CRC · California Residential Code
Direct-vent, integral-vent and mechanical draft appliance rules
The California Residential Code requires listed direct‑vent and integral‑vent appliances be installed per their manufacturer instructions (see § 509.2.6 and § 509.2.7) and mandates that mechanical draft systems be listed to UL 378, prevent flue‑gas leakage when under positive pressure, not accept natural‑draft connectors into positively pressurized portions, and include a means to stop gas flow if the draft fails (see § 509.3.3) .
Last reviewed: July 6, 2026
What the code requires — plain English
- Listed direct‑vent appliances must be installed exactly per the manufacturer’s installation instructions; through‑the‑wall terminations for direct‑vent units must follow the specific through‑wall termination rules referenced by the code (§ 509.2.6, § 509.2.6.1) .
- Appliances that include integral venting must be installed in accordance with the code section called out for integral vents (§ 509.2.7) .
- Mechanical draft systems (forced or induced draft) must be listed to UL 378 and installed per both the appliance and the mechanical‑draft manufacturer’s instructions; they must be designed to prevent leakage of flue gases into the building when any portion operates under positive pressure, and natural‑draft vent connectors must not tie into a positively pressurized mechanical draft portion (§ 509.3.3 and subsections) .
The single most important rule: follow the appliance and vent‑system manufacturers’ instructions — the code defers to those listings and instructions for direct‑vent, integral‑vent and mechanical‑draft installations. See § 509.2.6, § 509.2.7, § 509.3.3.
Requirements in detail
Key defined terms (first use is bolded)
- Direct‑vent appliance — a listed appliance that draws combustion air from the outdoors and exhausts to the outdoors through a sealed, listed system; the CRC requires installation per the appliance listing and manufacturer instructions (§ 509.2.6) .
- Appliance with integral vent — an appliance that includes its own venting means; installation must follow the code section for integral vents (§ 509.2.7) and the listed installation provisions found there .
- Mechanical draft systems — forced or induced draft venting systems that use fans; they must be listed to UL 378 and installed per both appliance and draft‑system manufacturers’ instructions (§ 509.3.3) .
- Positive pressure — any portion of an induced/forced draft system under pressure that could push flue gases into the building; the code requires those portions be installed to prevent leakage (§ 509.3.3.2) .
Decision‑relevant dimensions / values (quick reference)
| Decision item | Required action / value | Code reference |
|---|---|---|
| Installation of listed direct‑vent appliance | Install per the appliance listing and the manufacturer’s installation instructions | § 509.2.6 |
| Through‑the‑wall terminations for direct‑vent | Follow the through‑wall termination rules referenced in code (see § 509.8.1) | § 509.2.6.1 / § 509.8.1 |
| Appliances with integral vents | Install in accordance with the integral‑vent provisions in the code (Section 509.8) | § 509.2.7 |
| Mechanical draft listing | Mechanical draft systems must be listed in accordance with UL 378 | § 509.3.3 |
| Permitted draft types | Both forced and induced draft designs are permitted | § 509.3.3.1 |
| Leakage protection | Parts under positive pressure must be designed/installed to prevent leakage of flue/vent gases into the building | § 509.3.3.2 |
| Mixing vent connectors | Vent connectors from natural‑draft appliances must not be connected into mechanical draft portions operating under positive pressure | § 509.3.3.3 |
| Draft failure interlock | When a mechanical draft is used, there must be a way to prevent gas flow to main burners if the draft system is not performing to appliance requirements | § 509.3.3.4 |
How the three provisions interact
- § 509.2.6 (direct vent) and § 509.2.7 (integral vent) primarily require compliance with manufacturer instructions and with referenced through‑wall rules; the code does not restate every termination or clearance numeric in those paragraphs but points you to the manufacturer and to the code’s through‑wall/termination sections for details .
- § 509.3.3 imposes additional safety and listing requirements for mechanical draft systems (UL 378, leakage prevention, connector separation and interlock) — these are performance and installation obligations separate from the direct‑vent/integral‑vent rule and must be met in addition to following manufacturer instructions .
Exceptions & special cases
- The code text for § 509.2.6 and § 509.2.7 defers to manufacturers and to section 509.8/509.8.1 for through‑the‑wall clearances/terminations; if you need the numeric through‑wall clearances you must consult § 509.8.1 (that text was referenced by the code) — the relevant through‑wall numeric table is not reproduced here and must be consulted directly in § 509.8.1 .
