CPC · California Plumbing Code

How do I account for pressure loss, devices, and maximum velocities in design?

Q: How do I get device ΔP when manufacturer data is missing?

If manufacturer ΔP is not available, § 610.2 requires the device inlet/outlet diameter be at least the distribution pipe diameter so you don't create an uncontrolled restriction; alternatively, use a conservative replacement device with known performance or seek AHJ approval for engineering assumptions.

Q: Are copper velocity limits different for hot and cold?

Yes: for copper systems cold water is limited to 8 ft/s and hot water to 5 ft/s per § 610.12 . Check both hot and cold branches where applicable.

You must include the pressure drop of any in‑line device (filters, softeners, backflow preventers, tankless heaters, etc.) in your water‑supply head‑loss calculations and size the meter and piping to deliver the required flow and residual pressure; use Appendix A friction charts for pipe losses and ensure copper systems do not exceed **8 ft/s** cold or **5 ft/s** hot, unless an AHJ‑accepted engineered design or an exception applies (see **§ 610.2**, **§ 610.6**, **§ 610.12**, **§ 610.13**).

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

In plain terms: include the pressure drop of any in-line devices (filters, softeners, backflow preventers, tankless heaters, etc.) in your system pressure‑loss calculations and size the meter and supply piping to deliver the required flow and residual pressure. That friction and device loss information is to be taken from Appendix A friction charts or manufacturer data, and water piping velocities must not exceed the maximums listed for the material. These requirements are set out in § 610.2, § 610.6, and § 610.12 of the CPC, with limited exceptions listed at § 610.13.

Include device pressure loss in the system head‑loss calculation and keep flow velocities at or below the code limits for the pipe material.

Requirements in detail

1) Devices — what the code requires you to include

The pressure loss through a water filter, water softener, backflow prevention device, tankless water heater, or similar device must be included in the system pressure‑loss calculations and the meter/supply sized accordingly (§ 610.2).
If you lack published pressure‑drop data for a device, the code requires that the inlet or outlet diameter of that device (or its connecting piping) be not less than the diameter of the water distribution piping to the fixtures served (i.e., do not create a smaller throat that will produce an unknown/excessive drop) (§ 610.2).
Devices must be of a type approved by the AHJ and, where applicable, tested for flow rating and pressure loss by an approved lab. § 610.2 requires documented flow/pressure‑loss info or conservative sizing.

2) Friction, fittings, and where to get loss data

Use the “Fairly Rough” or “Rough” charts in Appendix A for friction‑loss data, unless the pipe material/water quality indicates no loss with service time. Friction losses for meters, valves, and fittings are to be obtained from the same Appendix A sources; device losses computed per § 610.2 (§ 610.6).
In short: assemble total available pressure at the meter, subtract elevation head, subtract meter loss, subtract device losses, then use the remainder for pipe friction sizing (Appendix A charts and tables).

3) Maximum velocities (material limits)

For copper and copper‑alloy tube/fitting systems, the code caps velocities at 8 ft/s (2.4 m/s) for cold water and 5 ft/s (1.5 m/s) for hot water (§ 610.12.1).
For tubing using copper fittings (tubing other than copper but using copper fittings), the same 8 ft/s / 5 ft/s limits apply through the fittings (§ 610.12.2).

Decision‑relevant dimensions / values (quick reference table)

Item	Decision metric / value to use	Typical engineering action	Code Reference
Include device pressure loss	Always include device ΔP in system calculations	Obtain manufacturer ΔP @ design flow; if unavailable, size device inlet/outlet ≥ distribution pipe dia.	§ 610.2
Friction data source	Use Appendix A “Fairly Rough” / “Rough” charts	Read friction (ft/100 ft) for pipe material & Q, convert to psi	§ 610.6 & Appendix A
Max velocity (copper systems)	Cold: 8 ft/s (2.4 m/s); Hot: 5 ft/s (1.5 m/s)	Check Q vs. pipe area; increase pipe size if v > limit	§ 610.12.1
Unknown device data	Inlet/outlet diameter ≥ distribution piping	Prevent an unquantified, excessive pressure drop	§ 610.2
Exceptions	Systems sized via recognized engineering procedures accepted by AHJ	Submit calculations to AHJ; exceptions available per § 610.13	§ 610.13

Exceptions & special cases

The size/velocity provisions do not apply when the system is designed in accordance with recognized engineering procedures acceptable to the Authority Having Jurisdiction (AHJ) — e.g., full hydraulic calculations are submitted and accepted (§ 610.13 (1)).
Minor alterations, replacements, piping that is part of fixture equipment, and other situations judged by the AHJ to provide adequate water are excepted (§ 610.13 (2)–(5)).
Irrigation piping outside of a building that is separated from potable water by an approved backflow/air‑gap is not regulated for size/material by this chapter, but the potable supply feeding it must still be sized to deliver combined demand (§ 610.13 (6)).

Note: an AHJ may still require manufacturer ΔP data or conservative measures even when an exception is claimed.

