What Does This Boiler Feed Pump Head Calculator Do?
This calculator estimates the total dynamic head required from a boiler feed pump. It begins with the pressure difference between the boiler and the feedwater source, converts that pressure difference into metres or feet of hot-water head, and then adds the net elevation rise, pipe and fitting friction, economizer or equipment losses, and the required pressure drop across the feedwater control valve.
A separate design margin is applied only after the base system head has been calculated. The result can support concept design, pump-enquiry preparation, quotation checks, replacement studies and preliminary comparison of pump curves.
The tool calculates head, not flow. Establish the design feedwater flow first because pipe friction, equipment pressure drop and control-valve pressure drop all depend on the operating flow. It assumes the velocity-head difference between the selected source and destination datums is negligible; include any material velocity effect in the stated system-loss allowance.
Boiler Feed Pump Head Formula
The calculator uses the steady-flow energy equation in a practical form. Pump head must overcome the pressure difference between the source and destination, the change in elevation and the hydraulic losses through the feedwater system.
Pressure head = (Boiler pressure − Source pressure) ÷ (Water density × g)Base pump head = Pressure head + Elevation rise + Pipe friction head + Equipment head + Control-valve headDesign pump head = Base pump head × (1 + Head margin % ÷ 100)
Loss head = Pressure drop ÷ (Water density × g)
ΔP = Water density × g × Design pump head
In SI calculations, pressure is converted to pascals, density is entered in kg/m³ and gravitational acceleration is taken as 9.80665 m/s². The result is metres of the pumped liquid. US-unit entries are internally converted to the same engineering basis and displayed in feet and psi.
How to Use the Calculator
- Select Metric or US Units. Metric mode uses bar, metres and °C. US mode uses psi, feet and °F.
- Enter boiler operating pressure. Use the pressure corresponding to the maximum design feedwater duty.
- Enter feedwater-source pressure. Use the pressure at the deaerator or feed-tank liquid surface. Enter zero gauge pressure for a vented atmospheric tank.
- Enter the net elevation rise. Measure vertically from the source liquid level to the boiler feedwater inlet or other selected destination datum.
- Add pipe and fitting friction. Use the loss calculated at the same design flow used for pump selection.
- Add equipment pressure losses. Include the economizer, check valve, flowmeter, strainer and other losses not already included in the friction value.
- Enter the control-valve pressure drop. Use the differential pressure required across the feedwater valve at maximum flow.
- Enter feedwater temperature and margin. Temperature adjusts density; the margin is applied once to the completed base head.
Understanding the Results
Pressure-difference head
This is the liquid head needed to overcome the difference between boiler pressure and feedwater-source pressure. A pressurised deaerator reduces the required pressure difference compared with an atmospheric feed tank, although its effect must be calculated together with elevation and system losses.
Base system head
The base head is the sum of pressure head, elevation rise, pipe friction, equipment loss and control-valve head before the design margin. This is the hydraulic duty established from known system conditions.
Design pump head
The design head is the base system head after the entered margin. It is the main value to use when preparing a preliminary pump duty point together with the required feedwater flow.
Equivalent differential pressure
This is the pressure rise corresponding to the calculated design head at the estimated feedwater density. It is useful when comparing the result with pressure-based equipment data, but centrifugal-pump curves are normally presented as head versus flow.
Estimated water density
The calculator interpolates liquid-water density over its temperature range. Density affects the conversion between pressure and head: the same pressure difference corresponds to more metres of head when the liquid density is lower.
Worked Example
Consider a boiler operating at 10 bar(g), supplied from a pressurised deaerator at 0.2 bar(g). The boiler inlet is 8 m above the deaerator liquid level. Pipe and fitting loss is 12 m, the economizer and other equipment account for 0.8 bar, and the feedwater control valve requires 1.5 bar. Feedwater temperature is 105°C and the selected head margin is 10%.
| Component | Calculation basis | Approximate head |
|---|---|---|
| Boiler minus source pressure | 10.0 − 0.2 = 9.8 bar | 104.67 m |
| Net elevation rise | Entered directly | 8.00 m |
| Pipe and fitting friction | Entered at design flow | 12.00 m |
| Economizer and equipment loss | 0.8 bar converted at 105°C | 8.55 m |
| Control-valve drop | 1.5 bar converted at 105°C | 16.02 m |
| Base system head | Sum of all components | 149.24 m |
| Design pump head | 149.24 × 1.10 | 164.16 m |
The preliminary duty is therefore approximately 164 m of head, equivalent to about 539 ft or 15.37 bar differential pressure at the estimated feedwater density. This head must be paired with the design flow before a pump curve can be reviewed.
What Values Should You Enter?
Use one internally consistent operating case. Combining the maximum boiler pressure from one case with friction losses from a lower-flow case can produce an unrealistic result.
Boiler pressure
Use the boiler or economizer outlet pressure that the feedwater pump must overcome at the selected duty. Clearly distinguish normal operating pressure, maximum operating pressure and safety-valve set pressure.
Source pressure
Enter the pressure at the feed-tank or deaerator liquid surface. A pressurised deaerator provides positive source pressure; an open tank is approximately 0 bar(g).
Elevation rise
Use the vertical difference between the selected source and destination liquid or connection datums. Do not substitute total pipe length for vertical elevation.
Friction and minor losses
Calculate pipe, bend, tee, isolation-valve and fitting losses at the design flow. Friction normally changes significantly when flow changes.
Equipment pressure drop
Use vendor or project data for the economizer, check valve, strainer, flow element and other inline components at the applicable flow.