- Where a mechanical draft system has any portion under positive pressure, that portion must be sealed/designed to prevent leakage — that is mandatory (no exception given) per § 509.3.3.2 .
- The code permits both forced and induced draft mechanical systems, but they must be listed and installed per UL 378 and manufacturer instructions — do not assume an unlisted fan‑assisted arrangement is code‑compliant (§ 509.3.3, § 509.3.3.1) .
If you need the specific through‑wall clearance table or termination heights, consult § 509.8.1 and § 509.6.1 (termination) in the code — those sections contain numeric values and figures that were referenced but are not reproduced in the controlling clauses cited here .
Common mistakes
- Relying on “reasonable” installation instead of following the appliance manufacturer’s instructions or the exact listing (direct‑vent and integral‑vent installations are explicitly tied to the appliance instructions — § 509.2.6 and § 509.2.7) .
- Connecting a natural‑draft appliance’s vent connector into a mechanical draft system portion that operates under positive pressure — the code forbids this (§ 509.3.3.3) .
- Failing to provide sealed joints or design to prevent leakage where the mechanical draft system is under positive pressure; unsealed joints can allow flue gas into occupied space (§ 509.3.3.2) .
- Assuming any fan added to a vent is acceptable — mechanical draft systems must be listed to UL 378 and installed per manufacturer instructions (§ 509.3.3) .
Worked example — applying the rules (concrete scenario)
Scenario: You are replacing a gas water heater in a single‑family home with a new listed unit that is a manufacture‑supplied induced‑draft (fan‑assisted) model with an integral vent adapter and a through‑the‑wall termination.
Steps to comply:
- Confirm the appliance is listed and follow the appliance manufacturer’s installation instructions for the integral vent and termination. The code requires listed direct‑vent and integral‑vent appliances be installed per their instructions (§ 509.2.6, § 509.2.7) .
- Because the unit uses an internal fan (mechanical draft), confirm the mechanical draft system components (fan/adapter/assemblies) are listed to UL 378 and install the draft system per both the appliance and mechanical draft manufacturer instructions as required by § 509.3.3 .
- If any portion of the draft path operates under positive pressure (typical for forced‑draft segments), install the sections and joints so they prevent leakage of flue gases into the building (seal, gasketed connections, listed components) as required by § 509.3.3.2 .
- Do not connect any existing natural‑draft appliance vent connectors into the new mechanical draft assembly if that mechanical portion will operate under positive pressure; the code forbids that connection (§ 509.3.3.3) .
- Provide the required interlock/protection so that gas to the main burner is blocked if the mechanical draft is not operating per the appliance’s safe‑operation requirements (fan failure interlock or similar) per § 509.3.3.4 .
- For the through‑the‑wall termination, follow the through‑wall termination provisions referenced by the direct‑vent/integral‑vent rules (the code points to § 509.8.1 for through‑the‑wall terminations) — consult that section for numeric clearances and orientation details .
Result: If you can show the appliance is listed and installed per appliance and draft listings, all joints and positive‑pressure segments are sealed, natural‑draft connectors are isolated, and a fan‑failure interlock is provided, you will meet the specific obligations of § 509.2.6, § 509.2.7, and § 509.3.3 documented above .
Related provisions (quick links to code sections)
- § 509.8 / § 509.8.1 — through‑the‑wall termination and clearance details referenced by §§ 509.2.6 and 509.2.7 (see the code text referenced by the direct‑vent/integral‑vent rules) .
- § 509.6.1 — gas vent termination locations and general termination requirements (the code cross‑references mechanical draft and direct‑vent terminations here) .
- § 509.3.1 – § 509.3.2 — minimum safe performance and appliance venting connection requirements (appliance draft and venting system design obligations referenced by § 509.3.3) .
- § 509.4 – § 509.15 — broader venting system design and installation rules, sizing and materials (ties into appliance vent selection and permitted materials) .
- Index entries and cross references for direct‑vent, integral, and mechanical draft in the code index (see code index entries) .
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 802.2.5. High relevance — show source text
(b) Gas vents that are over 12 inches (300 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall
terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above a portion of a building within 10 feet (3048 mm) horizontally.
(c) Industrial appliances as provided in Section 802.2.5.
(d) Direct vent systems as provided in Section 802.2.6.
(e) Appliances with integral vents as provided in Section 802.2.7.