Common mistakes

Relying on nominal pipe size without adding published device ΔP (filters, softeners, backflow) — code requires inclusion in the system calculation (§ 610.2).
Using the wrong friction chart or failing to adjust for “fairly rough” vs. “rough” conditions (Appendix A) — this underestimates head loss for older or fouling‑prone systems (§ 610.6).
Forgetting to check velocity limits (especially in copper systems), which can cause noise, erosion, accelerated wear, or code noncompliance (§ 610.12) .
Installing a device with smaller inlet/outlet than the downstream distribution pipe when device ΔP is unknown — the code forbids creating an unquantified excessive pressure drop (§ 610.2).

Worked example — single‑line building supply with a backflow preventer

Scenario: You are designing the building supply for a small commercial tenant. Required peak flow to the building = 30 gpm. Meter is at grade and the highest fixture is 15 ft above the meter. The supply includes a listed backflow prevention device whose published ΔP at 30 gpm is 6 psi. You plan to use copper tube for the branch run.

Step 1 — Elevation loss

Elevation difference = 15 ft → static head = 15 × 0.433 = 6.5 psi loss (downward signed as gain or loss depending on sign convention; code uses 0.43 psi/ft in Appendix A guidance) — account per § 610.8/Appendix A.

Step 2 — Device loss (must be included)

Backflow ΔP = 6 psi at 30 gpm per manufacturer — include per § 610.2.

Step 3 — Available service pressure example (assume)

Assume water main provides 60 psi at meter. Subtract elevation head and device loss: 60 − 6.5 − 6 = 47.5 psi left for meter + meter loss + pipe friction.

Step 4 — Meter and friction allowance

Suppose the selected meter at 30 gpm has a published loss of 3 psi → remaining for pipe friction = 47.5 − 3 = 44.5 psi. Use Appendix A charts to select pipe size so friction over the developed length does not exceed 44.5 psi. (Appendix A gives friction in ft/100 ft; convert to psi using 0.433 ft water/psi or use the head‑loss formula in Appendix A.)

Step 5 — Velocity check for copper (must not exceed code max)

Example pick: 1‑inch copper nominal ID ≈ 0.7854 in² (table of areas in CPC Useful Tables). Convert 30 gpm to cubic feet per second: 30 gpm = 30 × 0.002228 = 0.06684 ft³/s. Area of 1" in ft² = 0.7854 in² × (1 ft² / 144 in²) = 0.005455 ft². Velocity v = Q / A = 0.06684 / 0.005455 ≈ 12.25 ft/s. That exceeds the 8 ft/s cold‑water limit for copper (§ 610.12.1), so 1" is too small.
Try 1‑1/4" copper (area ≈ 1.227 in² → 0.00852 ft²): v = 0.06684 / 0.00852 ≈ 7.85 ft/s which meets the 8 ft/s cold limit. Choose 1‑1/4" copper and then verify friction from Appendix A over the developed length to ensure the friction loss fits inside the remaining 44.5 psi.

Bottom line: because the device ΔP (6 psi) and elevation head (6.5 psi) materially reduce available pressure, you must both (a) include those losses per § 610.2/§ 610.6, and (b) size the piping large enough to keep both friction and velocity within code limits (§ 610.12).

Related provisions

§ 610.1 — Size of each water meter and potable supply pipe; overall sizing requirement.
§ 610.4 — Use of Table 610.4 for system sizing and limits on velocities when using listed parallel distribution systems.
§ 610.5 — Sizing methods including Appendix A procedures (reference for engineering sizing).
Appendix A (A104 / A105) — Friction‑loss charts (“Fairly Rough” / “Rough”), developed length and friction calculation procedures used by § 610.6.
§ 611.1 — Requirements for drinking water treatment units (applies to device approvals, sizing and connections).

Code references

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

CPC § 609.12.3 High relevance — show source text
(2) Hot water piping between the fixture control valve or supply stop and the fixture or appliance shall not be required to be insulated. 609.12.3 California Energy Code Pipe Insulation Requirements. [CEC] See California Energy Code Sec- tions 150.0(j)2 and 120.3(c) for pipe insulation require- ments based on fluid temperature and pipe diameter – for domestic hot water piping. The California Energy Code requires that piping that penetrates metal framing shall use grommets, plugs, wrapping or other insulating mate- rial to assure that no contact is made with the metal fram- ing. The California Energy Code also requires that insulation shall abut securely against all framing mem- bers, and places conditions on when installed wall or attic insulation that surrounds installed piping can be consid- ered to provide pipe insulation meeting requirements.

610.0 Size of Potable Water Piping. 610.1 Size. The size of each water meter and each potable water supply pipe from the meter or other source of supply to the fixture supply branches, risers, fixtures, connections, outlets, or other uses shall be based on the total demand and shall be determined according to the methods and procedures outlined in this section. Water piping systems shall be designed to ensure that the maximum velocities allowed by the code and the applicable standard are not exceeded.

610.2 Pressure Loss. Where a water filter, water softener, backflow prevention device, tankless water heater, or similar device is installed in a water supply line, the pressure loss through such devices shall be included in the pressure loss calculations of the system, and the water supply pipe and meter shall be adequately sized to provide for such a pressure loss.

No water filter, water softener, backflow prevention device, or similar device regulated by this code shall be installed in a potable water supply piping where the installation of such device produces an excessive pressure drop in such water supply piping. In the absence of specific pressure drop information, the diameter of the inlet or outlet of such device or its connecting piping shall be not less than the diameter of such water distribution piping to the fixtures served by the device.

