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Enter operating values below and get instant boiler feed pump sizing results for flow rate, total head, power, and motor recommendation.
Final values shown in metric units for engineering consistency.
| Box 1 | Box 2 | Box 3 |
|---|---|---|
| 📐 Formula Source | ⚙️ Typical Efficiency | 🌡️ Temp Range Supported |
| IAPWS-IF97 Steam Tables | 65% – 85% | 0°C to 200°C |
A boiler feed pump calculation determines the flow rate, total head, shaft power, and motor size needed to supply feedwater to a boiler drum at the correct pressure and volume. The calculation takes four inputs — boiler evaporation capacity, feed water temperature, steam drum pressure, and pump efficiency — and applies standard thermodynamic formulas derived from IAPWS-IF97 steam tables to produce engineering-grade sizing results. Water density at the feed temperature is used to convert mass flow to volumetric flow, while total head is calculated from drum pressure plus a 2.70 bar allowance for system friction and control valve losses. Shaft power is then derived from the hydraulic power equation adjusted for pump efficiency, and the recommended motor is the next standard IEC size above shaft power with a 15% safety margin applied. The engineering snapshot shows intermediate values — steam enthalpy, feed water enthalpy, water density, and thermal duty — so engineers can cross-check the results against boiler heat balance calculations. Results are returned in metric units regardless of input unit selection. This tool is intended for preliminary sizing only — final pump selection must be confirmed with vendor curves and a full NPSH analysis by a qualified engineer.
This boiler feed pump calculation tool supports both metric and imperial input units. Follow these four steps to get your sizing results instantly:
Step 1 — Select your unit system Toggle between Metric (kg/hr, °C, bar) and Imperial (lbs/hr, °F, psi) using the unit selector at the top of the calculator. All results are returned in metric units for engineering consistency regardless of the input unit selected.
Step 2 — Enter your boiler capacity Input the total steam output of the boiler in kg/hr (or lbs/hr in imperial mode). This is your rated evaporation rate — the mass of steam the boiler produces per hour under full load conditions. For boiler feedwater pump sizing calculation, always use the maximum continuous rating (MCR) rather than the normal operating load to ensure the pump can handle peak demand.
Step 3 — Enter feed water temperature, steam pressure, and pump efficiency The feed water temperature (°C) is the temperature of water entering the pump suction — typically measured at the deaerator outlet. Steam pressure (bar) is the drum pressure at which the boiler operates. Pump efficiency (%) is the hydraulic efficiency of the feed pump, typically between 65% and 85% for centrifugal pumps in this application. If you do not have a confirmed efficiency value, use 75% as a conservative starting estimate for preliminary boiler feed pump sizing calculation.
Step 4 — Read and interpret your results The Results panel instantly shows four key outputs: required flow rate, total head, shaft power required, and the recommended standard IEC motor size. The Engineering Snapshot below the results shows the intermediate values used in the calculation — steam enthalpy, feed water enthalpy, water density at the operating temperature, and the thermal duty reference for the boiler.
All formulas used in this boiler feed pump calculation tool are based on established thermodynamic and fluid mechanics principles used in industrial engineering practice.
The volumetric flow rate is calculated by dividing the mass flow of feed water by the density of water at the feed temperature:
Q (m³/hr) = ṁ (kg/hr) ÷ ρ (kg/m³)
Where:
Water density decreases significantly with temperature. At 20°C, density is approximately 998 kg/m³. At 105°C (a typical deaerator outlet temperature), density drops to approximately 954 kg/m³. Using an accurate density value is critical for correct boiler feed pump capacity calculation — an error here flows directly into every downstream result.
Total dynamic head is calculated from the differential pressure between the pump discharge and suction, plus a standard engineering safety allowance:
H (m) = [(P_steam + P_allowance) × 100,000] ÷ (ρ × g)
Where:
The boiler feed pump head calculation must account for both the drum pressure and the resistance of the feedwater system between the pump and the boiler drum. The 2.70 bar allowance used in this calculator is a standard conservative value for preliminary sizing — detailed system curve analysis may refine this for a specific plant layout.
