frame as well as information recorded during the test concerning the forces imposed on that structure by the test specimen.

TEST SPECIMEN

Sec. 12-7-104.

(a) Representative specimen. The test specimen shall be truly representative of the construction for which classification is desired, as to materials, workmanship and details such as dimensions of parts, and shall be built under conditions representative of those obtaining as practically applied in building construction and operations. The physical properties of the materials and ingredients used in the test specimen shall be determined and recorded. When necessary for evaluation of test reports, the sponsor shall furnish them to the enforcing agency.

(b) Specimen size. The size and dimensions of the test specimen specified herein are intended to apply for rating constructions of dimensions within the usual general range employed in buildings. If the conditions of use limit the construction to smaller dimensions, a proportionate reduction may be made in the dimensions of the specimens for a test qualifying them for such restricted use.

DURATION AND CONDUCT OF TESTS

Sec. 12-7-105.

(a) Fire endurance. The fire endurance test on the specimen with its applied load, if any, shall be continued until failure occurs, or until the specimen has withstood the test conditions for a period equal to that herein specified in the conditions of acceptance for the given type of construction.
CRSC § 6.1507 Medium relevance — show source text
LIFT = Entering Condenser Water Temperature (°F) – Leaving Chilled Water Temperature (°F)
2. Condenser DT = Leaving Condenser Water Temperature (°F) – Entering Condenser Water Temperature (°F)
Kadj = 6.1507 – 0.30244(×) + 0.0062692(×)2 – 0.000045595(×)3
where× = Condenser DT + LIFT
COPadj = Kadj * COPstd|1. LIFT = Entering Condenser Water Temperature (°F) – Leaving Chilled Water Temperature (°F)
2. Condenser DT = Leaving Condenser Water Temperature (°F) – Entering Condenser Water Temperature (°F)
Kadj = 6.1507 – 0.30244(×) + 0.0062692(×)2 – 0.000045595(×)3
where× = Condenser DT + LIFT
COPadj = Kadj * COPstd|1. LIFT = Entering Condenser Water Temperature (°F) – Leaving Chilled Water Temperature (°F)
2. Condenser DT = Leaving Condenser Water Temperature (°F) – Entering Condenser Water Temperature (°F)
Kadj = 6.1507 – 0.30244(×) + 0.0062692(×)2 – 0.000045595(×)3
where× = Condenser DT + LIFT
COPadj = Kadj * COPstd|1. LIFT = Entering Condenser Water Temperature (°F) – Leaving Chilled Water Temperature (°F)
2. Condenser DT = Leaving Condenser Water Temperature (°F) – Entering Condenser Water Temperature (°F)
Kadj = 6.1507 – 0.30244(×) + 0.0062692(×)2 – 0.000045595(×)3
where× = Condenser DT + LIFT
COPadj = Kadj * COPstd|1. LIFT = Entering Condenser Water Temperature (°F) – Leaving Chilled Water Temperature (°F)
2. Condenser DT = Leaving Condenser Water Temperature (°F) – Entering Condenser Water Temperature (°F)
Kadj = 6.1507 – 0.30244(×) + 0.0062692(×)2 – 0.000045595(×)3
where× = Condenser DT + LIFT
COPadj = Kadj * COPstd|1. LIFT = Entering Condenser Water Temperature (°F) – Leaving Chilled Water Temperature (°F)
2. Condenser DT = Leaving Condenser Water Temperature (°F) – Entering Condenser Water Temperature (°F)
Kadj = 6.1507 – 0.30244(×) + 0.0062692(×)2 – 0.000045595(×)3
where× = Condenser DT + LIFT
COPadj = Kadj * COPstd|

A6.207.1.2 Controls for heat pumps with supplementary electric resistance heaters. Heat pumps with supplementary electric resistance heaters shall have controls:

A6.207.1.2.1 That prevent supplementary heater operation when the heating load can be met by the heat pump alone; and
CRSC § 150.0 Medium relevance — show source text
SINGLE-FAMILY RESIDENTIAL BUILDINGS— MANDATORY FEATURES AND DEVICES

iii. The supply side of mechanical balanced ventilation systems, including heat recovery ventilation systems, and energy recovery ventilation systems that provide outside air to an occupiable space. Exception 1 to Section 150.0(m)12A: Evaporative coolers are not required to comply with the air filtration requirements in Section 150.0(m)12.

