Water Supply · Definition
What Is a Private Fire Service Main (NFPA 24)?
Reviewed by a licensed Professional Engineer · NY, NJ, PA, MD, DE · Last reviewed · Code basis: NFPA 24 (2022); NFPA 13 (2022); 2021 IFC Section 507; NYS 2025 Uniform Code; NYC 2022 Construction Codes; NJ UCC 2024 I-Codes; PA UCC 2021 I-Codes; MD 2021 IBC and NFPA 1 (2024); DE Regulation 701 (2026)
General guidance, not a code determination for any project. Confirm the adopted code and local amendments with the authority having jurisdiction.
A private fire service main is the owner-owned underground piping that carries water from the public water main, or from a private source such as a tank or pond, to a property’s fire protection systems: the sprinkler and standpipe risers, the private fire hydrants and the fire department connections. The standard that governs how that piping is designed, installed and tested is NFPA 24, the Standard for the Installation of Private Fire Service Mains and Their Appurtenances. The public utility’s responsibility ends at the tap or the meter; everything downstream on the private side, up to the base of each riser, is the private fire service main.
Owners meet the term on a site plan long before they meet it in a code book. The civil engineer draws the main, the water purveyor approves the tap, the sprinkler contractor often installs the last run into the building, and the fire marshal witnesses the test. This article defines the private fire service main, lists its parts, explains where NFPA 24 picks up from the water purveyor’s rules and hands off to NFPA 13, and separates it from the terms it is confused with.
At a Glance: Private Fire Service Main
- Definition: privately owned underground pipe and fittings, with their valves, hydrants and fire department connections, that supply water for fire protection from a source to the base of each system riser, private hydrant and hose connection on the property.
- Governing code and section: NFPA 24 (2022 edition), Chapter 1 for scope and Chapter 3 for definitions; Chapter 10 for underground pipe, depth of cover, restraint, flushing and hydrostatic testing. The International Fire Code (IFC), 2021 edition, Section 507 sets the fire flow and hydrant requirements the main has to deliver. State and city adoptions reference different NFPA 24 editions; see the jurisdiction table.
- Who it applies to: the property owner, who owns and maintains the main; the civil or fire protection engineer who designs it; the underground contractor who installs it; the water purveyor who controls the tap; and the fire code official who approves it.
- When it is required: whenever a sprinkler system, standpipe, private hydrant or fire pump on the site needs water that the public main at the street cannot deliver directly to the riser, which in practice means every sprinklered building that is not fed by a single short service at the property line.
- Typical output: a civil site utility plan showing pipe size, material, depth, valves, hydrants and restraint; hydraulic calculations tied to a hydrant flow test; and the Contractor’s Material and Test Certificate for Underground Piping signed after flushing and a 2 hour hydrostatic test.
- Often confused with: the public water main, the domestic water service, the fire service lateral or lead-in, and the aboveground sprinkler piping that NFPA 13 governs.
What a Private Fire Service Main Includes
A private fire service main is a system, not a single pipe. NFPA 24 (2022) covers everything from the connection at the water source to the point where the pipe rises out of the ground at the building, and it lists the appurtenances that ride on that pipe. The table names each component, what it does and the NFPA 24 chapter that governs it, so that an owner reading a civil set can match the drawing to the standard.
