Built around boiler duty
Calculate from maximum steam generation or begin with a known feedwater flow when the plant duty is already established.
Free online engineering calculator
Boiler Feed Pump Calculation Without the Guesswork
Estimate the feedwater flow, total dynamic head, pressure rise, NPSH available, pump power and practical motor size for a steam boiler system. Start with a quick duty-point check, or open Advanced mode when you have site losses, elevations and suction data.
- Metric and US units
- Quick and advanced sizing
- No signup required
Feedwater duty overview
Browser based
CalculateDesign Flow
EstimateTotal Head
CheckNPSH Margin
SelectMotor Size
Boiler Feed Pump Calculation
Calculate design feedwater flow, total dynamic head, differential pressure, NPSHa, hydraulic and shaft power, motor size, pipe velocity, and annual energy cost.
1. Feedwater demand
Flow basis and marginsUse only when bypass flow can occur at the same time as boiler feed flow.
2. Boiler and feedwater conditions
Pressure and fluid propertiesUse deaerator or feed-tank gas-space gauge pressure.
3. System head
Static, friction and equipment lossesPositive when the liquid level is above the pump centreline.
Use estimated total pipe, fitting, valve and economizer losses.
4. Pump, motor and NPSH
Efficiency and operating cost
Preliminary engineering estimate only. Verify applicable boiler code, site conditions, control-valve requirements, minimum-flow arrangement, pump curve, materials, NPSH margin, and motor/service factor with qualified engineers and the equipment manufacturer.
A practical first pass at the real pump duty
A boiler feed pump is not selected from boiler pressure alone. It has to move enough hot feedwater at the required pressure while overcoming elevation, pipe resistance, control-valve drop and other system losses. This free online boiler feed pump calculation tool brings those pieces together so you can build a clear preliminary duty point before opening a manufacturer’s pump curve.
Use the quick calculator when you only know the boiler output, feedwater temperature, pressure and an estimated system loss. It is useful for early estimates, replacing an existing unit, checking a supplier quotation, or comparing possible pump and motor sizes.
Switch to Advanced mode when better plant information is available. You can enter suction-vessel pressure, tank and discharge elevations, separate suction and discharge losses, economizer pressure drop, control-valve allowance, NPSHr, pipe diameters and annual operating hours. The result is still an estimate, but it is a much more useful one.
The final equipment choice should always be checked at the actual operating point. Pump efficiency, NPSHr and allowable operating range come from the manufacturer’s tested curve—not from a general calculator.
Hot-water properties
The estimate adjusts water density and vapour pressure with temperature instead of treating every system as cold water.
Transparent results
Open the calculation breakdown to see where flow, head, power and NPSH values come from before using them for pump selection.
How to Use the Boiler Feed Pump Calculation & Sizing Calculator
You do not need every detail to get started. Enter the data you trust, use reasonable allowances for what is still unknown, and refine the estimate as drawings, vendor data or plant measurements become available.
Choose the flow basis
Select steam generation when you want the tool to estimate feedwater demand. Choose known feedwater flow when a design flow or measured duty is already available.
Enter feedwater conditions
Add maximum boiler output, continuous blowdown and feedwater temperature. Temperature matters because it changes water density and suction vapour pressure.
Set the pressure duty
Enter boiler operating pressure. In Advanced mode, choose whether the calculation should use operating pressure, safety-valve pressure or the higher of the two.
Add head losses
Include elevation difference, pipe friction, economizer resistance, control-valve pressure drop and other known losses. Avoid hiding every loss inside one large margin.
Use realistic efficiencies
Enter expected pump and motor efficiencies. When certified data is unavailable, use a conservative preliminary estimate and revisit it once a pump curve is selected.
Review the warnings
Check NPSH margin, pipe velocity, required motor output and the full breakdown. Then compare the duty point with the supplier’s performance curve.
Key Formulas Used in Boiler Feed Pump Sizing
The calculator handles the unit conversions automatically, but the sizing logic should never be a black box. These are the core relationships behind the displayed estimates.