B. System design and installation. i. The system shall be designed to ensure that all recirculated air and all outdoor air supplied to the occupiable space is filtered before passing through any system’s thermal conditioning components. Exception 1 to Section 150.0(m)12Bi: For heat recovery ventilators and energy recovery ventilators the location of the filters required by Section 150.0(m)12 may be downstream of a system thermal conditioning component, provided the system is equipped with ancillary filtration upstream of the system’s thermal conditioning component. ii. All systems shall be designed to accommodate the clean-filter pressure drop imposed by the system air filter(s). The design airflow rate and maximum allowable clean-filter pressure drop at the design airflow rate applicable to each air filter shall be determined and reported on labels according to Subsection iv below. Systems specified in Section 150.0(m)12Ai shall be equipped with air filters that meet either Subsection a or b below. a. Nominal two-inch minimum depth filter(s) shall be sized by the system designer, or b. Nominal one-inch minimum depth filter(s) shall be allowed if the filter(s) are sized according to Equation 150.0-A, based on a maximum face velocity of 150 ft per minute, and according to the maximum allowable clean-filter pressure drop specified in Section 150.0(m)12Dii. (Equation 150.0-A) A face = Q filter / V face

where

A face = air filter face area, the product of air filter nominal length x nominal width, ft [2] . Q filter = design airflow rate for the air filter, ft [3] /min. V face = air filter face velocity ≤ 150, ft/min. iii. All system air filters shall be located and installed in such a manner as to be accessible for regular service by the system owner. iv. All system air filter installation locations shall be labeled to disclose the applicable design airflow rate and the maximum allowable clean-filter pressure drop. The labels shall be permanently affixed to the air filter installation location, readily legible, and visible to a person replacing the air filter. v. Filter racks or grilles shall use gaskets, sealing or other means to close gaps around inserted filters to and prevent air from bypassing the filter. C. Air filter efficiency. The system shall be provided with air filter(s) having a designated efficiency equal to or greater than MERV 13 when tested in accordance with ASHRAE Standard 52.2, or a particle size efficiency rating equal to or greater than 50 percent in the 0.30 – 1.0 μm range, and equal to or greater than 85 percent in the 1.0 – 3.0 μm range when tested in accordance with AHRI Standard 680.

D. **Air filter pressure drop.

CRSC § 1.8 Medium relevance — show source text

Liquid line pressure
 Return air relative humidity
 Outside air temp
| |

j.
The controller will provide system status by indicating the following conditions:
 Compressor enabled
 Economizer enabled
 Free cooling available
 Heating enabled
 Mixed air low limit cycle active

~~Y / N~~|~~Y / N~~| |
k.
The unit controller shall have the capability to manually initiate each operating mode so that the operation
of compressors, economizers, fans, and heating system can be independently tested and verified.|Y / N|

For SI units: °C = (°F-32)/1.8

520 2025 CALIFORNIA MECHANICAL CODE

), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

APPENDIX E

CERTIFICATE OF ACCEPTANCE MECH-12A	Col2
Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion Units (Page 3 of 3)	Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion Units (Page 3 of 3)
Project Name/Address:	Project Name/Address:
System Name or Identification/Tag:	System Location or Area Served:

B. Functional Testing.	Col2	Results
Step 1: Low airflow test.	Step 1: Low airflow test.
a. Test low airflow condition by replacing the existing filter with a dirty filter or appropriate obstruction.	a. Test low airflow condition by replacing the existing filter with a dirty filter or appropriate obstruction.	a. Test low airflow condition by replacing the existing filter with a dirty filter or appropriate obstruction.
b. Verify that the fault detection and diagnostics system reports the fault.	b. Verify that the fault detection and diagnostics system reports the fault.	~~Y / N~~
c. Verify that the system is able to verify the correct refrigerant charge.	c. Verify that the system is able to verify the correct refrigerant charge.	Y / N
d. Verify that you are able to calibrate the following:  Outside Air Temperature Sensor.  Return Air Temperature Sensors.  Supply Air Temperature Sensors. ~~Y / N~~	d. Verify that you are able to calibrate the following:  Outside Air Temperature Sensor.  Return Air Temperature Sensors.  Supply Air Temperature Sensors. ~~Y / N~~	~~Y / N~~
C. Testing Results	PASS / FAIL	PASS / FAIL
Test passes if all answers are yes underEligibility Criteria andFunctional Testing.		

Frequently asked questions

What specimen condition is required for the test?

The filters must be clean (unused) when tested; the standard explicitly requires testing clean specimens. § 12-71-100(b)(1)

How long is the flame exposure?

Flames are applied for 3 minutes while observations and smoke measurements are made. § 12-71-100(b)(1–2)

What smoke-area values determine Class 1 vs Class 2?

Class 1: area under the smoke-density curve < 1.5 in². Class 2: area ≤ 6.0 in² and no projecting flames/extensive sparks beyond the duct discharge. § 12-71-100(c)

Do adhesive coatings have a requirement?

Yes — liquid-adhesive coatings must have a Cleveland open cup flash point ≥ 325°F (163°C). § 12-71-100(d)

What happens if a filter produces > 6.0 in² smoke-area?

That exceeds the Class 2 upper limit in § 12-71-100(c); such performance is outside the two-class definitions provided in the section and would not qualify as Class 1 or Class 2 under this standard.

More in California Referenced Standards Code

Ask about the CRSC

Get cited, plain-English answers on the California Referenced Standards Code for your project — any code section, any scenario.

Start Free Trial

Related in the CRSC

Which CRSC chapters cover protective signaling system standards and tests?

How does Part 12 cross-reference air/HVAC/filter standards to Title 24 requirements?

HVAC, Air Filters & Protective Signaling Standards

California Referenced Standards Code