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How to Use the Boiler Feed Pump Calculation Calculator
1. Enter your boiler steam generation rate
Type in your boiler's rated output in kg/hr or lb/hr. This is the core figure everything else builds on — it sets the minimum continuous feedwater flow the pump must deliver. If your boiler nameplate shows evaporation rate rather than steam output, those two figures are equivalent for sizing purposes.
2. Enter feedwater temperature and boiler steam pressure
Feedwater temperature affects liquid density, which converts your mass flow into volumetric flow — the unit pumps actually work with. Steam pressure drives the minimum head the pump must develop just to push water through the feed check valve into the drum. Higher pressure boilers need pumps with more stages and higher speed to reach the required head.
3. Enter expected pump efficiency
Pump efficiency directly controls how much shaft power your motor needs to supply. A realistic efficiency figure comes from the pump manufacturer's curve at your expected operating point. If you are still in early-stage sizing and do not have a curve yet, 70% is a reasonable starting estimate for a standard multistage centrifugal boiler feed pump.
4. Review your results — flow, head, power, and motor size
The calculator converts mass flow to volumetric flow using feedwater density, builds up total dynamic head from boiler pressure and system losses, applies the hydraulic power formula, and then rounds up to the next practical motor rating with an operating margin. Use these results to shortlist pumps and start discussions with suppliers.
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Boiler Feed Pump Calculation Calculator Formulas
Feedwater flow rate
Volumetric Flow (m³/hr) = Mass Flow (kg/hr) ÷ Density (kg/m³)
Pumps are sized on volumetric flow, not mass flow. Feedwater density changes with temperature — water at 80°C is less dense than water at 20°C — so using the correct density at your actual feedwater temperature is important for an accurate result. At 80°C, water density is approximately 972 kg/m³ compared with 998 kg/m³ at 20°C.
Total dynamic head
TDH (m) = Boiler Pressure Head + Static Head + Friction Losses + Control Valve ΔP + Safety Margin
Total head is the sum of every resistance between the pump discharge and the boiler drum. Boiler pressure head dominates in most systems and is calculated by converting bar or psi into equivalent metres of water head. The safety margin — typically 10–15% of the subtotal — protects against unforeseen pressure drops and control instability.
Hydraulic shaft power
Power (kW) = (Q × H × ρ × 9.81) ÷ (η × 1,000)
Q is volumetric flow in m³/s, H is total head in metres, ρ is fluid density in kg/m³, and η is pump efficiency expressed as a decimal (for example, 0.70 for 70%). The result is the shaft power the motor must supply. Always select a motor rated above this figure — a 10–15% service factor is standard practice in industrial steam plant design.
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Key Factors
Required flow rate
Steam generation rate is the starting point, but the final pump design flow is always higher. Continuous blowdown (to control dissolved solids), recirculation flow through the minimum flow bypass, and a standby capacity margin all add to the flow the pump must be capable of delivering. Omitting these additions leads to undersized pumps that run at their limits and fail prematurely.
Total head requirement
Head is the most technically demanding part of boiler feed pump sizing. Apart from boiler operating pressure — which sets the floor — you need to account for the pressure drop through the feed regulating valve (often 30–50% of boiler pressure in modulating systems), economiser pressure drop, piping and fitting losses, and static lift if the pump sits below the boiler feed nozzle elevation.
Pump efficiency and motor selection
A pump running away from its best efficiency point (BEP) consumes more power, generates more heat, and wears faster. Selecting a pump whose BEP aligns closely with your design operating point reduces energy costs over the life of the plant and lowers maintenance frequency. Motor selection should match shaft power requirements with a sensible service factor — neither oversized to the point of poor power factor, nor so tight that transient loads risk overload trips.
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Sizing Guide
Small boilers
Up to 5,000 kg/hr steam output
Package boilers in this range typically work with single or two-stage centrifugal pumps. Even at smaller scale, always include a recirculation bypass and protect the pump against dead-head operation. Simple ON/OFF pump control with level-based start/stop is common, but a properly set minimum flow orifice is still essential.
Medium boilers
5,000 to 25,000 kg/hr steam output
This is the range where pump selection decisions have the most impact on operating cost. Two or three alternative pump duty points are worth comparing. Suction conditions, available NPSH, and the shape of the pump curve across the operating load range all deserve careful attention. Variable speed drives (VSDs) become cost-effective in this band and can significantly reduce energy consumption at part load.
Large boilers
Above 25,000 kg/hr steam output
High-capacity systems almost always justify multistage pump selection, standby pump philosophy (100% installed spare as a minimum), detailed NPSH analysis, and hydraulic modelling of the complete feedwater system. Motor starting method, shaft seal type, and bearing selection all warrant specialist review. These projects benefit from full collaboration between the pump vendor, boiler manufacturer, and instrumentation engineer from the earliest design stage.
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Frequently Asked Questions
Disclaimer
This calculator is designed for preliminary engineering guidance and educational purposes. The results give a useful starting point for pump selection discussions but should not be used as the sole basis for final equipment specification. Accurate boiler feed pump sizing always requires detailed system modelling, verified pipe loss calculations, full NPSH analysis, steam table data at actual operating conditions, and review of manufacturer pump curves against your specific duty point.