In sizing NFPA 20 fire pumps, what does the term system demand describe?

• A. The hydraulic load the system requires at worst-case conditions, determining the needed pump capacity.
• B. The maximum flow the pump can deliver at any time.
• C. The minimum head required to start the pump.
• D. The energy consumption at design conditions.

Answer: (A)

System demand is the hydraulic load the fire protection system requires from the pump under worst‑case conditions, and that load determines the pump capacity needed. When sizing NFPA 20 pumps, you look at the most demanding scenario the system could present—the combination of the greatest required flow and the corresponding head (pressure) due to friction, elevation, and any station pressures. The pump must be able to deliver at least that amount of flow at that head across its operating range, which sets the appropriate pump size and rating. This concept is about what the system requires, not what the pump can always deliver or the energy used. For example, if the worst case calls for 1,000 gpm at 150 ft of head, the pump must be sized to meet or exceed that demand at that head.