Control-valve drop
Provide enough differential pressure for stable control at maximum feedwater flow. Confirm the selected value during control-valve sizing.
Components of Boiler Feed Pump Total Dynamic Head
Pressure head
The pump must raise feedwater from source pressure to boiler-side pressure. This is often the largest component in a high-pressure feedwater system.
Static elevation
A higher boiler inlet adds positive head. A destination below the source liquid level can reduce the static component, although pressure and losses may still dominate.
Pipe friction
Friction occurs in straight pipe and rises with flow. It must be evaluated using the selected pipe size, roughness, length, temperature and flow.
Minor losses
Bends, tees, reducers, isolation valves and check valves create additional resistance. Include them either in the friction calculation or as separate losses, but not both.
Economizer loss
Economizers and other heat-transfer equipment can impose a material pressure drop. Use supplier data at the design feedwater flow where available.
Control-valve authority
A modulating feedwater valve requires differential pressure to regulate flow. The available valve drop changes with pump head, boiler pressure and system friction.
Gauge Pressure Versus Absolute Pressure
Do not mix gauge and absolute values. Boiler data are commonly stated in bar(g) or psig, while thermodynamic calculations may use absolute pressure. This calculator uses only the pressure difference for head, so either basis works when both source and boiler pressures use the same reference.
For example, 10 bar(g) at the boiler and 0.2 bar(g) at the deaerator produce a 9.8 bar difference. Adding atmospheric pressure to both values changes the absolute numbers but not the difference.
Why Feedwater Temperature Matters
Pump head is energy per unit weight, while pressure is force per unit area. The relationship between the two depends on liquid density. Hot feedwater is less dense than cold water, so a fixed pressure difference converts to a larger head in metres or feet at higher temperature.
Temperature also matters for suction performance and NPSH, but this calculator does not perform a vapour-pressure or NPSH calculation. Treat the density estimate as a preliminary conversion for liquid water and confirm properties with project-approved steam tables or fluid-property software.
Head, Boiler Pressure and Pump Discharge Pressure Are Not the Same
Boiler pressure is only one part of the system duty. Pump head must also cover the source pressure relationship, elevation, pipe friction, control-valve differential and equipment losses. Selecting a pump solely by adding an arbitrary pressure allowance above boiler pressure can overlook important system components.
Likewise, the calculated differential pressure is not automatically the pressure that a discharge gauge will read. Gauge location, suction pressure, local elevation, velocity and losses between the pump and gauge affect the measured value.
Common Boiler Feed Pump Head Calculation Mistakes
- Using boiler pressure alone: this ignores the feedwater-source pressure, elevation and hydraulic losses.
- Mixing gauge and absolute pressures: the source and destination pressures must use the same reference.
- Using friction from the wrong flow: head loss changes with flow and should be calculated at the design feedwater rate.
- Counting the same loss twice: do not include a valve or fitting in both the pipe-friction result and a separate equipment allowance.
- Ignoring control-valve drop: a modulating valve needs adequate differential pressure to pass and control the required flow.
- Applying several hidden margins: establish the base head first, then apply one clearly documented project margin.
- Using cold-water pressure conversions: hot-water density changes the relationship between bar or psi and metres or feet of head.
- Treating head as complete pump selection: flow, NPSH, efficiency, power, minimum-flow protection, materials and pump curves still require review.
How to Use the Result for Pump Selection
Pair the calculated design head with the design feedwater flow to define the preliminary duty point. Compare this point with a manufacturer’s certified pump curve, including the expected minimum and maximum operating cases rather than checking only one point.
Next, calculate NPSH available from the feed tank or deaerator to the pump suction and compare it with the manufacturer’s NPSH required, including the project’s specified margin. Review minimum continuous stable flow, recirculation arrangements, absorbed power, motor rating, speed, materials, seal system and allowable operating region.
For variable-speed or control-valve systems, develop a system curve and review the duty over the anticipated load range. Boiler pressure, friction loss and valve differential may all vary as steam and feedwater flow change.
Frequently Asked Questions
What is total dynamic head for a boiler feed pump?
It is the total energy per unit weight the pump must add to overcome the pressure difference, elevation change and all hydraulic losses between the feedwater source and the boiler-side destination at the selected flow.
Should boiler feed pump head be higher than boiler pressure?
The pump must provide enough differential head to overcome boiler-side pressure plus elevation and losses, after accounting for the pressure available at the feedwater source. The required differential is therefore not determined by boiler pressure alone.
Can I enter an atmospheric feed tank?
Yes. Enter 0 bar(g) or 0 psig as the source pressure. Also enter the correct source liquid-level elevation and calculate the suction-side NPSH separately.
Why is control-valve pressure drop included?
A feedwater control valve needs a pressure differential to pass and regulate the required flow. If this loss is omitted, the pump may not provide adequate valve authority at maximum duty.
Does this calculator include suction-pipe losses?
The head calculation is framed from the source liquid surface to the boiler-side destination. Losses that belong to that defined system path should be included consistently. Suction losses are also essential in the separate NPSH-available calculation.
What head margin should I use?
Use the allowance defined by the project design basis, client specification or engineering standard. Avoid applying a universal margin without checking whether individual inputs already contain allowances.
Can this calculator select the final pump?
No. It establishes a preliminary head requirement. Final selection also needs flow, NPSH, pump and system curves, efficiency, power, minimum-flow protection, materials and manufacturer review.
Engineering basis: total pump head is treated as the combination of pressure, elevation and friction or resistance losses. Control-valve and inline-equipment pressure drops are entered separately so the calculation remains transparent and auditable.