In the design and operation of fire pump systems, two critical parameters often come up — shutoff head and rated head. Both are essential for understanding the performance of a fire pump, yet they serve very different purposes. Confusing one for the other can lead to improper pump selection, inefficient performance, or even failure to meet NFPA 20 and UL standards.
This article explains in detail what shutoff head and rated head mean, how they are determined, and why understanding their difference is vital for every fire protection professional.
Before diving into shutoff and rated head, it’s important to first understand what “head” means in pump terminology.
In simple terms, head represents the energy that a pump imparts to the water, typically measured in meters (m) or feet (ft). It’s the vertical height the pump can raise water, and it directly correlates to pressure (1 meter of head ≈ 0.098 bar, or 1 foot ≈ 0.433 psi).
In fire protection systems, head determines how much pressure the pump can generate to deliver the required water flow throughout the system — from the suction side to the farthest sprinkler or hydrant outlet.
Rated head (sometimes called “duty head”) is the pressure that the pump delivers at its rated flow. It is the performance point at which the pump is officially designed and certified to operate.
For a UL Listed or NFPA 20 compliant fire pump, this is the point used to define its model, nameplate, and performance curve. For example, a pump rated at 1000 GPM @ 100 PSI means that at a flow of 1000 gallons per minute, the pump will produce 100 psi of discharge pressure at the rated speed.
It is the primary design point for the pump.
Determines the pump’s nameplate performance (e.g., 750 GPM @ 120 PSI).
Used for certification and acceptance testing according to NFPA 20 and UL/FM standards.
The rated head represents the efficient working zone of the pump.
In operation, this is the pressure the fire pump should provide during an actual fire event when the system demands its full flow capacity.
Shutoff head is the maximum head (pressure) the pump can generate when there is zero flow — meaning the discharge valve is closed.
At this condition, the impeller is still rotating, creating pressure, but no water is being discharged. This represents the upper limit of the pump’s pressure capability.
Occurs at zero flow (no discharge).
Represents the maximum pressure a pump can develop.
Used to define the safe operating range and to prevent overpressure damage.
Typically 120% to 140% of the rated head, depending on pump design.
For example, a pump rated at 100 PSI may have a shutoff head between 120 PSI and 140 PSI.
Both shutoff head and rated head are points on a fire pump performance curve, which plots head (pressure) versus flow.
Here’s how they relate:
Shutoff head is at the far left of the curve (zero flow).
Rated head is at the nominal flow point (e.g., 100% of rated capacity).
Between these points lies the operating range — typically from 0% to 150% of the rated flow.
The curve shows how pressure decreases as flow increases. When the pump operates at rated flow, it provides the designed head. When the flow stops, the pressure rises to the shutoff head.
This relationship helps engineers ensure that the pump will perform reliably under all fire conditions, from idle standby to full discharge.
NFPA 20 — Standard for the Installation of Stationary Pumps for Fire Protection — and UL/FM certification standards define strict performance criteria for both rated and shutoff head.
According to NFPA 20, the fire pump must:
Deliver 100% of rated flow at rated head.
Deliver 150% of rated flow at not less than 65% of rated head.
Not develop more than 140% of rated head at shutoff.
During acceptance testing, these three points (0%, 100%, and 150% flow) are tested and plotted to verify that the fire pump meets its certified curve.
This ensures that the pump can operate safely, efficiently, and within limits under all possible system demands.
Understanding the difference between shutoff and rated head is not just academic — it has practical implications for fire system design, performance, and safety.
If a fire pump consistently operates near its shutoff head (for example, due to closed valves or low system demand), excessive pressure can stress pipes, valves, and fittings. Knowing the shutoff head helps engineers install pressure relief valves and set safe limits.
Designers must select pumps with a rated head that matches system requirements. If the rated head is too low, the system may fail to deliver water to the most remote outlet. If too high, it may cause overpressurization.
NFPA 20 and UL standards use both rated and shutoff head to confirm that the pump performs within acceptable ranges. Understanding these terms ensures compliance during inspection and certification.
Operating the pump near its rated point ensures maximum efficiency and reduces wear. Running too close to shutoff can cause overheating and internal recirculation, damaging the impeller and seals.
When a fire pump doesn’t deliver expected pressure, knowing both rated and shutoff head helps maintenance teams diagnose whether the issue is due to system restriction, impeller wear, or motor speed problems.
Consider a fire pump rated at 750 GPM @ 120 PSI.
Rated Head: 120 PSI at 750 GPM
Shutoff Head: 150 PSI (125% of rated head)
150% Flow Point: 1125 GPM at 78 PSI
This means:
When the system demands 750 GPM, the pump delivers 120 PSI — its optimal performance point.
If all discharge outlets are closed, the pump pressure will rise to 150 PSI — the shutoff head.
If demand increases to 1125 GPM, pressure will drop to 78 PSI, still within NFPA 20 limits.
By understanding these points, engineers and operators can evaluate pump performance and ensure system reliability during both testing and emergency operation.
Some assume the highest pressure reading on a gauge reflects normal operation. In reality, that’s the shutoff head, not the working pressure. Continuous operation at this pressure is unsafe and can damage the system.
A higher shutoff head doesn’t necessarily indicate better quality. It only shows the pump’s ability to generate pressure at zero flow. A well-designed pump balances efficiency, stability, and compliance with NFPA limits.
Rated head is achieved under specific test conditions — including speed, suction pressure, and water temperature. Deviations from these factors in the field can slightly alter actual performance.
Check the system demand curve — ensure rated head matches building height and sprinkler pressure requirements.
Confirm shutoff head compliance — it must not exceed 140% of rated head.
Verify NPSH (Net Positive Suction Head) — to avoid cavitation at all flow conditions.
Use relief valves if shutoff head exceeds system design pressure.
Consult certified pump curves from UL or FM approved manufacturers to confirm performance.
By considering both rated and shutoff head, designers ensure safe and efficient pump operation throughout the fire system’s lifecycle.
The difference between shutoff head and rated head defines how a fire pump performs under various conditions — from idle to full discharge.
Rated head is the designed working pressure at rated flow.
Shutoff head is the maximum pressure at zero flow.
Understanding both ensures safe operation, system integrity, and compliance with NFPA 20 standards.
For fire protection engineers, installers, and system owners, recognizing how these parameters influence performance is key to reliable firefighting readiness. When selecting or testing a fire pump, always refer to certified curves and ensure the pump operates within its designed range.
A properly selected and tested fire pump not only meets regulatory requirements but also ensures that, when the time comes, it performs its life-saving role flawlessly.
