Fire Pump Sizing Calculator: engineer's guide
A fire pump must deliver 100% flow at 100% head, 150% flow at 65% head, and churn pressure ≤ 140% of rated head per NFPA 20.
Open the Fire Pump Sizing calculator →
What this calculator does
The calculator returns the rated pump duty from the sprinkler and hose demand and confirms the three-point performance envelope requirements.
Formulas used
- Rated flow:
Qrated = Qsprinkler + Qhose + Qhydrant - NFPA 20 3-point rule:
H(1.5 Q) ≥ 0.65 Hrated; H(0) ≤ 1.40 Hrated
Variables
- Qrated = flow at 100% duty, GPM or L/s
- Hrated = head at rated flow
Worked example
Scenario: Sprinkler demand 500 GPM, hose 250 GPM, one hydrant 250 GPM. Target 150 ft rated head.
- Qrated = 500 + 250 + 250 = 1000 GPM
- At 150% flow (1500 GPM) the pump must still deliver ≥ 97.5 ft
- At churn the pump must not exceed 210 ft
- Select a listed 1000 GPM at 150 ft fire pump; verify curve against NFPA 20 envelope
Common mistakes to avoid
- Sizing on sprinkler demand only
- Missing NFPA 20 3-point envelope check
- Skipping the automatic weekly test provision
- Undersizing the driver (electric or diesel) for churn power
Frequently asked questions
Electric or diesel driver?
Electric with emergency generator backup, or diesel where generator not available. NFPA 20 requires two independent sources.
Jockey pump?
Yes — maintains system pressure to prevent nuisance fire pump starts.
Standards and references
NFPA 20, UAE Fire Code, BS EN 12845
Related tools on this site
Open the calculator that pairs with this guide: Fire Pump Sizing Calculator.
Verification note
This guide is planning support only. Final design must be verified against the applicable project specification, authority requirements, manufacturer data, and the standards cited above. Consult a licensed engineer for construction-issue calculations.