| Component | What it does | NFPA 24 (2022) basis |
|---|---|---|
| Underground pipe | Ductile iron, PVC (American Water Works Association, AWWA, C900) or other listed pipe, sized by hydraulic calculation, usually 6 in. or 8 in. on a looped site, and buried below the local frost depth | Chapter 10, pipe materials and depth of cover |
| Fittings and joints | Mechanical joint, push-on or flanged fittings that turn, tee and reduce the main | Chapter 10 |
| Thrust blocks or restrained joints | Concrete bearing blocks or mechanical joint restraints that keep pressure from pushing fittings apart at every bend, tee, plug and hydrant branch | Chapter 10, restraint |
| Control valves and indicator posts | Listed gate or butterfly valves, operated through a post indicator valve (PIV) or a valve box, that isolate the main or a section of it | Chapter 6, valves |
| Check valves and backflow preventers | Keep system water out of the public supply; the purveyor’s cross-connection rules decide whether a double check or a reduced pressure assembly is required | Chapter 6, with the purveyor’s cross-connection program and NFPA 13 (2022) Chapter 16 |
| Private fire hydrants | Hydrants on the owner’s main that give the fire department a water source within the hose lay distance the fire code sets | Chapter 7, hydrants; 2021 IFC Section 507.5 |
| Fire department connection (FDC) piping | The underground or aboveground pipe from the FDC inlet to the system side of the riser, with its check valve and drain | Chapter 5, water supplies (fire department connections); 2021 IFC Section 912 |
| Lead-ins | The last run from the loop or the main to the base of each riser, including the 90 degree bend up through the slab and the flange where NFPA 13 piping begins | Chapter 10; the handoff point to NFPA 13 (2022) Chapter 6 |
Two components on the table are not fire protection parts at all, yet they decide the hydraulics. The backflow preventer can cost 5 to 12 psi of pressure at system demand, and the meter, where the purveyor requires one on a fire service, adds its own loss. Both have to appear in the hydraulic calculation, and both are the reason the fire protection engineer and the civil engineer need to agree on the vault layout before the tap is ordered.
Figure 1: A Private Fire Service Main on a Site Plan
Where the Code Defines a Private Fire Service Main
NFPA 24 (2022) Chapter 1 sets the scope: the standard applies to private fire service mains and their appurtenances supplying automatic sprinkler systems, standpipes, private hydrants, monitor nozzles, hose houses and fire pump suction and discharge piping that runs underground. Chapter 3 carries the definition, which in plain terms is pipe and appurtenances on private property, between a water source and the base of the system riser or the hydrant, that is dedicated to or shared with fire protection. The standard does not cover the public main in the street, and it does not cover the piping inside the building above the riser flange.
The water purveyor’s rules govern the upstream end. Whether a fire service may be unmetered, whether a detector check or a full backflow assembly is required, where the tap and curb valve sit, and how the service is sized at the street are decided by the utility, such as New York City Department of Environmental Protection, New Jersey American Water or the Washington Suburban Sanitary Commission in Maryland. The plumbing code adopted by the jurisdiction governs backflow protection on the domestic side, and most purveyors apply a parallel cross-connection program to fire services.
NFPA 13 (2022) governs the downstream end. Chapter 5 covers water supplies and requires the supply to meet the sprinkler demand plus hose allowance at the base of the riser, and Chapter 6, on underground piping, points the designer to NFPA 24 for the pipe outside the building and defines where the two standards meet. NFPA 13 (2022) Chapter 6 carries the underground Contractor’s Material and Test Certificate and requires the underground piping to be flushed before it is connected to the sprinkler piping, so in practice the private fire main is flushed and tested before the aboveground system is accepted. DGA’s plain-English guide to what NFPA 13 covers and where it stops explains that boundary from the sprinkler side, and the article on what a sealed sprinkler shop drawing set includes shows where the underground information has to appear on the sprinkler drawings.
The fire code sets the performance target. The 2021 IFC Section 507 requires an approved water supply capable of delivering the required fire flow, calculated under Appendix B where the jurisdiction adopts that appendix, or by another approved method, from construction type, floor area and sprinkler status, and requires hydrants where a building is more than a set distance from a public hydrant, with 400 ft the general limit and 600 ft permitted for sprinklered buildings (Section 507.5.1). NFPA 24 tells the designer how to build the main; IFC 507 tells the designer how much water it has to deliver and where the hydrants go.