Feedwater mass flow
ṁfw = ṁsteam × (1 + blowdown)Maximum steam demand is increased for continuous blowdown. Recirculation and design margin can then be added separately.
Volumetric flow
Q = ṁ / ρPump curves use volumetric flow, so mass flow is divided by the feedwater density at the selected temperature.
Pressure head
Hpressure = ΔP / (ρ × g)The difference between discharge and suction pressure is converted into metres or feet of liquid head.
Total dynamic head
TDH = Hpressure + Hstatic + HlossesSystem losses can include suction and discharge friction, fittings, the feed valve, economizer and other equipment.
Hydraulic and shaft power
Ph = ρ × g × Q × H | Pshaft = Ph / ηpHydraulic power is the useful energy delivered to the water. Shaft power is higher because the pump is not perfectly efficient.
NPSH available
NPSHa = Hsurface + Hstatic,s − Hvapour − Hfriction,sNPSHa describes the suction energy supplied by the system. It must be compared with the pump’s NPSHr at the actual flow.
Do not add pressure and head without converting units. Boiler pressure, valve loss in bar or psi, elevation and pipe friction all need to be expressed on the same head basis before they are combined.
Keep design allowances visible. A flow margin is not the same thing as blowdown, minimum-flow recirculation or head margin. Showing each allowance separately makes the estimate easier to review.
What the Calculator Results Actually Mean
A good calculation does more than produce one motor size. The flow, head, NPSH and power values need to make sense together at the intended operating point.
Design flow
The volumetric rate the pump should deliver after blowdown, recirculation and selected flow margin are considered.
Total dynamic head
The total energy per unit weight needed to overcome boiler pressure, elevation and every included system resistance.
Differential pressure
The TDH expressed as pressure rise at the calculated water density. It is useful when comparing duty with pressure-based specifications.
Shaft power
The mechanical power required at the pump coupling after pump efficiency is applied to the hydraulic requirement.
Motor recommendation
A rounded standard rating above the estimated shaft requirement and selected motor allowance. Confirm service factor and starting method.
NPSH margin
The difference between system NPSHa and manufacturer NPSHr. A positive number alone is not automatically an adequate design margin.
Quick Estimate or Advanced Pump Calculation?
Both modes use the same core sizing logic. The difference is how much of the real feedwater system you describe.
| Calculation area | Quick Sizing | Advanced Mode |
|---|---|---|
| Best used for | Early estimates, concept checks and fast supplier discussions | Detailed preliminary design and review of known plant conditions |
| Flow inputs | Steam duty, blowdown and flow margin | Adds recirculation/minimum-flow allowance and direct-flow options |
| Pressure and head | Operating pressure, elevations and combined losses | Adds safety pressure, suction pressure and separate loss components |
| NPSH | Shows an indicative NPSHa result from simplified suction conditions | Compares NPSHa with entered NPSHr and reports the margin |
| Additional checks | Flow, TDH, power and motor estimate | Pipe velocity, annual energy, cost and detailed engineering breakdown |
A Simple Boiler Feed Pump Calculation Example
Suppose a boiler produces 10,000 kg/h of steam at 10 bar gauge. Feedwater is available at 90°C, continuous blowdown is 3%, and a 15% flow margin is applied. With 7 m of estimated system loss, 1 m net static head, 10% head margin and 70% pump efficiency, the preliminary duty is approximately:
Example inputs
- Maximum steam generation
- 10,000 kg/h
- Continuous blowdown
- 3%
- Feedwater temperature
- 90°C
- Boiler operating pressure
- 10 bar(g)
- Combined losses
- 7 m
- Pump efficiency
- 70%
Approximate outputs
- Base feedwater flow
- 10.67 m³/h
- Design flow after margin
- 12.27 m³/h
- Design TDH
- 125.0 m
- Hydraulic power
- 4.03 kW
- Estimated shaft power
- 5.76 kW
- Preliminary standard motor
- 7.5 kW
This example is intentionally simple. A real project may also need a feed-control-valve allowance, economizer pressure drop, suction-vessel pressure, minimum-flow bypass, standby philosophy and a verified NPSH margin.
