NFPA 22: Water Tank Requirements for Fire Protection

What Is NFPA 22?

NFPA 22, Standard for Water Tanks for Private Fire Protection, sets the minimum requirements for the design, construction, installation, and maintenance of water storage tanks that supply water for private fire suppression systems. This includes sprinkler systems, standpipes, and private hydrants when the municipal water supply is inadequate in flow, pressure, or reliability.

The standard has been in continuous development since 1909, when the NFPA Committee on Gravity Tanks produced its first edition. The 2023 edition — the current version — was issued by the Standards Council on April 14, 2022, and supersedes all previous editions.

NFPA 22 is a design and installation standard. Once a tank is built and placed in service, all ongoing inspection, testing, and maintenance falls under NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. Both standards apply to the same tank — they are complementary, not interchangeable.

Scope and Tank Types Covered

Section 1.1 defines the scope: NFPA 22 covers the design, construction, installation, and maintenance of tanks that supply water for private fire protection, including gravity tanks, suction tanks, pressure tanks, and embankment-supported coated fabric suction tanks — along with their towers, foundations, pipe connections, valve enclosures, filling systems, and freeze protection.

Six Tank Configurations (2023 Edition)

Chapter	Tank Type	Standard Capacity Range	Notes
Ch. 5	Welded carbon steel gravity / suction tanks	5,000–500,000 gal	Most common for large commercial/industrial; must comply with AWWA D100 or D107
Ch. 6	Factory-coated bolted carbon steel tanks	4,000–500,000 gal	Cylindrical; factory coating per AWWA D103; field bolted assembly
Ch. 7	Pressure tanks	AHJ-approved capacity	Air/gas pressure expels water; limited to specific NFPA systems; ASME BPV Code construction
Ch. 8	Wood gravity / suction tanks	5,000–100,000 gal	Redwood, cedar, Douglas fir; HT-stamped; common on older elevated tank installations
Ch. 9	Embankment-supported coated fabric suction tanks	100,000–1,000,000 gal	Nylon fabric with elastomer coating; large rural/industrial applications
Ch. 11	Fiberglass-reinforced plastic (FRP) tanks	2,000–50,000 gal typical	Added in 2008 edition; AWWA D120 or D121; atmospheric pressure only

Sizing Requirements — Chapter 4

NFPA 22 does not prescribe fixed minimum tank sizes. Section 4.1.1 states that tank capacity and elevation must be determined by the required fire flow rate, flow duration, and pressures required by the attached fire protection system. This means sizing is always system-specific and must be engineered to the actual hydraulic demand.

Key sizing rules from Chapter 4:

• Net capacity for suction tanks: the volume between the overflow inlet and the anti-vortex plate (§4.1.4). For all other tanks: between the overflow inlet and the discharge outlet (§4.1.5).
• 8-hour fill requirement: The water supply must be capable of refilling the minimum required fire protection volume within 8 hours (§4.2.1.4).
• Water level maintenance: Tank water level must never be more than 4 inches below the designated fire service level (§14.4.3).
• 2023 update — pump suction pressure: The 2023 edition explicitly requires that pump suction pressure (NPSH) be factored into tank sizing when a fire pump draws from the tank. Annex A.4.1.6 references NFPA 20 for net positive suction head requirements.

Approved Materials — Section 4.4

Section 4.4.1 limits tank materials to five categories: steel, wood, concrete, coated fabrics, and fiberglass-reinforced plastic. Each material type has its own chapter with detailed fabrication, corrosion protection, and structural requirements. Elevated wood and steel tanks must be supported on steel towers or reinforced concrete towers (§4.4.2).

Compliant vs. Equivalent Tanks

A tank is NFPA 22 compliant when it matches a tank type explicitly covered by one of the six chapters above. A tank is NFPA 22 equivalent when it meets or exceeds the performance requirements of the standard through an alternative design — Section 1.4 allows equivalency, but requires technical documentation submitted to the AHJ for approval. This distinction matters for corrugated bolted steel tanks and other designs not explicitly covered in a dedicated chapter.