(f) Mechanical draft systems as provided in Section 802.3.3 through Section 802.3.3.4.
(g) Ventilating hoods and exhaust systems as provided in Section 802.3.4.
(2) A Type B or a Type L gas vent shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar.
(3) A Type B-W gas vent shall terminate at least 12 feet (3658 mm) in vertical height above the bottom of the wall furnace.
(4) A gas vent extending through an exterior wall shall not terminate adjacent to the wall or below eaves or parapets, except as provided in Section 802.2.6 and Section 802.3.3 through Section 802.3.3.4.
(5) Decorative shrouds shall not be installed at the termination of gas vents except where such shrouds are listed for use with the specific gas venting system and are installed in accordance with the manufac turer’s installation instructions.
(6) All gas vents shall extend through the roof flashing, roof jack, or roof thimble and terminate with a listed cap or listed roof assembly.
(7) A gas vent shall terminate at least 3 feet (914 mm) above a forced air inlet located within 10 feet (3048 mm). [NFPA 54:12.7.3]
FIGURE 802.6.1
TERMINATION LOCATIONS FOR
GAS VENTS WITH LISTED CAPS 12 INCHES OR LESS IN
SIZE NOT LESS THAN 8 FEET FROM A VERTICAL WALL
[NFPA 54: FIGURE 12.7.3]
2025 CALIFORNIA MECHANICAL CODE 157
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
CHIMNEYS AND VENTS
TABLE 802.6.1
ROOF SLOPE HEIGHTS
[NFPA 54: TABLE 12.7.3]
California Residential Code High relevance — show source text
IN THOUSANDS OF BTU PER HOUR**|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)|FAN|FAN|NAT|FAN|FAN|NAT|FAN|FAN|NAT| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)|Min|Max|Max|Min|Max|Max|Min|Max|Max| |6|1
2
3|292
301
309|366
432
491|200
231
269|362
373
381|474
557
634|252
299
348|499
509
519|594
696
793|316
376
437| |8|1
2
3|313
323
332|407
465
509|207
238
274|387
397
407|530
607
663|263
309
356|529
540
551|672
766
838|331
391
450| |10|1
2
3|333
343
352|434
489
530|213
244
279|410
420
430|571
640
694|273
317
363|558
569
580|727
813
880|343
403
459| |15|1
2
3|349
359
368|502
548
586|225
256
289|445
456
466|646
706
755|291
334
378|623
634
646|808
884
945|366
424
479| |20|1
2
3|345
355
365|569
610
644|235
266
298|439
450
461|734
787
831|306
348
391|614
627
639|921
986
1042|387
443
496| |30|1
2
3|338
348
358|665
699
729|250
282
312|430
442
452|864
908
946|330
372
412|600
613
626|1089
1145
1193|421
473
524| |50|1
2CRC § 509.2.6.1 High relevance — show source text
509.2.6.1 Through-the-Wall Vent Termination. Through-the-wall vent terminations for listed directvent appliances shall be in accordance with Section 509.8.1. [NFPA 54:12.3.5.2]
509.2.7 Appliances with Integral Vents. Appliances incorporating integral venting means shall be installed in accordance with Section 509.8. [NFPA 54:12.3.6] 509.3 Minimum Safe Performance. Venting systems shall be designed and constructed to convey all flue and vent gases to the outdoors. [NFPA 54:12.1] 509.3.1 Appliance Draft Requirements. A venting system shall satisfy the draft requirements of the appliance in accordance with the manufacturer’s instructions.
[NFPA 54:12.4.1]
509.3.2 Appliance Venting Requirements. Appliances required to be vented shall be connected to a venting system designed and installed in accordance with the provisions of Section 509.4 through Section 509.15.
