CPC · California Plumbing Code

Vent types, vent sizing, and maximum lengths/unit loading for vents

Q: What is the minimum vent diameter I can use?

Minimum vent diameter is 1 1/4 inches ; an individual vent must also be at least one-half the diameter of the drain it serves. See § 703.2 and Appendix C for details.

Q: How much of a vent can be horizontal?

No more than one-third of the permitted developed length of a vent may be installed in a horizontal position (Table 703.2 note). § 703.2 .

Q: When do I have to increase vent size for length?

If a branch vent’s developed length exceeds 40 ft , Appendix C requires increasing the vent one pipe size for the entire developed length. § C 401.3 .

Q: Do the Table 703.2 length limits always apply?

If the vent is increased by one pipe size for its entire length , the table’s maximum length limits do not apply (Table 703.2 note). § 703.2 .

Q: Where do I get fixture-unit values?

Use Table 702.1 (Drainage Fixture Unit values) and Table 702.2 for intermittent/continuous flows to compute DFU before using Table 703.2. § 702.1 .

For homeowners: the California Plumbing Code requires vents be sized by the number of fixture units and the vent’s length — consult Table 703.2 to pick a vent size that handles your total fixture-load and is not longer than the table’s maximum developed length, observe a minimum 1 1/4" vent diameter and that only up to one-third of the vent may be horizontal; Appendix C requires upsizing when branch vents exceed 40 ft.

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Last reviewed: July 6, 2026

What the code requires — plain English

The California Plumbing Code requires vents to be sized for the number of connected fixture units and the vent’s developed length. The controlling table for maximum fixture-unit loads and maximum lengths of both drainage and vent piping is Table 703.2 (see § 703.2) and vent-installation principles are found in Chapter 9 (Vents) of the CPC. See § 703.2 and Chapter 9 for the primary sizing/length limits and the rules that protect trap seals and allow exceptions.

Most important: size the vent by adding the fixture-unit load that will discharge into it and then check Table 703.2 (vent piping row) for the permitted maximum fixture units and the maximum developed length; also observe minimum diameters and horizontal limits called out in the table notes.

Requirements in detail

Key defined terms (first mention bolded)

Vent — a pipe that admits air to and from the drainage system to prevent trap siphonage and relieve pressure (see Chapter 9).
Fixture unit (DFU) — the sizing unit used to compute load on drains and vents (see Table 702.1).
Developed length — the measured length of vent piping (vertical + allowed horizontal portions) used for sizing (see Appendix C guidance).

Table — Vent piping: common decision values

This condensed table extracts the decision-relevant vent values from Table 703.2 (vent piping row). Always use the full table in § 703.2 for final design.

Vent size (in)	Maximum fixture units (vent piping)	Maximum developed length (feet)	Code reference
1 1/4	1	45 ft	§ 703.2
1 1/2	8	60 ft	§ 703.2
2	24	120 ft	§ 703.2
3	84	212 ft	§ 703.2
4	256	300 ft	§ 703.2
5	600	390 ft	§ 703.2
6	1,380	510 ft	§ 703.2
8	3,600	750 ft	§ 703.2

Notes from the table and related code (decision rules):

Minimum vent diameter is 1 1/4 in. and an individual vent must be not less than one-half the diameter of the drain it serves — see table notes and Appendix C sizing guidance.
Not more than one-third of the permitted developed length of a vent may be installed horizontally (table note).
Where a branch vent’s developed length exceeds 40 ft, Appendix C requires the vent be increased one pipe size for the entire developed length. See § C 401.3 / § C 401.1.

Sizing process — step-by-step (code-grounded)

Compute total fixture-unit load using Table 702.1 / Table 702.2 (DFU values).
Select a vent pipe size whose Maximum Units (vent piping row of Table 703.2) ≥ your total DFU. § 703.2.
Verify the vent’s developed length does not exceed the Maximum Length shown in Table 703.2 for that size. § 703.2.
Confirm the horizontal portion is ≤ one-third of the permitted length (table note). § 703.2.
Apply Appendix C rules where applicable (e.g., increase size when branch vents > 40 ft developed length). § C 401.3 / § C 401.1.

Exceptions & special cases

Vents increased one pipe size for their entire length: when a vent is upsized by one size for its entire developed length, the maximum length limits in Table 703.2 do not apply (Table 703.2 note). § 703.2.
Minimum size constraints: vents may not be smaller than 1 1/4 in. and must be at least one-half the diameter of the drain they serve (table note / Appendix C). § 703.2; § C 401.1.
Long branch or branch-vent runs: Appendix C requires upsizing one pipe size where branch vents exceed 40 ft developed length. § C 401.3.
Circuit vents / relief vents / engineered vents: special vent arrangements (circuit vents, relief vents, engineered vent systems) have their own sizing/connection rules in Chapter 9 and Sections 911 and 912. See § 911.2.1, § 911.3, and § 912.1 for these special cases.

If a required item above (for example a specific Appendix C table entry) is not present in the provided files, state it plainly instead of inventing values. (In this article, the CPC excerpts needed for the items listed are present in the files cited.)

Common mistakes (and how to avoid them)

Mistake: using the “vertical” fixture-unit column when you should use the vent piping row. Fix: always read the vent piping row of Table 703.2 for vent sizing. § 703.2.
Mistake: forgetting the one-third horizontal limit and routing too much vent horizontally. Fix: ensure horizontal portion ≤ one-third of permitted developed length per Table 703.2 note. § 703.2.
Mistake: selecting a vent smaller than 1 1/4 in. or smaller than one-half the connected drain. Fix: observe minimum diameter rules in Table 703.2 and Appendix C. § 703.2; § C 401.1.
Mistake: failing to upsize vents when branch vents exceed 40 ft developed length. Fix: apply Appendix C requirement to increase one pipe size. § C 401.3.

Worked example — apply the rule with numbers

Scenario: a branch will discharge a total of 70 DFU to a single vent. The developed length from the lowest fixture connection to termination outdoors is 150 ft, and the horizontal portion will be 30 ft.