156 2025 CALIFORNIA PLUMBING CODE

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WATER SUPPLY AND DISTRIBUTION

Such devices shall be of a type approved by the Authority Having Jurisdiction and shall be tested for flow rating and pressure loss by an approved laboratory or recognized testing agency to standards consistent with the intent of this chapter. 610.3 Quantity of Water. The quantity of water required to be supplied to every plumbing fixture shall be represented by fixture units, as shown in Table 610.3. Equivalent fixture values shown in Table 610.3 include both hot and cold water demand.

610.4 Sizing Water Supply and Distribution Systems. Systems within the range of Table 610.4 shall be permitted to be sized from that table or by the method in accordance with Section 610.5.

Listed parallel water distribution systems shall be installed in accordance with their listing, but at no time shall a portion of the system exceed the maximum velocities allowed by the code. 610.5 Sizing per Appendices A, C, and M **.
CPC § 610.3 High relevance — show source text
No water filter, water softener, backflow prevention device, or similar device regulated by this code shall be installed in a potable water supply piping where the installation of such device produces an excessive pressure drop in such water supply piping. In the absence of specific pressure drop information, the diameter of the inlet or outlet of such device or its connecting piping shall be not less than the diameter of such water distribution piping to the fixtures served by the device.

156 2025 CALIFORNIA PLUMBING CODE

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WATER SUPPLY AND DISTRIBUTION

Such devices shall be of a type approved by the Authority Having Jurisdiction and shall be tested for flow rating and pressure loss by an approved laboratory or recognized testing agency to standards consistent with the intent of this chapter. 610.3 Quantity of Water. The quantity of water required to be supplied to every plumbing fixture shall be represented by fixture units, as shown in Table 610.3. Equivalent fixture values shown in Table 610.3 include both hot and cold water demand.

610.4 Sizing Water Supply and Distribution Systems. Systems within the range of Table 610.4 shall be permitted to be sized from that table or by the method in accordance with Section 610.5.

Listed parallel water distribution systems shall be installed in accordance with their listing, but at no time shall a portion of the system exceed the maximum velocities allowed by the code. 610.5 Sizing per Appendices A, C, and M . Except as provided in Section 610.4, the size of each water piping system shall be determined in accordance with the procedure set forth in Appendix A. For alternative methods of sizing water supply systems, see Appendix C or Appendix M . 610.6 Friction and Pressure Loss. Except where the type of pipe used and the water characteristics are such that no decrease in capacity due to the length of service (age of system) is expected, friction-loss data shall be obtained from the “Fairly Rough” or “Rough” charts in Appendix A of this code. Friction or pressure losses in a water meter, valve, and fittings shall be obtained from the same sources. Pressure losses through water-treating equipment, backflow prevention devices, or other flow-restricting devices shall be computed in accordance with Section 610.2. 610.7 Conditions for Using Table 610.4. On a proposed water piping installation sized using Table 610.4, the following conditions shall be determined:

(1) Total number of fixture units as determined from Table 610.3, Equivalent Fixture Units, for the fixtures to be installed.

(2) Developed length of supply pipe from meter to the most remote outlet.

(3) Difference in elevation between the meter or other source of supply and the highest fixture or outlet.

(4) Pressure in the street main or another source of supply at the locality where the installation is to be made.

(5) In localities where there is a fluctuation of pressure in the main throughout the day, the water piping system shall be designed on the basis of the minimum pressure available. 610.8 Size of Meter and Building Supply Pipe Using Table 610.4. The size of the meter and the building supply pipe shall be determined as follows:

(1) Determine the available pressure at the water meter or other source of supply.
CPC § 609.11 High relevance — show source text
(b) Where occupancy is delayed four weeks after disin- fection, disinfection and flushing shall again be com- pleted. 609.11 Water Hammer. [Not adopted by HCD] Building water supply systems where quick-acting valves are installed shall be provided with water hammer arrester(s) to absorb high pressures resulting from the quick closing of these valves. Water hammer arresters shall be approved mechanical devices that comply with ASSE 1010 or PDI-WH 201 and shall be installed as close as possible to quick-acting valves.

609.11.1 Mechanical Devices. Where listed mechanical devices are used, the manufacturer’s specifications as to location and method of installation shall be followed.

609.12 Pipe Insulation. Insulation of domestic hot water piping shall be in accordance with Section 609.12.1 and Section 609.12.2.

609.12.1 Insulation Requirements. Domestic hot water piping shall be insulated. 609.12.2 Pipe Insulation Wall Thickness. Hot water pipe insulation shall have a minimum wall thickness of not less than the diameter of the pipe for a pipe up to 2 inches (50 mm) in diameter. Insulation wall thickness shall be not less than 2 inches (51 mm) for a pipe of 2 inches (50 mm) or more in diameter. Exceptions: (1) Piping that penetrates framing members shall not be required to have pipe insulation for the distance of the framing penetration. (2) Hot water piping between the fixture control valve or supply stop and the fixture or appliance shall not be required to be insulated. 609.12.3 California Energy Code Pipe Insulation Requirements. [CEC] See California Energy Code Sec- tions 150.0(j)2 and 120.3(c) for pipe insulation require- ments based on fluid temperature and pipe diameter – for domestic hot water piping. The California Energy Code requires that piping that penetrates metal framing shall use grommets, plugs, wrapping or other insulating mate- rial to assure that no contact is made with the metal fram- ing. The California Energy Code also requires that insulation shall abut securely against all framing mem- bers, and places conditions on when installed wall or attic insulation that surrounds installed piping can be consid- ered to provide pipe insulation meeting requirements.