[NFPA 54:12.4.2] 509.3.3 Mechanical Draft Systems. Mechanical draft systems shall be listed in accordance with UL 378 and installed in accordance with both the appliance and the mechanical draft system manufacturer’s installation instructions. [NFPA 54:12.4.3.1]
2025 CALIFORNIA PLUMBING CODE 91
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
WATER HEATERS
509.3.3.1 Venting. Appliances requiring venting shall be permitted to be vented by means of mechanical draft systems of either forced or induced draft design. [NFPA 54:12.4.3.2]
509.3.3.2 Leakage. Forced draft systems and all portions of induced draft systems under positive pressure during operation shall be designed and installed so as to prevent leakage of flue or vent gases into a building. [NFPA 54:12.4.3.3]
509.3.3.3 Vent Connectors. Vent connectors serving appliances vented by natural draft shall not be connected into any portion of mechanical draft systems operating under positive pressure. [NFPA 54:12.4.3.4]
509.3.3.4 Operation. Where a mechanical draft system is employed, provision shall be made to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance. [NFPA 54:12.4.3.5]
509.3.4 Ventilating Hoods and Exhaust Systems. Where automatically operated appliances, other than food service appliances, are vented through a ventilating hood or exhaust system equipped with a damper or with a power means of exhaust, provisions shall be made to allow the flow of gas to the main burners only when the damper is open to a position to properly vent the appliance and when the power means of exhaust is in operation. [NFPA 54:12.4.4.1]
California Residential Code High relevance — show source text
(inch)|TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch)|TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER –****D (inch)| |||8|8|8|9|9|9|10|10|10| |||APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)|FAN|FAN|NAT|FAN|FAN|NAT|FAN|FAN|NAT| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)**|Min|Max|Max|Min|Max|Max|Min|Max|Max| |6|1
2
3|92
95
97|296
333
363|185
220
248|109
112
114|376
424
463|237
282
317|128
131
134|466
526
575|289
345
386| |8|1
2
3|100
103
105|320
356
384|194
230
258|118
121
123|408
454
492|248
294
330|138
141
143|507
564
612|303
358
402| |10|1
2CRC § 17.44 High relevance — show source text
85| |60|30|7:12|17.44|18.99|22.29|25.85|29.67|33.76|12.54| |60|30|12:12|24.62|26.81|31.46|36.49|41.89|47.66|14.48| |60|45|< 1:12|10.27|11.18|13.12|15.21|17.47|19.87|10.50| |60|45|5:12|14.26|15.52|18.22|21.13|24.26|27.60|12.82| |60|45|7:12|20.21|22.01|25.83|29.95|34.39|39.12|13.86| |60|45|12:12|31.20|33.97|39.87|46.23|53.07|60.39|16.76| |60|60|< 1:12|10.64|11.59|13.60|15.77|18.11|20.60|10.70| |60|60|5:12|14.77|16.09|18.88|21.90|25.14|28.60|13.79| |60|60|7:12|23.05|25.09|29.45|34.15|39.21|44.61|15.18| |60|60|12:12|37.97|41.34|48.52|56.27|64.60|73.49|19.05| |For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 pound force per linear foot = 0.146 kN/m, 1 pound per square foot = 47.88 Pa.
a. Tabulated lengths were derived by calculating design wind pressures in accordance with Figure 28.4-1 of ASCE 7 for a building with a mean roof height of 35 feet, topographic
factor,Kzt, equal to 1.0, and Risk Category II. For wind perpendicular to the ridge, the effects of a 2-foot overhang on each endwall are included. The design pressures were
used to calculate forces to be resisted by solid wall segments in each endwall. The forces to be resisted by each wall line were then divided by the default design strength of
840 pounds per linear foot of length to determine the unreduced length,UR, of solid wall length required in each endwall. The actual mean roof height of the building shall
not exceed the least horizontal dimension of the building.
b. Tabulated lengths in the “minimum” column are based on the requirement of Section 28.4.4 of ASCE 7 that the main windforce-resisting system be designed for a minimum
pressure of 1016 psf multiplied by the wall area of the building and 8 psf multiplied by the roof area of the building projected onto a vertical plane normal to the assumed
wind direction. Tabulated lengths in shaded cells are less than the “minimum” value. Where the minimum controls, it is permitted to be reduced in accordance with Notes c,
d and e. See Section R608.7.1.1.