From Table 703.2 (vent piping) find a vent size that can carry ≥70 DFU: a 3 in. vent is rated for 84 DFU and a maximum length of 212 ft. § 703.2.
Check developed length: 150 ft < 212 ft → OK for the 3 in. vent. § 703.2.
Check horizontal limit: Table note allows up to one-third of permitted length horizontally. One-third of 212 ft = 70.7 ft; actual horizontal portion is 30 ft, which is less → OK. § 703.2.
Minimum diameter check: 3 in. > 1 1/4 in. and greater than one-half the drain diameter (confirm drain diameter separately) → OK. § 703.2; § C 401.1.

Conclusion: a 3 in. vent is code-compliant for this scenario per § 703.2 and Chapter 9 guidance, so long as other Chapter 9 installation rules (distance from traps, connections, etc.) are observed.

Related provisions (quick list)

§ 703.2 — Table 703.2, Maximum unit loading and maximum lengths (vent piping row).
Chapter 9 (Vents) — general venting principles, materials, trap protection and installation rules.
§ C 401.1 and § C 401.3 — Appendix C alternate vent sizing rules and the requirement to increase branch vent one size when developed length > 40 ft.
Table 702.1 / § 702.1 — drainage fixture unit values (use these to compute DFU).
§ 911.2.1 / § 911.3 — circuit venting and relief vent requirements (special vent arrangements).

If you want, I can:

Pull the full text of Table 703.2 (verbatim table image/text) for use on plans, or
Run through your plan’s fixture list and produce the exact vent size/length checks step-by-step citing the CPC entries used.

Code references

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

CPC § 510.2.1 High relevance — show source text
Therefore, a 3 inch (76 mm) single-wall metal vent connector can be used with the water heater. For a draft hood-equipped furnace with a 3 foot (914 mm) rise, read across the appropriate row to find that a 5 inch (127 mm) diameter vent connector has a maximum capacity of 120 000 Btu/h (35 kW) (which is too small for the furnace) and a 6 inch (152 mm) diameter vent connector has a maximum vent capacity of 172 000 Btu/h (50 kW). Therefore, a 6 inch (152 mm) diameter vent connector should be used with the 150 000 Btu/h (44 kW) furnace. Because both vent connector, horizontal lengths are less than the maximum lengths listed in Section 510.2.1; the table values can be used without adjustments.

In the common vent capacity portion of Table 510.2(2), find the row associated with a 30 foot (9144 mm) vent height and read over to the NAT + NAT portion of the 6 inch (152 mm) diameter column to find a maximum combined capacity of 257 000 Btu/h (75 kW). Since the two appliances total only 185 000 Btu/h (54 kW), a 6 inch (152 mm) common vent can be used. [NFPA 54:F.2.1]

For SI units: 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW

FIGURE G 101.6

COMMON VENTING TWO DRAFT HOOD-EQUIPPED

APPLIANCES – EXAMPLE 4

[NFPA 54: FIGURE F.2.1]

G 101.7 Example 5(a): Common Venting a Draft Hood-Equipped Water Heater with a Fan-Assisted Furnace into a Type B Vent. In this case, a 35 000 Btu/h (10.3 kW) input draft hood-equipped water heater with a 4 inch (102 mm) diameter draft hood outlet, 2 feet (610 mm) of connector rise, and 4 feet (1219 mm) of horizontal length is to be common vented with a 100 000 Btu/h (29 kW) fanassisted furnace with a 4 inch (102 mm) diameter flue collar, 3 feet (914 mm) of connector rise, and 6 feet (1829 mm) of horizontal length. The common vent consists of a 30 foot (9144 mm) height of Type B vent. What are the recommended vent diameters for each connector and the common vent? The installer would like to use a single-wall metal vent connector. (See Figure G 101.7)

Solution:

Water Heater Vent Connector Diameter. Since the water heater vent connector, horizontal length of 4 feet (1219 mm) is less than the maximum value listed in Table 510.2(2), the venting table values can be used without adjustments. Using the Vent Connector Capacity portion of Table 510.2(2), read down the Total Vent Height ( H ) column to 30 feet (9144 mm) and read across the 2 feet (610 mm) Connector Rise ( R ) row to the first Btu/h rating in the NAT Max column that is equal to or greater than the water heater input rating. The table shows that a 3 inch (76 mm) vent connector has a maximum input rating of 37 000 Btu/h (10.8 kW).
CPC § 509.6.1 High relevance — show source text
A Type B vent or listed chimney lining system passing through an unused masonry chimney flue shall not be considered to be exposed to the outdoors. Where vents extend outdoors above the roof more than 5 feet (1524 mm) higher than required by Table 509.6.1, and where vents terminate in accordance with Section 509.6.1(1)(b), the outdoor portion of the vent shall be enclosed as required by this paragraph for vents not considered to be exposed to the outdoors, or such venting system shall be engineered. A Type B vent passing through an unventilated enclosure or chase insulated to a value of not less than R-8 shall not be considered to be exposed to the outdoors. Table 510.1.2(3) in combination with Table 510.1.2(6) shall be used for claytilelined exterior masonry chimneys, provided all of the following requirements are met:

(1) The vent connector is Type B double wall.

(2) The vent connector length is limited to 18 inches per inch (18 mm/mm) of vent connector diameter.

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WATER HEATERS

(3) The appliance is draft hood equipped.

(4) The input rating is less than the maximum capacity given in Table 510.1.2(3).

(5) For a water heater, the outdoor design temperature shall not be less than 5°F (-15°C).

(6) For a space-heating appliance, the input rating is greater than the minimum capacity given by Table 510.1.2(6). [NFPA 54:13.1.11] 510.1.11 Corrugated Vent Connector Size. Corrugated vent connectors shall not be smaller than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. [NFPA 54:13.1.12]

510.1.12 Upsizing. Vent connectors shall not be upsized more than two sizes greater than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. [NFPA 54:13.1.13]

510.1.13 Multiple Vertical Vent Sizes. In a single run of vent or vent connector, more than one diameter and type shall be permitted to be used, provided that all the sizes and types are permitted by the tables. [NFPA 54:13.1.14]

510.1.14 Interpolation. Interpolation shall be permitted in calculating capacities for vent dimensions that fall between table entries. [NFPA 54:13.1.15]

510.1.15 Extrapolation. Extrapolation beyond the table entries shall not be permitted. [NFPA 54:13.1.16] 510.1.16 Sizing Vents Not Covered by Tables. Where a vent height is lower than 6 feet (1829 mm) or higher than shown in Table 510.1.2(1) through Table 510.2(9), an engineering method shall be used to calculate the vent capacity. [NFPA 54:13.1.17]
CPC § 911.2.1 High relevance — show source text
waste.