610.0 Size of Potable Water Piping. 610.1 Size. The size of each water meter and each potable water supply pipe from the meter or other source of supply to the fixture supply branches, risers, fixtures, connections, outlets, or other uses shall be based on the total demand and shall be determined according to the methods and procedures outlined in this section. Water piping systems shall be designed to ensure that the maximum velocities allowed by the code and the applicable standard are not exceeded.

610.2 Pressure Loss. Where a water filter, water softener, backflow prevention device, tankless water heater, or similar device is installed in a water supply line, the pressure loss through such devices shall be included in the pressure loss calculations of the system, and the water supply pipe and meter shall be adequately sized to provide for such a pressure loss.

CPC § 1323.1.4 High relevance — show source text

1323.1.4 Maximum Demand. Where the maximum demand for each medical gas or vacuum system does not exceed the values in Table 1323.1.4(1) through Table 1323.1.4(6), the size of pipe of each section of the system shall be determined in accordance with Section 1323.1.5. The size for systems beyond the range of Table 1323.1.4(1) through Table 1323.1.4(6) shall be determined in accordance with Section 1323.1.6.

1323.1.5 Sizing Procedures. The size of each section of pipe in a system within the range of Table 1323.1.4(1) through Table 1324.1.4(6) shall be determined in accordance with the following:

(1) Determine the total flow rate and number of outlets or inlets for each section of pipe in accordance with Table 1305.2 and Table 1305.3.

(2) Measure the length of the section of pipe to each station outlet or inlet on the system. Multiply the measured pipe length by 1.5 (150 percent), to account for the number of fittings in the system, to determine the pipe equivalent length.

(3) Beginning with the most remote outlet or inlet, multiply the total flow rate by the diversity factor specified in Table 1323.1.5(1) for each section of pipe to determine the sizing flow rate for the piping.

(4) Select Table 1323.1.4(1) through Table 1324.1.4(6) based on the medical gas or vacuum being transported through the piping.

(5) Select an estimated pipe size for determining the system pressure loss. Multiply the pipe equivalent length, for a given section of pipe, by the pressure loss for the sizing flow rate in the applicable table. Divide that number by 100 to determine the system pressure loss for the section of pipe.

(6) Add the pressure loss for each section of piping, from the source equipment location to the outlet or

inlet, to determine the total system pressure loss to each outlet or inlet. The total system pressure loss in the piping to each outlet or inlet shall not exceed the values specified in Table 1323.1.5(2).

TABLE 1323.1.5(1) SYSTEM SIZING – FLOW REQUIREMENTS FOR STATION OUTLETS AND INLETS [1]

NUMBER OF OUTLETS AND INLETS TERMINAL UNITS PER FACILITY	DIVERSITY PERCENTAGE OF AVERAGE FLOW PER OUTLETS AND INLETS TERMINAL UNITS	MINIMUM PERMISSIBLE SYSTEM FLOW OF ALL PRESSURIZED MEDICAL GAS SYSTEMS2 (standard cubic feet per minute)
1–10	100%	Actual Demand
11–25	75%	7.0
26–50	50%	13.1
51–100	50%	17.5

Notes: 1 Flow rates of station outlets and inlets in accordance with Table 1305.2. 2 The minimum system flow is the average outlets and inlets flow times the number of station outlets and inlets times the diversity percentage.

TABLE 1323.1.5(2) MAXIMUM PERMITTED PRESSURE LOSS IN

CPC § 102.2 High relevance — show source text
CHART A 102.2

FRICTION LOSSES FOR DISK-TYPE WATER METERS

FLOW (gallons per minute)

For SI units: 1 inch = 25 mm, 1 pound-force per square inch = 6.8947 kPa, 1 gallon per minute = 0.06 L/s

2025 CALIFORNIA PLUMBING CODE 367

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APPENDIX A

A 104.2 Elevation. Determine the elevation of the highest fixture or group of fixtures above the water (street) main. Multiply this difference in elevation by 0.43. The result is the loss of static pressure in psi (kPa). A 104.3 Available Pressure. Subtract the sum of loss in static pressure and the residual pressure to be maintained at the highest fixture from the average minimum daily service pressure. The result will be the pressure available for friction loss in the supply pipes, where no water meter is used. Where a meter is to be installed, the friction loss in the meter for the estimated maximum demand should also be subtracted from the service pressure to determine the pressure loss available for friction loss in the supply pipes. A 104.4 Developed Length. Determine the developed length of pipe from the water (street) main to the highest fixture. Where close estimates are desired, compute with the aid of Table A 104.4(1), Table A 104.4(2), or Table A 104.4(3), whichever is applicable, the equivalent length of pipe for fittings in the line from the water (street) main to the highest fixture and add the sum to the developed length. The pressure available for friction loss in psi (kPa), divided by the developed lengths of pipe from the water (street) main to the highest fixture, times 100, will be the average permissible friction loss per 100 feet (30 480 mm) length of pipe.