c.CRC § 509.2.1 High relevance — show source text
** Where any or all of the appliances in Section 509.2.1(1) and Section 509.2.1(2) are installed so the aggregate input rating exceeds 20 (Btu/h)/ft [3] (207 W/m [3] ) of room or space in which it is installed, one or more shall be provided with venting systems or other approved means for conveying the vent gases to the outdoors so that the aggregate input rating of the remaining unvented appliances does not exceed 20 (Btu/h)/ft [3] (207 W/m [3] ). [NFPA 54:12.3.2.1] 509.2.3 Adjacent Room or Space. Where the calculation includes the volume of an adjacent room or space, the room or space in which the appliances are installed shall be directly connected to the adjacent room or space by a doorway, archway, or other opening of comparable size that cannot be closed. [NFPA 54:12.3.2.2]
509.2.4 Ventilating Hoods. The use of ventilating hoods and exhaust systems to vent appliances shall be limited to industrial appliances and appliances installed in commercial applications. [NFPA 54:12.3.3] 509.2.5 Well-Ventilated Spaces. The flue gases from industrial-type appliances shall not be required to be vented to the outdoors where such gases are discharged into a large and well-ventilated industrial space. [NFPA 54:12.3.4]
509.2.6 Direct-Vent Appliances. Listed direct vent appliances shall be installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.3.5.1]
509.2.6.1 Through-the-Wall Vent Termination. Through-the-wall vent terminations for listed directvent appliances shall be in accordance with Section 509.8.1. [NFPA 54:12.3.5.2]
509.2.7 Appliances with Integral Vents. Appliances incorporating integral venting means shall be installed in accordance with Section 509.8. [NFPA 54:12.3.6] 509.3 Minimum Safe Performance. Venting systems shall be designed and constructed to convey all flue and vent gases to the outdoors. [NFPA 54:12.1] 509.3.1 Appliance Draft Requirements. A venting system shall satisfy the draft requirements of the appliance in accordance with the manufacturer’s instructions.
[NFPA 54:12.4.1]
509.3.2 Appliance Venting Requirements. Appliances required to be vented shall be connected to a venting system designed and installed in accordance with the provisions of Section 509.4 through Section 509.15.
[NFPA 54:12.4.2] 509.3.3 Mechanical Draft Systems. Mechanical draft systems shall be listed in accordance with UL 378 and installed in accordance with both the appliance and the mechanical draft system manufacturer’s installation instructions. [NFPA 54:12.4.3.1]
2025 CALIFORNIA PLUMBING CODE 91
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
WATER HEATERS
California Residential Code High relevance — show source text
METAL VENT CONNECTOR DIAMETER –D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)| |||8|8|8|9|9|9|10|10|10| |||APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)|FAN|FAN|NAT|FAN|FAN|NAT|FAN|FAN|NAT| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)**|Min|Max|Max|Min|Max|Max|Min|Max|Max| |6|1
2
3|292
301
309|366
432
491|200
231
269|362
373
381|474
557
634|252
299
348|499
509
519|594
696
793|316
376
437| |8|1
2
3|313
323
332|407
465
509|207
238
274|387
397
407|530
607
663|263
309
356|529
540
551|672
766
838|331
391
450| |10|1
2CRC § 12.7.2 High relevance — show source text
(4) Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.
[NFPA 54:12.7.2]
509.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements:
(1) A gas vent shall terminate in accordance with one of the following:
(a) Gas vents that are 12 inches (300 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall
terminate above the roof in accordance with Figure 509.6.1 and Table 509.6.1.
(b) Gas vents that are over 12 inches (300 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above any portion of a building within 10 feet (3048 mm) horizontally.
(c) Industrial appliances as provided in Section 509.2.5.
(d) Direct-vent systems as provided in Section 509.2.6.
(e) Appliances with integral vents as provided in Section 509.2.7.
(f) Mechanical draft systems as provided in Section 509.3.3 through Section 509.3.3.4.
(g) Ventilating hoods and exhaust systems as provided in Section 509.3.4.
(2) A Type B or a Type L gas vent shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar.
(3) A Type B-W gas vent shall terminate at least 12 feet (3658 mm) in vertical height above the bottom of the wall furnace.
(4) A gas vent extending through an exterior wall shall not terminate adjacent to the wall or below eaves or parapets, except as provided in Section 509.2.6 and Section 509.3.3 through Section 509.3.3.4.
(5) Decorative shrouds shall not be installed at the termination of gas vents except where such shrouds are listed for use with the specific gas venting system and are installed in accordance with the manufac turer’s installation instructions.
(6) All gas vents shall extend through the roof flashing, roof jack, or roof thimble and terminate with a listed cap or listed roof assembly.