Location Requirements — Section 4.3

Tanks must be located to minimize fire exposure to the tank structure itself. Specific requirements from §4.3:

• Steelwork within 20 feet of combustible buildings, windows, or door openings must be fireproofed or protected by open sprinklers (§4.3.1.2).
• Fireproofing must have a fire resistance rating of at least 2 hours (§4.3.2).
• Foundations must provide adequate support and anchorage for the tower (§4.3.3).
• If the tank or supporting structure sits on a building, that building must be designed to carry the maximum loads (§4.3.4).

Pipe Connections and Fittings — Chapter 14

Chapter 14 is the most detailed operational chapter in NFPA 22 and the section most relevant to anyone connecting a fire water tank to a suppression system. Key requirements:

Discharge Pipe (§14.2)

• Minimum discharge pipe size: 6 inches (§14.2.2).
• Steel pipe in contact with storage water: 2–5 inch pipe must be Schedule 80; 6 inch and larger must be Schedule 40 (§14.1.12.2).
• A listed check valve must be installed horizontally in the discharge pipe (§14.2.11).
• A listed indicating control valve must be installed on each side of the check valve (§14.2.12.2).
• Where the tank serves as a suction source for a fire pump, the indicating valve must be an OS&Y (outside screw and yoke) type (§14.2.12.6).

Anti-Vortex Plate — Required for Every Suction Tank (§14.2.13)

Every suction tank discharge outlet must have an anti-vortex plate assembly. This is a horizontal steel plate at least twice the diameter of the outlet pipe, mounted at the outlet at a height above the tank bottom equal to one-half the diameter of the discharge pipe (minimum 6 inches). The plate prevents air from entering the pump suction line as water level drops.

Fill Line Separation (2023 Update)

One of the notable 2023 edition changes: Section 14.4.10.1 now specifies that the fill line discharge point must be located at least 10 pipe diameters (measured on the fill pipe diameter) from the suction pipe centerline. This separation prevents fill-line turbulence from introducing air into the pump suction during simultaneous filling and fire pump operation, which can cause cavitation.

Water Level Monitoring (§14.1.8 and §14.9)

All tanks must have a water level gauge of suitable design. NFPA 72 supervision must be provided for:

• Water temperature below 40°F (return alarm at 40°F)
• Water level drop of 12 inches below normal (3 inches for pressure tanks)
• Return of water level to normal
• For pressure tanks: pressure 10 PSI below or above normal

Overflow, Drain, and Venting

Three critical passive systems that are frequently underspecified in field installations:

Overflow Pipe (§14.6)

The overflow pipe must have greater capacity than the fill connection — never less than 3 inches throughout. The inlet must sit at the top capacity line or high waterline, never closer than 2 inches from the top of the tank. Where the fill capacity is unknown, the overflow pipe must be at least one pipe size larger than the fill line.

Roof Vent (§4.15)

Where the steel roof is essentially airtight, a substantial vent above the maximum water level is required. Vent pipe cross-sectional area must equal at least one-half the area of the discharge or fill pipe (whichever is larger). A corrosion-resistant screen with 3/8-inch holes must be provided to exclude animals, with a net area at least equal to the vent line — and gross area at least 1.5× the discharge pipe area.

Freeze Protection — Chapters 15 and 16

Any tank subject to freezing must be heated (§16.1.1). The standard requires that the temperature of the coldest water in the tank be maintained at or above 42°F (5.6°C) during the coldest weather (§16.1.2). A low water temperature alarm set at 40°F is mandatory.

Frostproof Casing (§15.2)

A listed frostproof casing must be placed around all exposed tank piping in localities where the lowest mean one-day atmospheric temperature is 20°F or lower. Table 15.1.2.4 specifies minimum insulation thickness by material type and design temperature — ranging from 1 inch of polystyrene at +15°F to 2.5 inches at -40°F.

Heating Systems (§16.3)

NFPA 22 permits six heating methods, with requirements depending on the lowest one-day mean temperature at the site and the tank type. Tables 16.2.1(a), (b), and (c) define which systems are permitted for each scenario:

Heating Method	How It Works	Typical Application
Gravity circulating (steam)	Hot water rises from heater into tank; cold water returns by gravity	Most common for elevated steel tanks
Steam-heated vertical radiator	Radiator immersed in tank; required for towers over 100 ft	Tall elevated tanks
Immersed steam coils	Copper or brass coil inside tank heated by steam	On-grade suction tanks
Electric immersion heaters	Listed immersion element; tank must stay full; low-water cutoff required	All tank types where electricity is available
Gas or oil-fired water heaters	Listed heater with high-limit switch at 190°F	Remote locations with gas supply
Water recirculating with heat exchanger	Thermostat-activated pump circulates water through external heat exchanger	Embankment-supported fabric tanks below 5°F

The heater capacity must be calculated using the heat loss formula in Figure 16.1.4, which accounts for tank surface area, insulation R-value, the temperature differential between desired water temperature and outside ambient, and a wind exposure factor of up to 15% additional load.