How Each Jurisdiction Adopts NFPA 24 and Reviews the Underground
Every state DGA works in requires NFPA 24 through its building and fire codes, but the edition, the reviewer and the filing name differ. The table lists the adopted code, the NFPA 24 edition referenced by that code, who reviews the underground piping and what the submission is called. Model codes reference NFPA 24 by edition, so the edition in force is set by the code the jurisdiction adopted, not by the newest NFPA printing.
| Jurisdiction | Adopted code and NFPA 24 edition | Who reviews the underground | Filing name |
|---|---|---|---|
| New York State (outside NYC) | 2025 Uniform Code based on the 2024 I-Codes; 2024 IBC and IFC reference NFPA 24 (2022) | Local code enforcement official; local water or sewer authority for the tap | Building permit with site utility plan; water service application to the purveyor |
| New York City | 2022 Construction Codes and 2022 Fire Code; NFPA 24 as modified by Building Code Chapter 35 and Appendix Q, earlier edition than 2022 | Department of Buildings (sprinkler and standpipe plan review); Department of Environmental Protection for the tap and site connection; FDNY for hydrants and FDC placement | DOB NOW sprinkler (SP) or standpipe (SD) work type; DEP Site Connection Proposal and tap permit |
| New Jersey | Uniform Construction Code, 2024 I-Codes (New Jersey editions), effective August 17, 2026; 2024 IBC references NFPA 24 (2022). Uniform Fire Code on a 2018 IFC basis for existing buildings | Municipal fire protection subcode official; water purveyor such as New Jersey American Water for the tap and backflow | UCC construction permit, fire protection subcode technical section; purveyor fire service application |
| Pennsylvania | Uniform Construction Code, 2021 I-Codes, effective January 1, 2026; 2021 IBC references NFPA 24 (2019). No statewide fire code outside the UCC | Municipal or third-party code official under the UCC; the municipal water authority for the tap; Philadelphia Water Department and Licenses and Inspections (L&I) inside Philadelphia | UCC building permit with fire protection plans; authority service connection application |
| Maryland | Building Performance Standards, 2021 IBC, referencing NFPA 24 (2019); State Fire Prevention Code, NFPA 1 (2024), which references NFPA 24 (2022) | County building official and fire marshal; Washington Suburban Sanitary Commission (WSSC Water) in Montgomery and Prince George’s counties, or the county utility elsewhere, for the fire service connection | County building and fire protection permits; WSSC site utility plan approval and fire service application |
| Delaware | State Fire Prevention Regulations, Regulation 701 (2026), NFPA 1 (2024) and NFPA 13 (2025); NFPA 24 edition set by Regulation 701. IBC 2021 in New Castle and Sussex, 2018 in Kent and Wilmington | Office of the State Fire Marshal, Technical Services Division, plan review before the county permit; Wilmington Fire Marshal inside the city; the water utility for the tap | State Fire Marshal plan review application for underground fire mains and hydrants; county building permit |
Editions as listed in DGA’s Fire Code Cheat Sheet for NY, NJ, PA, MD and DE. Local amendments and purveyor standards are not shown.
DGA designs private fire service mains, hydrant layouts and the sprinkler and fire pump systems they feed across New York, New Jersey, Pennsylvania, Maryland and Delaware. Project briefs get confirmation and preliminary code feedback within one business day. See where DGA works →
Private Fire Service Main vs the Terms It Is Confused With
Four other pipes carry water onto or through a sprinklered property, and each has a different owner, standard and reviewer. The table sets them side by side. The ownership column matters most: the owner maintains, tests and repairs whatever is on the private side, and NFPA 25 inspection obligations follow the same line.