911.2.1 Multiple Circuit Vents. When multiple circuit vents are interconnected according to Section 911.4.1, each individual circuit vent shall be sized according to Section 911.2. The vent pipe connecting each circuit vent shall be sized according to Table 703.2.

911.3 Relief Vent. A 2 inch (50 mm) relief vent shall be provided for circuit-vented horizontal branches receiving the discharge of four or more water closets when connecting to a drainage stack that receives the discharge of soil or waste from upper horizontal branches.

911.3.1 Connection and Installation. The relief vent

shall connect to the horizontal branch between the stack and the most downstream trap arm of the circuit vent. The relief vent shall be installed on the vertical to the

horizontal branch.

911.3.2 Fixture Drain. The relief vent is permitted to serve as a fixture drain. Fixtures discharging to a relief vent shall be one or two fixture unit fixtures but shall not

exceed a total of 4 fixture units.

911.4 Slope and Size of Horizontal Branch. The vented section of the horizontal branch shall be uniformly sloped and not more than 1 inch per foot (83.3 mm/m). The entire length of the vented section of the horizontal branch shall be sized for the total drainage discharge to the branch according to Table 703.2.

911.4.1 Multiple Circuit-Vented Branches. Circuitvented horizontal branches are permitted to be connected together. Each group of a maximum of eight fixtures shall be considered a separate circuit vent and shall be in accordance with Section 911.4.1.1 and Section 911.4.1.2.

911.4.1.1 Size of Parallel Horizontal

Branches. Parallel horizontal circuit vented branches shall be permitted to connect on the same floor level. Each separate circuit-vented horizontal branch that is interconnected shall be sized independently in accordance with Section 911.4.

911.4.1.2 Size of Continuous Horizontal Branches. Two or more circuit vented systems continuous on the same horizontal branch shall be uniformly sized for the total discharge into the branch.

911.5 Additional Fixtures. Fixtures, other than the circuitvented fixtures, are permitted to discharge to the horizontal branch drain. Such fixtures shall be located on the same floor as the circuit-vented fixtures and shall be either individually or common vented.

912.0 Engineered Vent System. 912.1 General. The design and sizing of a vent system shall be permitted to be determined by accepted engineering practices. The system shall be designed by a registered design professional and approved in accordance with Section 301.5. 912.2 Minimum Requirements. An engineered vent system shall provide protection of the trap seal in accordance with Section 901.3.

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CALIFORNIA PLUMBING CODE – MATRIX ADOPTION TABLE

CHAPTER 10 - TRAPS AND INTERCEPTORS

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
CPC § 25.4 High relevance — show source text
For SI Units: 1 inch = 25.4 mm, 1 foot = 304.8 mm

509.6.1.1 Insulation Protection Shield. Where a vent passes through an insulated assembly, an approved metal shield constructed of steel having a thickness of not less than 26 gauge (0.0179 inch) (0.45 mm) (No. 26 gauge) shall be installed between the vent and insulation. The shield shall extend not less than 2 inches (51 mm) above the insulation and be secured to the structure in accordance with the

manufacturer’s installation instructions.

509.6.2 Size of Gas Vents. Venting systems shall be sized and constructed in accordance with Section

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WATER HEATERS

509.6.2.1 through Section 509.6.2.3 and the appliance manufacturer’s instructions. [NFPA 54:12.7.4] 509.6.2.1 Category I Appliances. The sizing of natural draft venting systems serving one or more listed appliances equipped with a draft hood or appliances listed for use with a Type B gas vent, installed in a single story of a building, shall be in accordance with one of the following:

(1) The provisions of Section 510.0.

(2) Vents serving fan-assisted combustion system appliances, or combinations of fan-assisted combustion system and draft hood-equipped appliances, shall be sized in accordance with Section 510.0 or other engineering methods.

(3) For sizing an individual gas vent for a single, draft hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet or greater than seven times the draft hood outlet area.

(4) For sizing a gas vent connected to two appliances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.

(5) Engineering methods. [NFPA 54:12.7.4.1] 509.6.2.2 Vent Offsets. Type B and Type L vents sized in accordance with Section 509.6.2.1(3) or Section 509.6.2.1(4) shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60 degree (1.05 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.4.2] 509.6.2.3 Category II, Category III, and Cate- gory IV Appliances. The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturers’ instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, III, and IV appliances shall be in accordance with the appliance manufacturers’ instructions.
CPC § 702.2 High relevance — show source text
Table 702.2 Discharge Capacity in Gallons Per Minute for

Intermittent Flow Only . . . . . . . . .168

702.3 Continuous Flow . . . . . . . . . . . . . .168

703.0 Size of Drainage Piping . . . . . . . .168

703.1 Minimum Size . . . . . . . . . . . . . . . .168

703.2 Maximum Number of Fixture

Units . . . . . . . . . . . . . . . . . . . . . . .168

703.3 Sizing per Appendix C . . . . . . . . .168

704.0 Fixture Connections (Drainage) . .168

704.1 Inlet Fittings . . . . . . . . . . . . . . . . .168

704.2 Single Vertical Drainage Pipe . . . .168

704.3 Commercial Sinks . . . . . . . . . . . . .168

Table 703.2 Maximum Unit Loading and Maximum Length of Drainage and Vent Piping . . . . . . . . . . . . . .169