A 105.0 Size of Building Supply. A 105.1 Diameter. Knowing the permissible friction loss per 100 feet (30 480 mm) of pipe and the total demand, the diameter of the building supply pipe shall be permitted to be obtained from Chart A 105.1(1), Chart A 105.1(2), Chart A 105.1(3), Chart A 105.1(4), Chart A 105.1(5), Chart A 105.1(6), or Chart A 105.1(7), whichever is applicable. The diameter of pipe on or next above the coordinate point corresponding to the estimated total demand and the permissible friction loss will be the size needed up to the first branch from the building supply pipe. A 105.2 Copper and Copper Alloy Piping. Where copper tubing or copper alloy pipe is to be used for the supply piping and where the character of the water is such that slight changes in the hydraulic characteristics are expected, Chart A 105.1(1) shall be permitted to be used. A 105.3 Hard Water. Chart A 105.1(2) shall be used for ferrous pipe with the most favorable water supply in regards to corrosion and caking. Where the water is hard or corrosive, Chart A 105.1(3) or Chart A 105.1(4) will be applicable.
CPC § 0.90 High relevance — show source text
00|0.90|DR|DR|DR| |Minimum
1× wood
furringd|Minimum
2× wood
stud|No.10
wood
screw|1|24|4.00|0.90|DR|DR|DR|2.85|DR|DR|DR|DR| |Minimum
1× wood
furringd|Minimum
2× wood
stud|1/4″
lag screw|11/2|12|4.00|2.65|1.90|1.50|0.90|4.00|1.65|1.05|0.80|DR| |Minimum
1× wood
furringd|Minimum
2× wood
stud|1/4″
lag screw|11/2|16|4.00|1.95|1.25|0.95|0.50|4.00|1.10|0.65|DR|DR| |Minimum
1× wood
furringd|Minimum
2× wood
stud|1/4″
lag screw|11/2|24|4.00|1.10|0.65|DR|DR|3.25|0.50|DR|DR|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa, 1 pound per square inch = 6.895 kPa.
DR = Design Required.
o.c. = On Center.
a. Wood framing and furring shall be Spruce-pine-fir or any wood species with a specific gravity of 0.42 or greater in accordance with AWC NDS.
b. Nail fasteners shall comply with ASTM F1667, except nail length shall be permitted to exceed ASTM F1667 standard lengths.
c. The thickness of wood structural panels complying with the specific gravity requirements of Note a shall be permitted to be included in satisfying the minimum required pene-
tration into framing.
d. Where the required cladding fastener penetration into wood material exceeds3/4 inch and is not more than 11/2 inches, a minimum 2× wood furring or an approved design shall
be used.
e. Foam sheathing shall have a minimum compressive strength of 15 psi in accordance with ASTM C578 or ASTM C1289.
f. Furring shall be spaced not more than 24 inches on center, in a vertical or horizontal orientation. In a vertical orientation, furring shall be located over wall studs and attached
with the required fastener spacing. In a horizontal orientation, the indicated 8-inch and 12-inch fastener spacing in furring shall be achieved by use of two fasteners into studs
at 16 inches and 24 inches on center, respectively.
g. Cladding weight is the maximum weight of cladding materials in pounds per square foot of wall area. The 3 psf category typically applies to panel and lap siding materials; the
11 psf category typically applies to conventional three-coat stucco of7/8-inch thickness; and 15 psf to 25 psf categories typically apply to adhered masonry veneers.|For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa, 1 pound per square inch = 6.895 kPa.
DR = Design Required.
o.c. = On Center.
a.

CPC § 3.4.2 High relevance — show source text

Add 5 gpm to the flow rate required by Section_R309.3.4.2_ where the water service pipe supplies more than one dwelling.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 0.063 L/s, 1 pound per square inch = 6.895 kPa.
NP = Not Permitted. Pressure loss exceeds reasonable limits.
a. Values are applicable for underground piping materials listed in_ the California Plumbing Code_ and are based on an SDR of 11 and a Hazen Williams C Factor of 150.
b. Values include the following length allowances for fittings: 25-percent length increase for actual lengths up to 100 feet and 15-percent length increase for actual lengths over
100 feet.
c. Flow rate from Section P2904.4.2. Add 5 gpm to the flow rate required by Section_R309.3.4.2_ where the water service pipe supplies more than one dwelling.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 0.063 L/s, 1 pound per square inch = 6.895 kPa.
NP = Not Permitted. Pressure loss exceeds reasonable limits.
a. Values are applicable for underground piping materials listed in_ the California Plumbing Code_ and are based on an SDR of 11 and a Hazen Williams C Factor of 150.
b. Values include the following length allowances for fittings: 25-percent length increase for actual lengths up to 100 feet and 15-percent length increase for actual lengths over
100 feet.
c. Flow rate from Section P2904.4.2. Add 5 gpm to the flow rate required by Section_R309.3.4.2_ where the water service pipe supplies more than one dwelling.|