| Term | What it is | Who owns it | Governing standard | Where it ends |
|---|---|---|---|---|
| Public water main | The distribution pipe in the street or utility easement that serves many properties | Water purveyor | AWWA standards and the purveyor’s design rules | At the tap or corporation stop |
| Fire service lateral or lead-in | The single run from the tap to the first valve, vault or riser; “lead-in” also names the last run from a loop into a riser | Owner from the property line or curb valve; purveyor rules vary on the piece under the sidewalk | NFPA 24 on the private side; purveyor standards on the public side | At the base of the riser |
| Private fire service main | All underground fire protection pipe on the property, including loops, laterals, hydrant branches and FDC piping | Owner | NFPA 24 (2022 or the adopted edition) | At the base of each riser, hydrant or hose connection |
| NFPA 13 underground piping | The same pipe, viewed from the sprinkler standard, which refers the designer to NFPA 24 and sets the handoff point at the riser flange | Owner | NFPA 13 (2022) Chapter 6, which invokes NFPA 24 | At the riser flange, where NFPA 13 aboveground rules begin |
| Domestic water service | The potable supply to plumbing fixtures, metered and protected by a backflow preventer | Owner from the curb valve | Adopted plumbing code and purveyor rules | At the water meter and building distribution |
A combined service, where one pipe from the street splits in a vault to a domestic meter and a fire line, is common on small sites and is permitted when the purveyor allows it and the split is upstream of the fire main’s control valve. On that arrangement the shared pipe has to satisfy both the plumbing code and NFPA 24, and the fire protection hydraulic calculation has to include the domestic demand or show that it is isolated during a fire.
Figure 2: What Sits on Each Side of the Property Line
- Distribution main in the street, sized for the district, not for one building
- Tap, corporation stop and curb valve set by the purveyor’s standard details
- Hydrant flow test data, usually from 2 public hydrants, that sets the supply curve
- Service rules: metering, cross-connection control, allowable fire service sizes
- Reviewed by the utility; not covered by NFPA 24
- Backflow preventer or detector check in a vault or heated enclosure
- Underground pipe, 6 in. minimum for a hydrant branch, buried below frost depth
- Thrust blocks or restrained joints at every change of direction
- Control valves with indicator posts, sectional valves on a loop, private hydrants, FDC piping
- Flushed, hydrostatically tested at 200 psi for 2 hours, and certified under NFPA 24 (2022) Chapter 10
How a Private Fire Service Main Is Installed and Accepted
NFPA 24 (2022) Chapter 10 holds the installation rules that show up on inspection. Pipe is buried so that its top is below the local frost line, which in the region DGA serves generally means 3 to 4.5 ft of cover and more under driveways and loading areas where wheel loads govern; the standard sets depth by frost penetration and by cover under traffic, so the civil engineer picks the deeper of the two. Every bend, tee, reducer, plug and hydrant branch is restrained by a thrust block poured against undisturbed soil or by a listed mechanical joint restraint, and the drawings have to show which method is used and where.
Acceptance has three steps that the fire code official or the owner’s engineer witnesses. The main is flushed at a flow high enough to carry out stones and debris, which for a 6 in. main is on the order of 880 gpm and for an 8 in. main about 1,560 gpm, so the contractor has to plan where that water goes.
The main is then hydrostatically tested at 200 psi, or 50 psi above the system working pressure where that exceeds 150 psi, for 2 hours, with any makeup water held within the allowance NFPA 24 (2022) Chapter 10 calculates from pipe length, diameter and test pressure. The installing contractor then signs the Contractor’s Material and Test Certificate for Underground Piping, which records the pipe, the test and the flush, and that certificate becomes part of the sprinkler acceptance file; NFPA 13 (2022) Chapter 6 carries the same certificate form.
Where a fire pump draws from the main, the pump acceptance test is the first time the whole underground is run at full flow. DGA’s account of what happens at a diesel fire pump acceptance test describes how that test exposes a partly closed valve or a sized-down lead-in that the hydrostatic test could not reveal.
When a Private Fire Service Main Is Required
A private fire service main is required whenever the water for a required fire protection system has to travel across private property underground to reach it. That covers every sprinklered building set back from the street, every site with private hydrants under IFC Section 507.5, every standpipe fed from grade, and every fire pump whose suction pipe runs underground. The short exception is a small building at the property line whose riser sits a few feet inside the wall; even then the lead-in from the tap to the riser is a private fire service main, just a short one.
Whether the main also needs a fire pump is a separate question that depends on what the public supply can deliver at the hydrant and what the sprinkler system demands at the riser. DGA’s hydrant flow test calculator turns field static, residual and pitot readings into the available flow at 20 psi, and the article on how engineers decide whether a fire pump is needed explains how that supply curve is compared against demand before the main is sized.