(7) A gas vent shall terminate at least 3 feet (914 mm) above a forced air inlet located within 10 feet (3048 mm). [NFPA 54:12.7.3]
FIGURE 509.6.1
TERMINATION LOCATIONS FOR GAS
VENTS WITH LISTED CAPS 12 INCHES OR LESS IN SIZE
AT LEAST 8 FEET FROM A VERTICAL WALL
[NFPA 54: FIGURE 12.7.3]
TABLE 509.6.1
ROOF SLOPE HEIGHTS
[NFPA 54: TABLE 12.7.3]
CRC § 12.8.4.6 High relevance — show source text
(1829 mm) of metal pipe in the opening between the draft hood outlet and the thimble, the thimble shall be a minimum of 2 inches (51 mm) larger in diameter than the metal pipe.
(2) For unlisted appliances having draft hoods, the thimble shall be a minimum of 6 inches (152 mm) larger in diameter than the metal pipe.
(3) For residential and low-heat appliances, the thimble shall be a minimum of 12 inches (305 mm) larger in diameter than the metal pipe.
Exception: In lieu of thimble protection, all combustible material in the wall shall be removed a suffi cient distance from the metal pipe to provide the
«
«
2025 CALIFORNIA MECHANICAL CODE 159
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
CHIMNEYS AND VENTS
specified clearance from such metal pipe to combustible material. Any material used to close up such opening shall be noncombustible. [NFPA 54:12.8.4.6] 802.7.4 Size of Single-Wall Metal Pipe. Single-wall metal piping shall comply with the following require ments:
(1) A venting system of a single-wall metal pipe shall be sized in accordance with one of the following methods and the appliance manufacturer’s instructions:
(a) For a draft hood-equipped appliance, in accordance with Section 803.0.
(b) For a venting system for a single appliance with a draft hood, the areas of the connector and the pipe each shall not be less than the area of the appliance flue collar or draft hood outlet, whichever is smaller. The vent area shall not be greater than seven times the draft hood outlet area.
(c) Engineering methods.
(2) Where a single-wall metal pipe is used and has a shape other than round, it shall have an equivalent effective area equal to the effective area of the round pipe for which it is substituted and the minimum internal dimension of the pipe shall be 2 inches (51 mm).
(3) The vent cap or a roof assembly shall have a venting capacity not less than that of the pipe to which it is attached. [NFPA 54:12.8.5]
802.7.5 Support of Single-Wall Metal Pipe. All portions of single-wall metal pipe shall be supported for the design and weight of the material employed. [NFPA 54:12.8.6]
802.7.6 Marking. Single-wall metal pipe shall comply with the marking provisions of Section 802.6.5. [NFPA 54:12.8.7]
802.8 Through-the-Wall Vent Termination. Throughthe-wall vent termination shall be in accordance with Section
802.8.1 through Section 802.8.3.
802.8.1 Clearance for Through-the-Wall Vent Ter- mination. The clearance for through-the-wall direct vent and non-direct vent terminals shall be in accordance with
Table 802.8.1 and Figure 802.8.1.
Exception: The clearances in Table 802.8.1 shall not apply to the combustion air intake of a direct vent appliance. [NFPA 54:12.9.1]
CRC § 25.4 High relevance — show source text
For intermediate values of sidewall length, endwall length, roof slope and basic wind speed, use the next higher value, or determine by interpolation.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 pound force per linear foot = 0.146 kN/m, 1 pound per square foot = 47.88 Pa.
a. Tabulated lengths were derived by calculating design wind pressures in accordance with Figure 28.4-1 of ASCE 7 for a building with a mean roof height of 35 feet, topographic
factor,Kzt, equal to 1.0, and Risk Category II. For wind perpendicular to the ridge, the effects of a 2-foot overhang on each endwall are included. The design pressures were
used to calculate forces to be resisted by solid wall segments in each endwall. The forces to be resisted by each wall line were then divided by the default design strength of
840 pounds per linear foot of length to determine the unreduced length,UR, of solid wall length required in each endwall. The actual mean roof height of the building shall
not exceed the least horizontal dimension of the building.
b. Tabulated lengths in the “minimum” column are based on the requirement of Section 28.4.4 of ASCE 7 that the main windforce-resisting system be designed for a minimum
pressure of 1016 psf multiplied by the wall area of the building and 8 psf multiplied by the roof area of the building projected onto a vertical plane normal to the assumed
wind direction. Tabulated lengths in shaded cells are less than the “minimum” value. Where the minimum controls, it is permitted to be reduced in accordance with Notes c,
d and e. See Section R608.7.1.1.
c. For buildings with a mean roof height of less than 35 feet, tabulated lengths are permitted to be reduced by multiplying by the appropriate factor,_R_1, from Table R608.7.1.1(4).