Acceptance Testing — Chapter 17

Before a tank is placed in service, a joint inspection by the tank contractor and owner's representative must be conducted, with the AHJ notified. Written reports must be made in triplicate and signed by contractors and owners (§17.1.2).

Test Requirements by Tank Type

Tank Type	Required Test	Pass Criterion
Welded steel	Fill with water to maximum working level; inspect all welds	No leaks in shell, bottom, or roof
Bolted steel	Fill with water; repair per AWWA D103	No detectable leaks
Pressure tanks	ASME hydrostatic test (min. 150 PSI); operating test at working pressure	No more than 0.5 PSI drop in 24 hours at working pressure
Concrete	Fill; stand 24 hrs; measure drop over 72 hrs	No measurable leakage after placing in service
Wood	Fill; test liquid tightness 48 hrs with qualified wood tank specialist	Liquid tight per NWTI Bulletin S82
FRP	Hydrostatic fill test; water must stabilize within 2 hours	No visible leakage; stable water level
All suction tanks	Anti-vortex plate inspection before filling	Plate dimensions, long-radius elbow, and height per §14.2.13.2

NFPA 22 vs. NFPA 25 — Design vs. Maintenance

Chapter 18 of NFPA 22 consists of a single sentence: "Tanks shall be periodically inspected, tested, and maintained in accordance with NFPA 25." This is intentional — NFPA 22 governs the tank as built; NFPA 25 governs the tank in service.

Standard	Scope	When It Applies
NFPA 22	Design, construction, installation	Design phase through acceptance testing
NFPA 25	Inspection, testing, maintenance	Entire service life after placement in service

Key NFPA 25 Inspection Frequencies for Water Tanks

• Monthly: Visual water level check (if no alarm system is used)
• Quarterly: Visual water level check (even when alarm system is present); heating system operation; water temperature verification
• Annual: Full visual inspection of tank exterior, supports, cathodic protection, vents, and overflow; heating system annual inspection
• Every 3 years: Internal inspection for steel tanks without interior coating or cathodic protection
• Every 5 years: Internal inspection for steel tanks with interior protective coating

What Changed in the 2023 Edition

The 2023 edition introduced several substantive changes from the 2018 edition:

• Pump suction pressure: Tank sizing requirements updated to explicitly require consideration of fire pump net positive suction head (NPSH) in accordance with NFPA 20 (§4.1.6, Annex A.4.1.6).
• Fill line and suction pipe separation: New 10-pipe-diameter minimum separation distance between fill line discharge and suction pipe centerline to prevent cavitation (§14.4.10.1.2).
• External load requirements: Wind, snow, and live load sections updated to reference current ASCE 7 and local building code requirements, replacing outdated prescriptive values.
• Electric immersion heater criteria: Chapter 16 added new requirements for electric immersion heaters, including mandatory low-water cutoff switches and continuous immersion requirements.
• Lowest one-day mean temperature map removed: The prescriptive temperature map was removed; designers must now use calculation-based methods to determine heating needs.
• Valve requirements: Additional valve requirements added to improve system maintainability without impairing fire protection.
• Redundant sections removed: Editorial cleanup reduced duplicate requirements, particularly in Chapters 5 and 6 where AWWA D100 and D103 references were consolidated.

When Is NFPA 22 Required?

Four scenarios typically trigger NFPA 22 compliance requirements:

1. New construction where the municipal water supply is inadequate in flow, pressure, or reliability for the building's fire suppression system demand.
2. Major renovations where an upgraded fire protection system requires a new or upgraded private water supply.
3. Change in use or occupancy that increases fire hazard classification and triggers higher fire flow requirements.
4. Insurance or AHJ mandate — many insurers and fire marshals require NFPA 22-certified tanks as a condition of policy approval or occupancy permits regardless of municipal supply adequacy.