Who Needs to Act
| Who | One action |
|---|---|
| Owner | Confirm in writing where the purveyor’s ownership ends and keep the underground test certificate and as-built with the building records, because NFPA 25 maintenance of valves and hydrants falls on the owner from that line onward. |
| Civil engineer | Order a current hydrant flow test before sizing the main, and show pipe material, depth, restraint method, valves and hydrants on the utility plan with the NFPA 24 edition named. |
| Fire protection engineer | Carry the backflow preventer, meter and underground friction loss into the sprinkler and fire pump calculations, and set the handoff point at the riser flange on both sets of drawings. |
| Sprinkler or underground contractor | Schedule the flush and the 2 hour hydrostatic test with the inspector before backfilling joints, and deliver the signed Contractor’s Material and Test Certificate for Underground Piping. |
| Water purveyor | Approve the tap size, metering and backflow arrangement and issue the flow test or hydraulic model data the design relies on. |
| Fire code official (authority having jurisdiction, AHJ) | Review hydrant spacing, FDC location and PIV placement against the fire code and NFPA 24, and witness or accept the underground test. |
Key Takeaway: A private fire service main is every foot of underground fire protection pipe on the owner’s side of the tap, with its valves, hydrants and FDC piping, from the public main to the base of the riser. NFPA 24 (2022 or the edition the jurisdiction adopted) governs how it is built, restrained, flushed and tested at 200 psi for 2 hours; IFC Section 507 sets how much water it must deliver and where the hydrants go; NFPA 13 takes over at the riser flange. The owner owns it, maintains it and signs for it.
Frequently Asked Questions
Is a private fire service main the same as the water main in the street?
No. The main in the street belongs to the water purveyor and is designed to utility standards. The private fire service main begins at the tap or the property line, belongs to the owner, and is designed, installed and tested under NFPA 24.
Does NFPA 13 or NFPA 24 govern the underground pipe to a sprinkler riser?
NFPA 24 governs the underground pipe, and NFPA 13 (2022) Chapter 6 refers the designer to it. NFPA 13 takes over at the riser flange where the pipe comes out of the ground, and NFPA 13 (2022) Chapter 6 requires the underground piping to be flushed before it is connected to the sprinkler system, with the results on the underground test certificate.
What test does a private fire service main have to pass?
A flush at high flow followed by a hydrostatic test at 200 psi, or 50 psi above the system working pressure where that is higher, held for 2 hours with leakage within the limit NFPA 24 (2022) Chapter 10 sets. The contractor records both on the Contractor’s Material and Test Certificate for Underground Piping.
Who maintains private fire hydrants and the valves on a private fire main?
The owner. Everything on the private side of the tap, including hydrants, post indicator valves, sectional valves and backflow preventers, is the owner’s to inspect, test and maintain under NFPA 25, and the purveyor will not service it.
Does every sprinklered building need a private fire service main?
Conditional: every sprinklered building has at least a short one, because the pipe from the tap to the riser is a private fire service main by definition. A full looped main with sectional valves and private hydrants is needed when the building is set back from the street, when IFC Section 507.5 hydrant spacing cannot be met from public hydrants, or when a fire pump or standpipe is fed underground.
More in Water Supply
- Do You Need a Fire Pump? How Engineers Decide (NFPA 20)
- Water Supply for Fire Protection: The Complete Guide
- What Is a Fire Pump Controller and Transfer Switch?
- When Can a Well or Private Source Supply Fire Protection?
- What Is Backflow Preventer Pressure Loss in Sprinkler Calcs?
- Split-Case vs In-Line vs Vertical Turbine: Which Fire Pump?
This article is general information, not a substitute for a project-specific design or code analysis. Code editions, local amendments, purveyor standards and reviewer practice change; confirm the adopted code and the authority having jurisdiction for the project.
Sizing a Fire Service Main or Hydrant Loop?
Send the site plan, the hydrant flow test and the jurisdiction. DGA sizes the private fire service main, sets the hydrant and FDC layout and coordinates the tap with the purveyor so the underground passes review the first time. Project briefs get confirmation and preliminary code feedback within one business day.