Fire Department Connection Calculator
FDC requirements from system type and demand.
About this calculator
This calculator determines how many fire department connections (FDCs) a building needs and how they should be sized, based on NFPA 13 Section 6.8 and NFPA 14. The key branch is in how it totals flow demand: for a combined sprinkler-and-standpipe system sharing the same piping, it takes the larger of the two demands rather than adding them, since they draw from the same water supply; but if you specify separate FDCs for sprinkler and standpipe, it sums both demands and requires two FDC assemblies. From the resulting total flow, it sizes inlets at roughly 250 GPM per 2.5-inch connection, and recommends a single 4-inch Storz coupling once demand exceeds 500 GPM (since one 4-inch Storz can generally handle up to about 1,000 GPM), switching to multiple Storz connections above that. Required pressure at the FDC inlet combines a residual pressure floor (100 psi when standpipe-only or combined sprinkler-and-standpipe is selected, 50 psi for sprinkler-only or for separate sprinkler-plus-standpipe FDCs), a static elevation component at 0.433 psi per foot of building height, and a flat 15 psi placeholder for interior friction loss — then flags whether a typical fire department pumper's 150 psi ceiling can meet that demand.
It also checks your entered hydrant distance against NFPA's 100-foot placement limit. The 15 psi friction allowance is a rough stand-in, not a hydraulic calculation of your actual piping, so for a real submittal you'll still need the project's full hydraulic analysis to confirm delivered pressure. FDC style (wall-mounted, freestanding post, or pit/flush type) is collected for the record but doesn't currently affect any of the sizing or pressure results above.
Inputs
Results
Total FDC flow (GPM)
500
FDC connections needed
1
Figures current as of 2026. Source: National Fire Protection Association, NFPA 13, Standard for the Installation of Sprinkler Systems, Section 6.8; NFPA 14, Standard for the Installation of Standpipe and Hose Systems
How to Use This Calculator
- Enter System type served, Sprinkler demand (GPM), and Standpipe demand (GPM).
- Set Building height (ft), Distance to hydrant (ft), and FDC style.
- Review Total FDC flow (GPM) and FDC connections needed.
- Use Inlet connections and Required FD inlet pressure (PSI) to inform your decision.
How the result changes with Standpipe demand (GPM)
| Standpipe demand (GPM) | Total FDC flow (GPM) | FDC connections needed |
|---|---|---|
| 250 | 250 | 1 |
| 375 | 375 | 1 |
| 750 | 750 | 1 |
| 1,250 | 1,250 | 1 |
What each input means
- System type served
- The fire protection system(s) the FDC serves.
- Sprinkler demand (GPM)
- Total sprinkler system flow demand from hydraulic calculations.
- Standpipe demand (GPM)
- Standpipe system flow demand per NFPA 14.
- Building height (ft)
- Height from FDC to highest outlet served.
- Distance to hydrant (ft)
- Distance from FDC to nearest fire hydrant. Must be ≤100 ft per NFPA.
- FDC style
- 1=Wall-mounted, 2=Freestanding post, 3=Pit/flush type.
What each result means
- Total FDC flow (GPM)
- Total flow the FDC must accommodate.
- FDC connections needed
- Number of separate FDC assemblies required.
- Inlet connections
- Number of 2.5" or 4" inlets needed.
- Required FD inlet pressure (PSI)
- Pressure the fire department pumper must deliver at the FDC.
- Elevation pressure (PSI)
- Static head from FDC to highest outlet.
- FD pumper capacity OK
- 1=Typical pumper (150 PSI) can supply, 0=May need relay pumping.
- Hydrant distance OK
- 1=Within 100 ft, 0=Exceeds NFPA requirement.
- Check valve required
- Always 1. Check valve prevents backflow from system into FDC.
- Signage type
- 1=AUTO SPKR, 2=STANDPIPE, 3=AUTO SPKR & STANDPIPE.
- 4" Storz sufficient
- 1=Single 4" Storz coupling is adequate, 0=Need multiple connections.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersSystem type served = 3, Sprinkler demand (GPM) = 250, Standpipe demand (GPM) = 500, Building height (ft) = 50 = 6 input(s) provided
- Calculate Total FDC flowTotal FDC flow500 = 500
- Calculate FDC connections neededFDC connections needed1 = 1
- Calculate Inlet connections2 = 2
- Calculate Required FD inlet pressureRequired FD inlet pressure = residualPSI + elevationPressurePSI + frictionEstimatePSI136.7 = 136.7
Figures and sources
- NFPA 13 Section 6.8 and NFPA 14 fire department connection placement and sizing (100 ft hydrant proximity, 18-48 in AFF, flow thresholds) (2026) — National Fire Protection Association, NFPA 13, Standard for the Installation of Sprinkler Systems, Section 6.8; NFPA 14, Standard for the Installation of Standpipe and Hose Systems
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the combined sprinkler-and-standpipe option take the larger of the two demands instead of adding them together?
When a single FDC feeds a combined system, both the sprinklers and the standpipe draw from the same shared piping and water supply, so they can't both demand their full flow simultaneously the way two independent systems would. The calculator instead uses whichever of Sprinkler Demand or Standpipe Demand is larger as the design flow — switching to the "Separate sprinkler + standpipe" option is what tells it to sum both demands and size two independent FDC assemblies instead.
When does the calculator recommend a single 4-inch Storz coupling instead of dual 2.5-inch Siamese inlets?
Below 500 GPM total flow it recommends either 2 × 2.5" Siamese or 1 × 4" Storz as roughly equivalent options; between 500 and 1,000 GPM it prefers the 4" Storz since a single large coupling can handle that flow more efficiently than stacking more 2.5" inlets; above 1,000 GPM it switches to multiple 4" Storz connections, sized at one per 750 GPM of demand.
Why does required residual pressure differ between 100 psi and 50 psi depending on system type?
The calculator uses 100 psi whenever the system serves a standpipe (Standpipe Only or Combined), matching NFPA 14's higher pressure requirement for fire department hose operations at the top floor, and drops to 50 psi for Sprinkler Only or the Separate sprinkler + standpipe option, reflecting a sprinkler system's lower typical residual demand. That residual figure is then added to elevation pressure and a flat 15 psi friction allowance to get the total pressure the fire department pumper must supply.
What does it mean if Hydrant Distance OK comes back as No?
It means your entered Distance to Hydrant exceeds the 100-foot placement limit NFPA 13 Section 6.8 and NFPA 14 require between the FDC and the nearest usable fire hydrant, which exists so firefighters can quickly connect a supply line without running excessive hose. If that flag is No, the practical fix is usually relocating the FDC closer to an existing hydrant or working with the water utility to add one nearby, not changing anything in this calculator.
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