TABLE R309.3.6.2(2)—MINIMUM WATER METER PRESSURE LOSS (PL )a m	Col2	Col3	Col4
FLOW RATE (gallons per minute, gpm)b	5/8-INCH METER PRESSURE LOSS (pounds per square inch, psi)	3/4-INCH METER PRESSURE LESS (pounds per square inch, psi)	1-INCH METER PRESSURE LOSS (pounds per square inch, psi)
8	3	3	1
10	3	3	1
12	4	3	1
14	6	5	1
16	7	6	1
18	9	7	2
20	11	9	2
23	14	11	3
26	18	14	3
31	26	22	4
39	38	35	6
52	NP	NP	10
For SI: 1 inch = 25.4 mm, 1 pound per square inch = 6.895 kPa, 1 gallon per minute = 0.063 L/s. NP = Not permitted unless the actual water meter pressure loss is known. a. Table P2904.6.2(2) establishes conservative values for water meter pressure loss or installations where the water meter loss is unknown. Where the actual water meter pres- sure loss is published and available from the meter manufacturer,PLm shall be the published pressure loss for the selected meter. b.

CPC § 25.4 High relevance — show source text
ML-CL and**
inorganic CL 60| |8|4|NR|NR|NR| |8|5|NR|6 @ 39|6 @ 48| |8|6|5 @ 39|6 @ 48|6 @ 35| |8|7|6 @ 48|6 @ 34|6 @ 25| |8|8|6 @ 39|6 @ 25|6 @ 18| |9|4|NR|NR|NR| |9|5|NR|5 @ 37|6 @ 48| |9|6|5 @ 36|6 @ 44|6 @ 32| |9|7|6 @ 47|6 @ 30|6 @ 22| |9|8|6 @ 34|6 @ 22|6 @ 16| |9|9|6 @ 27|6 @ 17|DR| |10|4|NR|NR|NR| |10|5|NR|5 @ 35|6 @ 48| |10|6|6 @ 48|6 @ 41|6 @ 30| |10|7|6 @ 43|6 @ 28|6 @ 20| |10|8|6 @ 31|6 @ 20|DR| |10|9|6 @ 24|6 @ 15|DR| |10|10|6 @ 19|DR|DR| |For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.1571 kPa2/m, 1 pound per square inch = 6.895 kPa.
NR = Not Required.
DR = Design Required.
a. Soil classes are in accordance with the Unified Soil Classification System. Refer to Table R401.4.1(2).
b. Table values are based on reinforcing bars with a minimum yield strength of 60,000 psi concrete with a minimum specified compressive strength of 2,500 psi and vertical
reinforcement being located at the centerline of the wall. See Section R404.1.3.3.7.2.
c. Vertical reinforcement with a yield strength of less than 60,000 psi and bars of a different size than specified in the table are permitted in accordance with Section
R404.1.3.3.7.6 and Table R404.1.3.2(9).
d. Deflection criterion is_L_/240, where_L_ is the height of the basement wall in inches.
e. Interpolation is not permitted.
f. Where walls will retain 4 feet or more of unbalanced backfill, they shall be laterally supported at the top and bottom before backfilling.
g. NR indicates vertical wall reinforcement is not required, except for 6-inch-nominal walls formed with stay-in-place forming systems in which case vertical reinforcement shall
be No. 4@48 inches on center.
h. See Section R404.1.3.2 for minimum reinforcement required for basement walls supporting above-grade concrete walls.
i. See Table R608.3 for tolerance from nominal thickness permitted for flat walls.
j. DR means design is required in accordance with the applicable building code, or in the absence of a code, in accordance with ACI 318.
k.
CPC § 0.228 Medium relevance — show source text
657|0.228|0.096|0.025| |19.77|2.750|0.699|0.243|0.102|0.026| |20.48|2.925|0.744|0.258|0.109|0.028| |21.19|3.106|0.790|0.274|0.115|0.030| |24.72|4.074|1.034|0.358|0.151|0.039| |28.25|–|1.307|0.452|0.190|0.049| |31.78|–|1.608|0.556|0.234|0.060| |35.31|–|1.936|0.669|0.281|0.072| |38.84|–|2.291|0.791|0.332|0.085| |42.37|–|2.672|0.922|0.387|0.099| |45.90|–|3.078|1.062|0.446|0.113| |49.43|–|3.510|1.211|0.508|0.129| |52.97|–|3.969|1.368|0.574|0.146| |56.50|–|4.450|1.534|0.643|0.163| |63.56|–|–|1.890|0.792|0.201| |70.62|–|–|2.278|0.954|0.242| |77.68|–|–|2.699|1.130|0.286| |84.74|–|–|3.151|1.318|0.334| |91.81|–|–|3.634|1.520|0.385| |98.87|–|–|4.148|1.734|0.439| |105.93|–|–|4.691|1.961|0.496| |112.99|–|–|–|2.200|0.556|

For SI units: 1 standard cubic foot per minute = 28.32 SLPM, 1 inch = 25 mm, 1 foot = 304.8 mm, 1 inch of mercury = 3.386 kPa Notes: 1 Based on the pressure of 14.7 psig (101 kPa) at 68°F (20°C). 2 Based on the pressure of 19 inches of mercury gauge vacuum (64 kPa) at 68°F (20°C).