705.0 Joints and Connections . . . . . . . .169

705.1 ABS and ABS Co-Extruded

Plastic Pipe and Joints . . . . . . . . .169

705.2 Cast-Iron Pipe and Joints . . . . . . .169

705.3 Copper or Copper Alloy Pipe (DWV) and Joints . . . . . . . . .170

705.4 Galvanized Steel Pipe and Joints . . . . . . . . . . . . . . . . . . .170

705.5 Polyethylene (PE) Sewer Pipe . . .170

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TABLE OF CONTENTS

705.6 PVC and PVC Co-Extruded

Plastic Pipe and Joining Methods . . . . . . . . . . . . . . . . . . . .171

705.7 Stainless Steel Pipe and Joints . . .171

705.8 Vitrified Clay Pipe and Joints . . . .171

705.9 Special Joints . . . . . . . . . . . . . . . .171

705.10 Joints Between

Various Materials . . . . . . . . . . . . .171

706.0 Changes in Direction of Drainage Flow . . . . . . . . . . . . . . .172

706.1 Approved Fittings . . . . . . . . . . . . .172

706.2 Horizontal to Vertical . . . . . . . . . .172

706.3 Horizontal to Horizontal . . . . . . . .172

706.4 Vertical to Horizontal . . . . . . . . . .172

707.0 Cleanouts . . . . . . . . . . . . . . . . . . .172

707.1 Plug . . . . . . . . . . . . . . . . . . . . . . .172

Table 707.1 Cleanouts . . . . . . . . . . . . . . . . . . .172

707.2 Approved . . . . . . . . . . . . . . . . . . .172

CPC § 13.2.2 High relevance — show source text

[NFPA 54: TABLE 13.2.2]

CONNECTOR DIAMETER (inches)	MAXIMUM CONNECTOR HORIZONTAL LENGTH (feet)
3	41⁄2
4	6
5	71⁄2
6	9
7	101⁄2
8	12
9	131⁄2
10	15
12	18
14	21
16	24
18	27
20	30
22	33
24	36

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm

803.2.2 Vent Connector Exceeding Maximum Length. The vent connector shall be routed to the vent utilizing the shortest possible route. Connectors with longer horizontal lengths than those listed in Table 803.2.1 are permitted under the following conditions:

(1) The maximum capacity (FAN Max or NAT Max) of the vent connector shall be reduced 10 percent for each additional multiple of the length listed in Table 803.2.1. For example, the maximum length listed for a 4 inch (100 mm) connector is 6 feet (1829 mm). With a connector length greater than 6 feet (1829 mm) but not exceeding 12 feet (3658 mm), the maximum capacity must be reduced by 10 percent (0.90

TABLE 803.2.1

VENT CONNECTOR MAXIMUM LENGTH

[NFPA 54: TABLE 13.2.2]

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm

2025 CALIFORNIA MECHANICAL CODE 167

CHIMNEYS AND VENTS

maximum common vent capacity listed in the venting tables shall be reduced by 5 percent. For each elbow greater than 45 degrees (0.79 rad) up to and including 90 degrees (1.57 rad), the maximum common vent capacity listed in the venting tables shall be reduced by 10 percent. [NFPA 54:13.2.6]

803.2.6 Elbows in Connectors. The vent connector capacities listed in the common vent sizing tables include allowance for two 90 degree elbows. For each additional elbow up to and including 45 degrees, the maximum vent connector capacity listed in the venting tables shall be reduced by 5 percent. For each elbow greater than 45 degrees up to and including 90 degrees, the maximum vent connector capacity listed in the venting tables shall be reduced by 10 percent. [NFPA 54:13.2.7]

803.2.7 Common Vent Minimum Size. The crosssectional area of the common vent shall be equal to or greater than the cross-sectional area of the largest connector. [NFPA 54:13.2.8]

CPC § 304.8 High relevance — show source text
(feet)
Horizontal (unlimited)|

45|

65|

85|

212|

300|

390|

510|

750|

–|

–| |Vent Piping
Horizontal and Vertical6
Maximum Units
Maximum Lengths, (feet)|

1
45|

83
60|

24
120|

84
212|

256
300|

600
390|

1380
510|

3600
750|

–|

–|

For SI units: 1 inch = 25 mm, 1 foot = 304.8 mm

Notes: 1 Excluding trap arm. 2 Except for sinks, urinals, and dishwashers – exceeding 1 fixture unit. 3 Except for six-unit traps or water closets. 4 Not to exceed six water closets or five six-unit traps. 5 Based on 1 ⁄ 4 inch per foot (20.8 mm/m) slope. For 1 ⁄ 8 of an inch per foot (10.4 mm/m) slope, multiply horizontal fixture units by a factor of 0.8. 6 The diameter of an individual vent shall be not less than 1 1 ⁄ 4 inches (32 mm) nor less than one-half the diameter of the drain to which it is connected. Fixture unit load values for drainage and vent piping shall be computed from Table 702.1 and Table 702.2. Not to exceed one-third of the total permitted length of a vent shall be permitted to be installed in a horizontal position. Where vents are increased one pipe size for their entire length, the maximum length limitations specified in this table do not apply. This table is in accordance with the requirements of Section 901.3. 7 Up to 8 public lavatories are permitted to be installed on a 1 1 ⁄ 2 inch (40 mm) vertical branch or horizontal sanitary branch sloped at 1 ⁄ 4 inch per foot (20.8 mm/m).

line shall be connected between the floor drain waste con nection and the fixture drain. The fixture and floor drain shall be trapped and vented in accordance with this code.

705.0 Joints and Connections.

705.1 ABS and ABS Co-Extruded Plastic Pipe and Joints. Joining methods for ABS plastic pipe and fittings shall be installed in accordance with the manufacturer’s installation instructions and shall comply with Section 705.1.1 through Section 705.1.3. 705.1.1 Mechanical Joints. Mechanical joints shall be designed to provide a permanent seal and shall be of the mechanical or push-on joint. The push-on joint shall include an elastomeric gasket that complies with ASTM D3212 and shall provide a compressive force against the spigot and socket after assembly to provide a permanent seal.
CPC § 510.1.2 High relevance — show source text
(6) For a space-heating appliance, the input rating is greater than the minimum capacity given by Table 510.1.2(6). [NFPA 54:13.1.11] 510.1.11 Corrugated Vent Connector Size. Corrugated vent connectors shall not be smaller than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. [NFPA 54:13.1.12]

510.1.12 Upsizing. Vent connectors shall not be upsized more than two sizes greater than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. [NFPA 54:13.1.13]

510.1.13 Multiple Vertical Vent Sizes. In a single run of vent or vent connector, more than one diameter and type shall be permitted to be used, provided that all the sizes and types are permitted by the tables. [NFPA 54:13.1.14]

510.1.14 Interpolation. Interpolation shall be permitted in calculating capacities for vent dimensions that fall between table entries. [NFPA 54:13.1.15]

510.1.15 Extrapolation. Extrapolation beyond the table entries shall not be permitted. [NFPA 54:13.1.16] 510.1.16 Sizing Vents Not Covered by Tables. Where a vent height is lower than 6 feet (1829 mm) or higher than shown in Table 510.1.2(1) through Table 510.2(9), an engineering method shall be used to calculate the vent capacity. [NFPA 54:13.1.17]

510.1.17 Height Entries. Where the actual height of a vent falls between entries in the height column of the applicable table in Table 510.1.2(1) through Table 510.1.2(6), either of the following shall be used:

(1) Interpolation.