The reduced length shall be not less than the “minimum” value shown in the table.
d. Tabulated lengths for “one story or top story of two story” are based on a floor-to-ceiling height of 10 feet. Tabulated lengths for “first story of two story” are based on floor-
to-ceiling heights of 10 feet each for the first and second story. For floor-to-ceiling heights less than assumed, use the lengths in this table or Table R608.7.1.1(1) or
R608.7.1.1(3), or multiply the value in the table by the reduction factor,_R_2, from Table R608.7.1.1(5).
e. Tabulated lengths are based on the default design shear strength of 840 pounds per linear foot of solid wall segment. The tabulated lengths are permitted to be reduced by
multiplying by the applicable reduction factor for design strength,_R_3, from Table R608.7.1.1(6).
f. The reduction factors,_R_1, _R_2 and_R_3, in Tables R608.7.1.1(4), R608.7.1.1(5), and R608.7.1.1(6), respectively, are permitted to be compounded, subject to the limitations of Note
b.CRC § 509.7.3.4 Medium relevance — show source text
Clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . .509.7.3.4,
Table 509.7.3.4(1), Table 509.7.3.4(2)
Dampers . . . . . . . . . . . . . . . . . . . . . . . .509.13, 509.14,
509.14.1
Direct-vent . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509.2.6
General requirements . . . . . . . . . . . . . . . . . . . . . .509.0
Insulation shield . . . . . . . . . . . . . . . . . . . . . . . .509.6.1.1
Integral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509.2.7 Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509.1
Mechanical draft . . . . . . . . . . . . . . . .509.3.3, 509.3.3.4
Obstruction of flow . . . . . . . . . . . . . . . . . . . . . . . .509.15
Plastic piping . . . . . . . . . . . . . . . . . . . . . . . . . . .509.4.1 Special . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509.4.3
568 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
INDEX
Termination . . . . . . . . . . . . . . . .509.6.1, 509.7.2, 509.8
Wall penetrations . . . . . . . . . . . . . . . . . . . . . . . . . .509.8 FUEL GAS VENT, SIZING Category I appliances . . . . . . . . . . . . . .509.6.2.1, 510.0 Multiple appliances . . . . . . . . . . . . . . . . . . . . . . . .510.2, Table 510.2(1) – Table 510.2(9) Multistory . . . . . . . . . . . . . . . . . . . . .509.6.3, 509.6.3.2,
510.2.13 – 510.2.16
Single appliance . . . . . . . . . . .509.7.4(1)(b), 509.10.2.1,
510.1, 510.1.2,
Table 510.1.2(1) – Table 510.1.2(6)
FUTURE CONNECTIONS . . . . . . . . . . . . . . . . . . . .1504.9.1
– G –
Frequently asked questions
What does “listed” mean for a mechanical draft system?
“Listed” means the mechanical draft system has been tested and labeled by a recognized testing laboratory to the standard specified by the code — in this case UL 378 for mechanical draft systems — and must be installed per the manufacturer’s instructions (§ 509.3.3) .
Can I tie a natural‑draft water heater into an existing fan‑assisted vent?
No — the code explicitly forbids connecting vent connectors serving natural‑draft appliances into any portion of a mechanical draft system that operates under positive pressure (§ 509.3.3.3) .
If my direct‑vent appliance is listed, do I still need to follow code termination tables?
Yes — § 509.2.6 requires installation per the manufacturer’s instructions and points to the through‑wall termination provisions (e.g., § 509.8.1) for through‑the‑wall terminations; you must satisfy both the listing/manufacturer instructions and the applicable code termination/clearance rules .
What must I do if a mechanical draft fan fails?
The code requires a provision to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy appliance safe‑operation requirements (an interlock, switch, or similar) (§ 509.3.3.4) .
Are there any numeric vent clearances in §§ 509.2.6, 509.2.7 or 509.3.3?
No — those sections defer to the appliance manufacturer’s instructions and to other code sections (for example § 509.8.1 for through‑the‑wall terminations). For numeric clearances and termination heights consult the referenced sections in the code (e.g., § 509.8.1, § 509.6.1) .
More in California Residential Code
Ask about the CRC
Get cited, plain-English answers on the California Residential Code for your project — any code section, any scenario.
Start Free Trial