1323.3 Location of Piping. Piping risers shall be permitted to be installed in pipe shafts if protected from physical damage, effects of excessive heat, corrosion, or contact with oil. [NFPA 99:5.1.10.11.3.1] 1323.3.1 Prohibited Locations. Piping shall not be installed in kitchens, stairwells, elevator shafts, elevator machine rooms, areas with open flames, electrical service equipment over 600 volts, and areas prohibited Cal- ifornia Electrical Code except for the following locations:

(1) Room locations for medical air compressor supply systems and medical-surgical vacuum pump supply systems

(2) Room locations for secondary distribution circuit panels and breakers having a maximum voltage rating of 600 volts [NFPA 99:5.1.10.11.3.2] **1323.3.2 Approved Locations.

CPC § 1.6 Medium relevance — show source text

PLUMBING APPLIANCES, APPURTENANCES, OR FIXTURES	MINIMUM SIZE TRAP AND TRAP ARM7 (inches)	PRIVATE	PUBLIC	ASSEMBLY8
Water Closet, greater than 1.6 GPF Gravity Tank6	3	4.0	6.0	8.0
Water Closet, greater than 1.6 GPF Flushometer Valve6	3	4.0	6.0	8.0

For SI units: 1 inch = 25 mm

Notes: 1 Indirect waste receptors shall be sized based on the total drainage capacity of the fixtures that drain thereinto, in accordance with Table 702.2. 2 Provide a 2 inch (50 mm) minimum drain. 3 For refrigerators, coffee urns, water stations, and similar low demands. 4 For commercial sinks, dishwashers, and similar moderate or heavy demands. 5 Buildings having a clothes-washing area with clothes washers in a battery of three or more clothes washers shall be rated at 6 fixture units each for purposes of sizing common horizontal and vertical drainage piping. 6 Water closets shall be computed as 6 fixture units where determining septic tank sizes based on Appendix H of this code. 7 Trap sizes shall not be increased to the point where the fixture discharge is capable of being inadequate to maintain their self-scouring properties. 8 Assembly [Public Use (see Table 422.1)]. 9 For a bathtub to shower retrofit, a 1 1 / 2 inch (40 mm) trap and trap arm shall be permitted with a maximum shower size of 36 inches (914 mm) in width and 60 inches (1524 mm) in length. See Section 408.6 and Section 408.7. 10 For drainage fixture unit values related to lots within mobilehome parks in all parts of the State of California, see California Code of Regulations, Title 25, Division 1, Chapter 2, Article 5, Section 1268. For drainage fixture unit values related to lots within special occupancy parks in all parts of the State of Cal- ifornia, see California Code of Regulations, Title 25, Division 1, Chapter 2.2, Article 5, Section 2268.

required, and the unit equivalent of fixtures and devices not shown in Table 702.1 shall be based on the size of trap or trap

arm.

Maximum drainage fixture units for a fixture trap and trap arm loadings for sizes up to 4 inches (100 mm) shall be in accordance with Table 702.1(1).

TABLE 702.1(1) MAXIMUM DRAINAGE FIXTURE UNITS FOR A

TRAP AND TRAP ARM*

SIZE OF TRAP AND TRAP ARM (inches)	DRAINAGE FIXTURE UNIT VALUES (DFU)
11⁄4	1 unit
11⁄2	3 units
2	4 units
3	6 units
4	8 units

For SI Units: 1 inch = 25 mm

*** Exception:** On self-service laundries.

702.2 Intermittent Flow. Drainage fixture units for intermittent flow into the drainage system shall be computed on the rated discharge capacity in gallons per minute (gpm) (L/s) in accordance with Table 702.2.

TABLE 702.1(1) MAXIMUM DRAINAGE FIXTURE UNITS FOR A

TRAP AND TRAP ARM*

CPC § 3.6.2 Medium relevance — show source text
where:

P t = Pressure used in applying Tables R309.3.6.2 (4) through R309.3.6.2 (9). P sup = Pressure available from the water supply source. PL svc = Pressure loss in the water service pipe. [Table R309.3.6.2 (1)] PL m = Pressure loss in the water meter. [Table R309.3.6.2 (2)]

3-52 2025 CALIFORNIA RESIDENTIAL CODE

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

BUILDING PLANNING

PL d = Pressure loss from devices other than the water meter. PL e = Pressure loss associated with changes in elevation. [Table R309.3.6.2 (3)] P sp = Maximum pressure required by a sprinkler. R309.3.6.2.2 Calculation procedure. Determination of the required size for water distribution piping shall be in accordance with the following procedure: Step 1—Determine P sup Obtain the static supply pressure that will be available from the water main from the water purveyor, or for an individual source, the available supply pressure shall be in accordance with Section R309.3.5.1.

Step 2—Determine PL svc

Use Table R309.3.6.2 (1) to determine the pressure loss in the water service pipe based on the selected size of the water service.

Step 3—Determine PL m

Use Table R309.3.6.2 (2) to determine the pressure loss from the water meter, based on the selected water meter size.