(2) The lower appliance input rating shown in the table entries for FAN Max and NAT Max column values; and the higher appliance input rating for the FAN Min column values. [NFPA 54:13.1.18]

510.2 Additional Requirements to Multiple-Appliance Vent. Venting Table 510.2(1) through Table 510.2(9) shall not be used where obstructions are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer’s instructions, or in accordance with the following:

(1) The maximum capacity of the vent connector shall be determined using the NAT Max column.

(2) The maximum capacity of the vertical vent or chimney shall be determined using the FAN + NAT column when the second appliance is a fan-assisted appliance, or the NAT + NAT column when the second appliance is equipped with a draft hood.

(3) The minimum capacity shall be determined as if the appliance were a fan-assisted appliance, as follows:

(a) The minimum capacity of the vent connector shall be determined using the FAN Min column.
CPC § 701.0 Medium relevance — show source text
701.0 General . . . . . . . . . . . . . . . . . . . . .165

701.1 Applicability . . . . . . . . . . . . . . . . . .165

701.2 Drainage Piping . . . . . . . . . . . . . .165

701.3 Drainage Fittings . . . . . . . . . . . . .165

701.4 Continuous Wastes . . . . . . . . . . .165

701.5 Lead . . . . . . . . . . . . . . . . . . . . . . .165

701.6 Caulking Ferrules . . . . . . . . . . . . .165

701.7 Soldering Bushings . . . . . . . . . . . .165

Table 701.6 Caulking Ferrules . . . . . . . . . . . . .165

Table 701.7 Soldering Bushings . . . . . . . . . . . .165

702.0 Fixture Unit Equivalents . . . . . . . .165

702.1 Trap Size . . . . . . . . . . . . . . . . . . .165

Table 701.2 Materials for Drain, Waste, Vent Pipe and Fittings . . . . . . . . .166

Table 702.1 Drainage Fixture Unit Values (DFU) . . . . . . . . . . . . . . . .167

Table 702.1(1) Maximum Drainage Fixture Units for a Trap and Trap Arm . . .168

702.2 Intermittent Flow . . . . . . . . . . . . . .168

Table 702.2 Discharge Capacity in Gallons Per Minute for

Intermittent Flow Only . . . . . . . . .168

702.3 Continuous Flow . . . . . . . . . . . . . .168

703.0 Size of Drainage Piping . . . . . . . .168

703.1 Minimum Size . . . . . . . . . . . . . . . .168

703.2 Maximum Number of Fixture

Units . . . . . . . . . . . . . . . . . . . . . . .168

703.3 Sizing per Appendix C . . . . . . . . .168

704.0 Fixture Connections (Drainage) . .168

704.1 Inlet Fittings . . . . . . . . . . . . . . . . .168

704.2 Single Vertical Drainage Pipe . . . .168

704.3 Commercial Sinks . . . . . . . . . . . . .168

Table 703.2 Maximum Unit Loading and Maximum Length of Drainage and Vent Piping . . . . . . . . . . . . . .169

705.0 Joints and Connections . . . . . . . .169

705.1 ABS and ABS Co-Extruded

Plastic Pipe and Joints . . . . . . . . .169

705.2 Cast-Iron Pipe and Joints . . . . . . .169

705.3 Copper or Copper Alloy Pipe (DWV) and Joints . . . . . . . . .170

705.4 Galvanized Steel Pipe and Joints . . . . . . . . . . . . . . . . . . .170

705.5 Polyethylene (PE) Sewer Pipe . . .170

CPC § 704.0 Medium relevance — show source text

704.0 Fixture Connections (Drainage). 704.1 Inlet Fittings. Drainage piping shall be provided with approved inlet fittings for fixture connections, correctly located according to the size and type of fixture proposed to be connected.

704.2 Single Vertical Drainage Pipe. Two fixtures set back-to-back, or side-by-side, within the distance allowed between a trap and its vent, shall be permitted to be served by a single vertical drainage pipe provided that each fixture wastes separately into an approved double-fixture fitting having inlet openings at the same level. 704.3 Commercial Sinks. Pot sinks, scullery sinks, dishwashing sinks, silverware sinks, and other similar fixtures shall be connected directly to the drainage system. A floor drain shall be provided adjacent to the fixture and shall be connected on the sewer side of the sink. No other drainage

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TABLE 703.2

MAXIMUM UNIT LOADING AND MAXIMUM LENGTH OF DRAINAGE AND VENT PIPING

SIZE OF PIPE (inches)	11⁄4	11⁄2	2	3	4	5	6	8	10	12
Maximum Units Drainage Piping1 Vertical Horizontal	1 1	22, 7 17	163 83	484 354	256 2165	600 4285	1380 7205	3600 26405	5600 46805	8400 82005
Maximum Length Drainage Piping Vertical, (feet) Horizontal (unlimited)	45	65	85	212	300	390	510	750	–	–
Vent Piping Horizontal and Vertical6 Maximum Units Maximum Lengths, (feet)	1 45	83 60	24 120	84 212	256 300	600 390	1380 510	3600 750	–	–

For SI units: 1 inch = 25 mm, 1 foot = 304.8 mm

Notes: 1 Excluding trap arm. 2 Except for sinks, urinals, and dishwashers – exceeding 1 fixture unit. 3 Except for six-unit traps or water closets.

CPC § 301.3. Medium relevance — show source text

form plumbing design work. Details are necessary to ensure compliance with the requirements of this section, together with a full description of the complete installation including quality, grade of materials, equipment, construction, and methods of assembly and installation. Components, materials, and equipment shall comply with standards and specifications listed in Chapter 17 of this code or approved by the Authority Having Jurisdiction and other national consensus standards applicable to plumbing systems and materials. Where such standards and specifications are not available, alternate materials and equipment shall be approved in accordance with Section 301.3.