From Online Estimate to a Real Pump Selection
Once the free calculation gives you a design flow and TDH, the next step is to place that duty point on a manufacturer’s curve. The selected pump should operate in a stable, efficient region rather than at the far edge of its published range.
Check the pump curve at the calculated flow and head, then review efficiency, absorbed power and NPSHr at that exact point. If the system operates across a wide demand range, look beyond the single design point and consider how the control valve, variable-speed drive or recirculation arrangement changes the operating condition.
For hot feedwater, suction design deserves special attention. A high tank temperature raises vapour pressure and reduces the available NPSH. Tank elevation, suction-pipe diameter, fittings, strainers and deaerator pressure can all influence cavitation risk.
Finally, confirm materials, mechanical seal arrangement, bearing design, allowable temperature, duty/standby philosophy and motor electrical details with the manufacturer or responsible engineer.
Common Boiler Feed Pump Sizing Mistakes
Most poor estimates are not caused by difficult mathematics. They come from missing an operating condition, using the wrong pressure basis, or applying margins without understanding what they cover.
Using steam flow with no allowance
Blowdown and minimum-flow recirculation can increase the actual pump flow above the net steam-production rate.
Ignoring the feed valve
A modulating control valve needs pressure drop to regulate flow. Leaving it out may produce an unrealistically low head estimate.
Treating hot water as cold
Density changes the flow and head conversion, while vapour pressure has a direct effect on NPSHa.
Mixing gauge and absolute pressure
Gauge values may be suitable for differential pressure, but NPSH calculations require absolute pressure.
Choosing a motor too tightly
The motor needs to cover absorbed power at the real duty and expected operating range—not only one rounded calculation point.
Skipping the pump curve
A calculator estimates system duty. It cannot confirm efficiency, NPSHr or operating stability for a specific pump model.
Boiler Feed Pump Calculation FAQs
These answers cover the questions that usually come up when someone is estimating feedwater flow, head, NPSH and motor size for the first time.
What does a boiler feed pump calculation determine?
It estimates the pump duty needed to move feedwater into a boiler. A useful calculation includes design flow, total dynamic head, pressure rise, hydraulic and shaft power, motor allowance and a suction-side NPSH check.
Can I calculate pump size from boiler capacity?
Yes, boiler steam output can be used as the starting mass flow. Add continuous blowdown and any legitimate recirculation or design allowance, then convert the result to volumetric flow using feedwater density.
How much flow margin should I use?
There is no universal percentage for every boiler plant. The correct allowance depends on control method, blowdown, minimum-flow bypass, operating variation and applicable design practice. Keep each allowance visible instead of using one unexplained multiplier.
Why is total dynamic head higher than boiler pressure head?
The pump must overcome more than the pressure inside the boiler. Static elevation, pipe and fitting losses, economizer resistance, control-valve pressure drop and an appropriate head allowance can all add to TDH.
What efficiency should I enter?
Use the expected efficiency at the actual duty point whenever a manufacturer curve is available. For an early estimate, enter a conservative value that reflects the likely pump type and size, then update it during equipment selection.
What is the difference between NPSHa and NPSHr?
NPSHa is supplied by the system and is calculated from suction pressure, elevation, vapour pressure and suction losses. NPSHr is a characteristic of the selected pump and comes from its tested curve. The available value must exceed the required value by an acceptable margin.
Does this tool replace pump-vendor software?
No. It is designed to calculate and communicate a preliminary duty point. Final selection needs a certified curve, detailed plant data, equipment limits and review by the responsible engineer or pump manufacturer.
Can I use the calculator in US units?
Yes. Switch the unit control to US Units to work with psi, feet, Fahrenheit, inches, GPM and horsepower while the calculation engine keeps the conversions consistent.
Ready to estimate your boiler feed pump duty?
Run the free online calculation, review the full breakdown, and save or print the results for your next design check or supplier discussion.
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