Step 4—Determine PL d

Determine the pressure loss from devices other than the water meter installed in the piping system supplying sprinklers, such as pressure-reducing valves, backflow preventers, water softeners or water filters. Device pressure losses shall be based on the device manufacturer’s specifications. The flow rate used to determine pressure loss shall be the rate from Section R309.3.4.2, except that 5 gpm (0.3 L/s) shall be added where the device is installed in a water service pipe that supplies more than one dwelling. As an alternative to deducting pressure loss for a device, an automatic bypass valve shall be installed to divert flow around the device when a sprinkler activates.

Step 5—Determine PL e

Use Table R309.3.6.2 (3) to determine the pressure loss associated with changes in elevation. The elevation used in applying the table shall be the difference between the elevation where the water source pressure was measured and the elevation of the highest sprinkler. Step 6—Determine P sp Determine the maximum pressure required by any individual sprinkler based on the flow rate from Section R309.3.4.1 . The required pressure is provided in the sprinkler manufacturer’s published data for the specific sprinkler model based on the selected flow rate.

Step 7—Calculate P t
CPC § 110.2. Medium relevance — show source text
CODES, CALIFORNIA HISTORICAL BUILDING CODE is the California Historical Building Code, California Code of Regulations, Title 24, Part 8 and Part 2 (Chapter 34).

CODES, CBC is the 2025 California Building Code.

CODES, CEC is the 2025 California Electrical Code.

CODES, CFC is the 2025 California Fire Code.

CODES, CMC is the 2025 California Mechanical Code.

CODES, CPC is the 2025 California Plumbing Code.

COEFFICIENT OF PERFORMANCE (COP), COOLING is the ratio of the rate of net heat removal to the rate of total energy input, calculated under designated operating conditions and expressed in consistent units, as determined using the applicable test method in the Appliance Efficiency Regulations or Section 110.2.

COEFFICIENT OF PERFORMANCE (COP), HEATING is the ratio of the rate of net heat output to the rate of total energy input, calculated under designated operating conditions and expressed in consistent units, as determined using the applicable test method in the Appliance Efficiency Regulations or Section 110.2.

COEFFICIENT OF PERFORMANCE (COP), HEAT PUMP is the ratio of the rate of useful heat output delivered by the complete heat pump unit (exclusive of supplementary heating) to the corresponding rate of energy input, in consistent units and as determined using the applicable test method in Appliance Efficiency Regulations or Section 110.2.

COMBINED ENERGY EFFICIENCY RATIO (CEER) is the ratio of net cooling capacity (in Btu/hr) to total rate of electrical energy input (in watts) of a cooling system under designated operating conditions, including standby mode, as determined using the applicable test method in the Appliance Efficiency Regulations.

COMBUSTION AIR POSITIVE SHUT-OFF is a means of restricting air flow through a boiler combustion chamber during standby periods, used to reduce standby heat loss. A flue damper and a vent damper are two examples of combustion air positive shut-off devices.

COMBUSTION EFFICIENCY is a measure of the percentage of heat from the combustion of gas or oil that is transferred to the medium being heated or lost as jacket loss.

COMMERCIAL BOILER is a type of boiler with a capacity (rated maximum input) of 300,000 Btus per hour (Btu/h) or more and serving a space heating or water heating load in a commercial building.

COMMISSION is the California State Energy Resources Conservation and Development Commission, which is also referred to as the California Energy Commission.

COMPARTMENTALIZATION is when a dwelling unit enclosure area, including walls, ceilings, and floors shared with exterior spaces or adjacent spaces in the building, including but not limited to neighboring units, corridors, and elevator shafts, is constructed to prevent air leakage.

10 2025 CALIFORNIA ENERGY CODE

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

ALL OCCUPANCIES—GENERAL PROVISIONS

Frequently asked questions

How do I get device ΔP when manufacturer data is missing?

If manufacturer ΔP is not available, § 610.2 requires the device inlet/outlet diameter be at least the distribution pipe diameter so you don't create an uncontrolled restriction; alternatively, use a conservative replacement device with known performance or seek AHJ approval for engineering assumptions.

Where do I find friction‑loss values to size pipe?

Use the “Fairly Rough” or “Rough” charts in Appendix A as directed by § 610.6; these charts give head loss per 100 ft for a given flow and pipe material.

What if my calculated velocity slightly exceeds the code limit?

If a sizing based on prescriptive tables causes v > limit, you must increase pipe size (or submit engineering design acceptable to the AHJ under § 610.13(1)). You may not rely on exceeding the velocity limits without AHJ‑accepted engineered justification.

Can I bypass a device (e.g., softener) for sprinkler demand?

Where a device's ΔP would reduce sprinkler performance, the residential rules (and similar provisions in the code) allow an automatic bypass for sprinkler activation as an alternative to deducting device ΔP — follow the specific sizing and local AHJ rules (see practice described in sizing procedures referenced in the code).

Are copper velocity limits different for hot and cold?

Yes: for copper systems cold water is limited to 8 ft/s and hot water to 5 ft/s per § 610.12. Check both hot and cold branches where applicable.

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Related in the CPC

How do I size the water service, meter, and building supply piping?

How are fixture units and branch sizing handled (including flushometer fixtures)?

Sizing, Pressure and Flow Calculations

California Plumbing Code