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APPENDIX C

Col1	Col2	TABLE C 401.1 SIZE AND LENGTH OF VENTS	Col4	Col5	Col6	Col7	Col8	Col9	Col10	Col11
SIZE OF SOIL OR WASTE STACK (inches)	FIXTURE UNITS CONNECTED	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)	DIAMETER OF VENT REQUIRED (inches)
SIZE OF SOIL OR WASTE STACK (inches)	FIXTURE UNITS CONNECTED	11⁄4	11⁄2	2	21⁄2	3	4	5	6	8
SIZE OF SOIL OR WASTE STACK (inches)	FIXTURE UNITS CONNECTED	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)	MAXIMUM LENGTH OF VENT (feet)
11⁄2	8	50	150	––	––	––	––	––	––	––
2	12	30	75	200	––	––	––	––	––	––
2	20	26	50	150	––	––	––	––	––	––
21⁄2	42	––	30	1

CPC § 304.3.1 Medium relevance — show source text
be sized based on the total accumulated connected load at each story or branch interval.

C 304.3.1 Horizontal Stack Offsets. Horizontal

stack offsets shall be sized in accordance with Table C 304.2 as required for building drains.

C 304.3.2 Vertical Stack Offsets. Vertical stack off sets shall be sized in accordance with Table C 304.3 as required for stacks.

C 304.4 Horizontal Stack Offset and Horizontal Branch

Connections. Horizontal branch connections shall not connect to a horizontal stack offset or within 2 feet (610 mm) above or below the offset where such horizontal offset is located more than four branch intervals below the top of the stack.

C 401.0 Vent System Sizing. C 401.1 Size of Vents. The size of vent piping shall be determined from the developed length and the total number of drainage fixture units connected in accordance with Table C 401.1. Vents shall be not less than one-half the required size of the drainage pipe size served as determined by Table C 304.3 for horizontal fixture branches and stacks nor less than 1 [1] ⁄ 4 inches

(32 mm) in diameter. The drainage system shall be vented by not less than one vent pipe which shall be not less than one-half the size of the required building drain and which shall extend from the building drain or extension of building drain to the outdoors. Vents shall be installed in accordance with Chapter 9. C 401.2 Vent Stack. A vent stack shall be required for a drainage stack that extends five or more branch intervals above the building drain or horizontal branch. The developed length of the vent stack shall be measured from the lowest connection of a branch vent to the termination outdoors.

C 401.3 Branch Vents. Where branch vents exceed 40 feet (12 192 mm) in developed length, such vent shall be increased by one pipe size for the entire developed length of the vent pipe. C 401.4 Venting Horizontal Offsets. Drainage stacks with horizontal offsets shall be vented where five or more branch intervals are located above the offset. The upper and lower section of the horizontal offset shall be vented in accordance

with Section C 401.4.1 and Section C 401.4.2.

C 401.4.1 Venting Upper Section. The vent for the upper section of the stack shall be vented as a separate stack with a vent stack connection installed at the base of the drainage stack. Such vent stack shall connect below the lowest horizontal branch or building drain. Where vent stack connects to the building drain, the connection shall be located downstream of the drainage stack and within a distance of 10 times the diameter of the drainage stack. C 401.4.2 Venting Lower Section. The vent for the lower section of the stack shall be vented by a yoke vent connecting between the offset and the next lower horizontal branch using a wye-branch fitting. The size of the yoke vent and connection shall be not less in diameter

388 2025 CALIFORNIA PLUMBING CODE

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APPENDIX C

TABLE C 303.3 DRAINAGE FIXTURE UNIT VALUES (DFU) FOR BATHROOM GROUPS [1, 2]
California Plumbing Code High relevance — show source text
OF VENT REQUIRED (inches)| |SIZE OF
SOIL OR
WASTE
STACK
(inches)|FIXTURE
UNITS
CONNECTED|11⁄4|11⁄2|2|21⁄2|3|4|5|6|8| |SIZE OF
SOIL OR
WASTE
STACK
(inches)**|FIXTURE
UNITS
CONNECTED|MAXIMUM LENGTH OF VENT (feet)|MAXIMUM LENGTH OF VENT (feet)|MAXIMUM LENGTH OF VENT (feet)|MAXIMUM LENGTH OF VENT (feet)|MAXIMUM LENGTH OF VENT (feet)|MAXIMUM LENGTH OF VENT (feet)|MAXIMUM LENGTH OF VENT (feet)|MAXIMUM LENGTH OF VENT (feet)|MAXIMUM LENGTH OF VENT (feet)| |11⁄2|8|50|150|––|––|––|––|––|––|––| |2|12|30|75|200|––|––|––|––|––|––| |2|20|26|50|150|––|––|––|––|––|––| |21⁄2|42|––|30|100|300|––|––|––|––|––| |3|10|––|30|100|100|600|––|––|––|––| |3|30|––|––|60|200|500|––|––|––|––| |3|60|––|––|50|80|400|––|––|––|––| |4|100|––|––|35|100|260|1000|––|––|––| |4|200|––|––|30|90|250|900|––|––|––| |4|500|––|––|20|70|180|700|––|––|––| |5|200|––|––|––|35|80|350|1000|––|––| |5|500|––|––|––|30|70|300|900|––|––| |5|1100|––|––|––|20|50|200|700|––|––| |6|350|––|––|––|25|50|200|400|1300|––| |6|62

CPC § 0.06 Medium relevance — show source text

INTERMITTENT FLOW ONLY*

GPM	FIXTURE UNITS
Up to 71⁄2	Equals 1 Fixture Unit
Greater than 71⁄2 to 15	Equals 2 Fixture Units
Greater than 15 to 30	Equals 4 Fixture Units
Greater than 30 to 50	Equals 6 Fixture Units

For SI units: 1 gallon per minute = 0.06 L/s

Discharge capacity exceeding 50 gallons per minute (3.15 L/s) shall be determined by the Authority Having Jurisdiction.

702.3 Continuous Flow. For a continuous flow into a drainage system, such as from a pump, sump ejector, air conditioning equipment, or similar device, 2 fixture units shall be equal to each gallon per minute (gpm) (L/s) of flow.

