Acceptance testing is when a sprinkler system proves it works in reality rather than on the drawings. The values measured at this stage become the reference point for decades of inspection and testing. The system acceptance part of NFPA 13 defines which tests are carried out, the criteria they must meet and the documents handed over.
What this part of the standard covers
- Flushing and testing the underground supply (together with NFPA 24)
- Hydrostatic testing of aboveground piping
- Air tests, trip tests and water delivery time for dry and pre-action systems
- Waterflow alarms, supervisory signals and main drain tests
- Backflow preventer, pressure-reducing valve and pump tests
- Acceptance documents, signs and what the owner receives
Key test criteria
| Test | General criterion |
|---|---|
| Hydrostatic test | 13.8 bar (200 psi) for 2 hours; where maximum working pressure exceeds 10.3 bar (150 psi), 3.4 bar (50 psi) above maximum working pressure |
| Hydrostatic acceptance | No visible leakage on aboveground pipe; pressure read at the lowest point of the system or section under test |
| Dry system air test | 2.8 bar (40 psi) air for 24 hours; loss not more than 0.1 bar (1.5 psi) |
| Underground flushing | Before connection to aboveground piping, at a flow able to carry debris out |
| Test water | No leak sealants or corrosive additives |
In winter, hydrostatic test water can freeze; after testing a dry system, make sure the pipework is fully drained. For freezing risk see winterizing sprinkler systems.
The logic of the tests
Flushing comes first
Stones, soil and weld debris left in the underground main are carried to sprinklers and alarm valves the first time water enters the system. So the underground is flushed at adequate flow before it is connected to aboveground piping. Keeping aboveground pipe clean during installation, and flushing it when needed, is the cheapest and most effective step in commissioning; see commissioning mistakes.
Hydrostatic test: tightness and strength
The hydrostatic test shows the system can withstand pressure above normal working pressure and that joints do not leak. It can be run with or without sprinklers fitted, but sensitive equipment (some alarm devices, pressure switches) must be protected. Reading test pressure at the lowest point means upper floors in tall buildings see less; that is part of the test's logic.
Dry and pre-action systems
Dry systems also get a 24-hour air test, to stop small leaks from running the compressor constantly and tripping the valve unintentionally. The dry pipe valve is then full-trip tested and the water delivery time is measured at the remote test connection. On pre-action systems, the detection system and the valve are proven to work together; see pre-action sprinkler systems.
Alarms and supervision
Flow through the inspector's test connection proves the waterflow alarm locally and at the monitoring centre. Closing control valves proves the supervisory signals. It is not enough for the alarm to appear on the panel; check that the signal reaches its destination.
Main drain test: the baseline
The main drain test at acceptance records static and residual pressure. These values are the reference for NFPA 25 periodic tests to spot deterioration of the supply or a partly closed valve. Without the record, future tests tell you nothing.
Other components
Backflow preventers get a forward flow test at system demand, pressure-reducing valves are tested under flow, and fire pumps get an NFPA 20 acceptance test. For pump settings see commissioning fire pump pressure settings.
Acceptance documents and handover
- Contractor's material and test certificates: separate for aboveground and underground, signed by the installing contractor and the witnessing parties.
- Hydraulic design information sign and any required general information sign at the riser.
- As-built drawings and an updated hydraulic calculation.
- Equipment list with listing and approval documents.
- Operation and maintenance instructions and an NFPA 25 test programme.
- Spare sprinkler cabinet and wrenches.
Where antifreeze is used, record that new systems use only antifreeze solutions listed for the purpose, and that concentration has been measured.
Acceptance day checklist
- Is the underground flushing record signed and dated before the aboveground connection?
- Is the hydrostatic gauge calibrated and at the lowest point, with start and finish times recorded?
- For dry systems, are 24-hour air test records, trip time and water delivery time captured?
- Has every control valve been closed and its supervisory signal seen at the panel and the monitoring centre?
- Has the waterflow alarm and its retard setting been proven through the inspector's test?
- Were static and residual pressures recorded in the main drain test?
- Has the pump acceptance curve been compared with the design curve?
- Is the hydraulic sign on the riser and the spare sprinkler cabinet in place?
Common mistakes
- Cutting the hydrostatic test short, or reading pressure at the highest point.
- "Sealing" leaks with additives during the test.
- Skipping the dry system air test.
- Not measuring water delivery time.
- Not recording main drain test values.
- Certificates completed without witness signatures.
Acceptance day tip: share a written test plan before the day, with the criterion, measuring point, responsible person and witness for each test. Acceptance is about measurement and records, not a demonstration. For first filling and pressurisation see system filling and pressurisation.
Frequently Asked Questions
What is the hydrostatic test pressure and duration for sprinkler systems?
The general criterion is 13.8 bar (200 psi) for 2 hours. Where maximum working pressure exceeds 10.3 bar (150 psi), the test pressure is 3.4 bar (50 psi) above maximum working pressure.
How is a dry system air test carried out?
In addition to the hydrostatic test, the system is held at 2.8 bar (40 psi) air for 24 hours; pressure loss must not exceed 0.1 bar (1.5 psi).
Why does the acceptance main drain test matter?
The static and residual pressures become the reference for periodic tests over the system's life. Supply deterioration or a partly closed valve can only be spotted against that baseline.
Can leak sealants be used during hydrostatic testing?
No. No leak sealant or corrosive additive goes in the test water; a leaking joint is repaired and the test repeated.
SprinkCalc — Fire Sprinkler Design Across Three Standards
SprinkCalc covers hazard classification, design density and area, K-factor selection, water demand and hydraulic calculations for NFPA 13, FM Global and BS EN 12845 in a single iOS app, and exports a professional PDF report.
Download SprinkCalc on the App StoreNFPA 13 (current edition) – system acceptance; NFPA 24 – flushing and testing of underground mains; NFPA 20 – pump acceptance testing; NFPA 25 – periodic inspection and testing. Numeric values are general criteria; confirm against the edition in force and the authority having jurisdiction for each project. The findings here are typical defect patterns, not an account of events at any particular site.