703.0 Size of Drainage Piping. 703.1 Minimum Size. The minimum sizes of vertical, horizontal, or both drainage piping shall be determined from the total of fixture units connected thereto, and additionally, in the case of vertical drainage pipes, in accordance with their length.

703.2 Maximum Number of Fixture Units. Table 703.2

shows the maximum number of fixture units allowed on a vertical or horizontal drainage pipe, building drain, or building sewer of a given size; the maximum number of fixture units allowed on a branch interval of a given size; and the maximum length (in feet and meters) of a vertical drainage pipe of a given size. 703.3 Sizing per Appendix C. For alternate method of sizing drainage piping, see Appendix C.

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TABLE 703.2

MAXIMUM UNIT LOADING AND MAXIMUM LENGTH OF DRAINAGE AND VENT PIPING

SIZE OF PIPE (inches)	11⁄4	11⁄2	2	3	4	5	6	8	10	12
Maximum Units Drainage Piping1 Vertical Horizontal	1 1	22,

CPC § 803.2 Medium relevance — show source text
Solution:

Table 803.2(2) should be used to size single-wall metal vent connectors attached to Type B vertical vents. In the vent connector capacity portion of Table 803.2(2), find the row associated with a 30 foot (9144 mm) vent height. For a 2 foot (610 mm) rise on the vent connector for the water heater, read the shaded columns for draft hood-equipped appliances to find that a 3 inch (76 mm) diameter vent connector has a capacity of 37 000 Btu/h (10.8 kW). Therefore, a 3 inch (76 mm) single-wall metal vent connector can be used with the water heater. For a draft hood-equipped furnace with a 3 foot (914 mm) rise, read across the appropriate row to find that a 5 inch (127 mm) diameter vent connector has a maximum capacity of 120 000 Btu/h (35 kW) (which is too small for the furnace), and a 6 inch (152 mm) diameter vent connector has a maximum vent capacity of 172 000 Btu/h (50 kW). Therefore, a 6 inch (152 mm) diameter vent connector should be used with the 150 000 Btu/h (44 kW) furnace. Because both vent connector horizontal lengths are less than the maximum lengths listed in Section 803.2.1, the table values can be used without adjustments.

In the common vent capacity portion of Table 803.2(2), find the row associated with a 30 foot (9144 mm) vent height and read over to the NAT + NAT portion of the 6 inch (152 mm) diameter column to find a maximum combined capacity of 257 000 Btu/h (75 kW). Since the two appliances total only 185 000 Btu/h (54 kW), a 6 inch (152 mm) common vent can be used. [NFPA 54:F.2.1]

F 102.2 Example 5(a): Common Venting a Draft Hood-Equipped Water Heater with a Fan-Assisted Furnace into a Type B Vent. In this case, a 35 000 Btu/h (10.3 kW) input draft hood-equipped water heater with a 4 inch (102 mm) diameter draft hood outlet, 2 feet (610 mm) of connector rise, and 4 feet (1219 mm) of horizontal length is to be common vented with a 100 000 Btu/h (29 kW) fanassisted furnace with a 4 inch (102 mm) diameter flue collar, 3 feet (914 mm) of connector rise, and 6 feet (1829 mm) of horizontal length. The common vent consists of a 30 foot (9144 mm) height of Type B vent. What are the recommended vent diameters for each connector and the common vent? The installer would like to use a single-wall metal vent connector. (See Figure F 102.2)

Solution:

Water Heater Vent Connector Diameter. Since the water heater vent connector horizontal length of 4 feet (1219 mm) is less than the maximum value listed in Table 803.2(2), the venting table values can be used without adjustments.
CPC § 1.3 Medium relevance — show source text
[NFPA 54:F.1.3]

G 101.6 Example 4: Common Venting Two Draft Hood-Equipped Appliances. A 35 000 Btu/h (10.3 kW) water heater is to be common vented with a 150 000 Btu/h (44 kW) furnace, using a common vent with a total height of 30 feet (9144 mm). The connector rise is 2 feet (610 mm) for the water heater with a horizontal length of 4 feet (1219 mm). The connector rise for the furnace is 3 feet (914 mm) with a

2025 CALIFORNIA PLUMBING CODE 429

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APPENDIX G

horizontal length of 8 feet (2438 mm). Assume single-wall metal connectors will be used with Type B vent. What size connectors and combined vent should be used in this installation? (See Figure G 101.6)

Solution:

Table 510.2(2) should be used to size single-wall metal vent connectors attached to Type B vertical vents. In the vent connector capacity portion of Table 510.2(2), find the row associated with a 30 foot (9144 mm) vent height. For a 2 foot (610 mm) rise on the vent connector for the water heater, read the shaded columns for draft hood-equipped appliances to find that a 3 inch (76 mm) diameter vent connector has a capacity of 37 000 Btu/h (10.8 kW). Therefore, a 3 inch (76 mm) single-wall metal vent connector can be used with the water heater. For a draft hood-equipped furnace with a 3 foot (914 mm) rise, read across the appropriate row to find that a 5 inch (127 mm) diameter vent connector has a maximum capacity of 120 000 Btu/h (35 kW) (which is too small for the furnace) and a 6 inch (152 mm) diameter vent connector has a maximum vent capacity of 172 000 Btu/h (50 kW). Therefore, a 6 inch (152 mm) diameter vent connector should be used with the 150 000 Btu/h (44 kW) furnace. Because both vent connector, horizontal lengths are less than the maximum lengths listed in Section 510.2.1; the table values can be used without adjustments.

In the common vent capacity portion of Table 510.2(2), find the row associated with a 30 foot (9144 mm) vent height and read over to the NAT + NAT portion of the 6 inch (152 mm) diameter column to find a maximum combined capacity of 257 000 Btu/h (75 kW). Since the two appliances total only 185 000 Btu/h (54 kW), a 6 inch (152 mm) common vent can be used. [NFPA 54:F.2.1]

For SI units: 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW

FIGURE G 101.6

COMMON VENTING TWO DRAFT HOOD-EQUIPPED

APPLIANCES – EXAMPLE 4

[NFPA 54: FIGURE F.2.1]

CPC § 803.2 Medium relevance — show source text

803.2 Additional Requirements to Multiple-Appliance Vent. Venting Table 803.2(1) through Table 803.2(9) shall not be used where obstructions are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer’s instructions, or in accordance with the following:

(1) The maximum capacity of the vent connector shall be determined using the NAT Max column.

(2) The maximum capacity of the vertical vent or chimney shall be determined using the FAN + NAT column when the second appliance is a fan-assisted appliance, or the NAT + NAT column when the second appliance is equipped with a draft hood.

(3) The minimum capacity shall be determined as if the appliance were a fan-assisted appliance, as follows:

(a) The minimum capacity of the vent connector shall be determined using the FAN Min column.

803.2.1 Vent Connector Maximum Length. The maximum vent connector horizontal length shall be 18 inches per inch (18 mm/mm) of connector diameter as shown in Table 803.2.1, or as permitted by Section 803.2.2. [NFPA 54:13.2.2]

TABLE 803.2.1

VENT CONNECTOR MAXIMUM LENGTH

[NFPA 54: TABLE 13.2.2]

CONNECTOR DIAMETER (inches)	MAXIMUM CONNECTOR HORIZONTAL LENGTH (feet)
3	41⁄2
4	6
5	71⁄2
6	9
7	101⁄2
8	12
9	131⁄2
10	15
12	18
14	21
16	24
18	27
20	30
22	33
24	36

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm

TABLE 803.2.1

VENT CONNECTOR MAXIMUM LENGTH

CPC § 510.2.1 Medium relevance — show source text

TABLE 510.2.1

VENT CONNECTOR MAXIMUM LENGTH

[NFPA 54: TABLE 13.2.2]

CONNECTOR DIAMETER (inches)	MAXIMUM CONNECTOR HORIZONTAL LENGTH (feet)
3	41⁄2
4	6
5	71⁄2
6	9
7	101⁄2
8	12
9	131⁄2
10	15
12	18
14	21
16	24
18	27
20	30
22	33
24	36

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm

510.2.2 Vent Connector Exceeding Maximum Length. The vent connector shall be routed to the vent utilizing the shortest possible route. Connectors with longer horizontal lengths than those listed in Table 510.2.1 are permitted under the following conditions:

(1) The maximum capacity (FAN Max or NAT Max) of the vent connector shall be reduced 10 percent for each additional multiple of the length listed in Table 510.2.1. For example, the maximum length listed for a 4 inch (100 mm) connector is 6 feet (1829 mm). With a connector length greater than 6 feet (1829 mm) but not exceeding 12 feet (3658 mm), the maximum capacity must be reduced by 10 percent (0.90 x maximum vent connector capacity). With a connector length greater than 12 feet (3658 mm) but not exceeding 18 feet (5486 mm), the maximum capacity shall be reduced by 20 percent (0.80 x maximum vent capacity).

TABLE 510.2.1

VENT CONNECTOR MAXIMUM LENGTH

[NFPA 54: TABLE 13.2.2]

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm

106 2025 CALIFORNIA PLUMBING CODE

WATER HEATERS

(2) For a connector serving a fan-assisted appliance, the minimum capacity (FAN Min) of the connector shall be determined by referring to the corresponding single appliance table. For Type B double-wall connectors, Table 510.1.2(1) shall be used. For single-wall connectors, Table 510.1.2(2) shall be used. The height ( H ) and lateral ( L ) shall be measured according to the procedures for a single appliance vent, as if the other appliances were not present. [NFPA 54:13.2.3]

CPC § 510.1.17 Medium relevance — show source text

510.1.17 Height Entries. Where the actual height of a vent falls between entries in the height column of the applicable table in Table 510.1.2(1) through Table 510.1.2(6), either of the following shall be used:

(1) Interpolation.

(2) The lower appliance input rating shown in the table entries for FAN Max and NAT Max column values; and the higher appliance input rating for the FAN Min column values. [NFPA 54:13.1.18]

510.2 Additional Requirements to Multiple-Appliance Vent. Venting Table 510.2(1) through Table 510.2(9) shall not be used where obstructions are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer’s instructions, or in accordance with the following:

(1) The maximum capacity of the vent connector shall be determined using the NAT Max column.

(3) The minimum capacity shall be determined as if the appliance were a fan-assisted appliance, as follows:

(a) The minimum capacity of the vent connector shall be determined using the FAN Min column.

(b) The FAN + FAN column shall be used when the second appliance is a fan-assisted appliance, and the FAN + NAT column shall be used when the second appliance is equipped with a draft hood, to determine whether the vertical vent or chimney configuration is not permitted (NA). Where the vent configuration is NA, the vent configuration shall not be permitted and an alternative venting configuration shall be utilized. [NFPA 54:13.2.1] 510.2.1 Vent Connector Maximum Length. The maximum vent connector horizontal length shall be 18 inches per inch (18 mm/mm) of connector diameter as shown in Table 510.2.1, or as permitted by Section 510.2.2. [NFPA 54:13.2.2]

TABLE 510.2.1

VENT CONNECTOR MAXIMUM LENGTH

[NFPA 54: TABLE 13.2.2]

CONNECTOR DIAMETER (inches)	MAXIMUM CONNECTOR HORIZONTAL LENGTH (feet)
3	41⁄2
4	6
5	71⁄2
6	9
7	101⁄2
8	12
9	131⁄2
10	15
12	18
14	21
16	24
18	27
20	30
22	33
24	36

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm

Frequently asked questions

What is the minimum vent diameter I can use?

Minimum vent diameter is 1 1/4 inches; an individual vent must also be at least one-half the diameter of the drain it serves. See § 703.2 and Appendix C for details.

How much of a vent can be horizontal?

No more than one-third of the permitted developed length of a vent may be installed in a horizontal position (Table 703.2 note). § 703.2.

When do I have to increase vent size for length?

If a branch vent’s developed length exceeds 40 ft, Appendix C requires increasing the vent one pipe size for the entire developed length. § C 401.3.

Do the Table 703.2 length limits always apply?

If the vent is increased by one pipe size for its entire length, the table’s maximum length limits do not apply (Table 703.2 note). § 703.2.

Where do I get fixture-unit values?

Use Table 702.1 (Drainage Fixture Unit values) and Table 702.2 for intermittent/continuous flows to compute DFU before using Table 703.2. § 702.1.

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