Shaft power is calculated from the hydraulic power divided by the pump efficiency:
P (kW) = (ρ × g × Q × H) ÷ (3,600,000 × η)
Where:
Boiler feed pump efficiency calculation directly affects the motor size and operating energy cost. A pump running at 65% efficiency requires approximately 20% more power than the same pump at 78% efficiency. For long-running boiler plant applications, even a 2–3% improvement in pump efficiency can represent significant annual energy savings.
The recommended motor size is the next standard IEC frame motor above the calculated shaft power multiplied by a 1.15 safety margin:
P_motor = Next standard IEC size above (P_shaft × 1.15)
Standard IEC motor sizes used in this calculator: 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75, 90, 110, 132, 160, 200 kW.
Steam enthalpy (hg) at the boiler drum pressure is interpolated from standard saturated steam tables (IAPWS-IF97 standard):
Feed water enthalpy: hf (kJ/kg) = 4.186 × T_fw (°C)
Thermal duty: Q_th (kW) = ṁ (kg/hr) × (hg − hf) ÷ 3,600
The thermal duty reference shows the heat transfer rate required in the boiler — useful for cross-checking the boiler capacity against burner sizing and heat transfer surface area calculations.
Understanding the variables that affect a boiler feedwater pump sizing calculation prevents undersizing, oversizing, and costly operational problems.
Feed Water Temperature Has a Large Effect on Density and NPSH Feed water temperature is one of the most important variables in any boiler feed pump calculation. Higher temperature means lower density, which increases the required volumetric flow rate for the same mass flow. More critically, higher temperature means the water is closer to its boiling point, which reduces the Net Positive Suction Head Available (NPSHa) at the pump inlet. If NPSHa falls below the pump’s NPSHr (required), the pump will cavitate — causing severe mechanical damage within weeks of operation. Always specify the deaerator operating pressure and temperature to your pump vendor when ordering.
Operating Pressure Determines Total Head Boiler steam pressure is the dominant term in the boiler feed pump head calculation. A boiler operating at 60 bar requires roughly three times the pump head of one operating at 18 bar, with all other conditions equal. For high-pressure boilers above 40 bar, multi-stage centrifugal pumps are typically required since a single-stage pump cannot develop sufficient head economically.
Pump Efficiency Affects Energy Cost More Than Capital Cost Boiler feed pumps in continuous industrial operation run 7,000–8,000 hours per year. The boiler feed pump efficiency calculation directly determines annual electricity consumption. A 500 kW feed pump running at 72% efficiency instead of 80% efficiency wastes approximately 50 kW continuously — over 350,000 kWh per year at a significant energy cost. Always obtain pump efficiency curves from vendors and select the pump so that your normal operating point falls within 10% of the best efficiency point (BEP).
Boiler Capacity Must Include All Losses and Blowdown The boiler capacity value entered into this boiler feed pump capacity calculation should include continuous blowdown, steam used for soot blowing, and any other parasitic steam consumption, in addition to the useful steam output. A common industry practice is to add 5–10% to the net steam demand to account for these losses before performing the pump sizing calculation.
Always Size for Maximum Continuous Rating Boiler feed pumps must be capable of delivering at maximum continuous rating (MCR) under all credible operating conditions, including the highest possible steam pressure the drum safety valves will allow. Sizing against normal or average load will result in a pump that cannot maintain drum level during peak demand, boiler startup, or safety valve lift — potentially causing a boiler shutdown.
Number of Pumps — Duty and Standby Most boiler installations require a minimum of two feed pumps: one duty and one standby. For critical boilers in continuous process plant, two 100% duty pumps plus one standby is common. The standby pump must be capable of taking over immediately on duty pump failure. This boiler feed pump sizing calculation gives the sizing for one pump — verify your plant’s reliability requirements before selecting the number of units.
| Parameter | Typical Range | Notes |
|---|---|---|
| Boiler capacity | 500 – 200,000 kg/hr | Varies by application |
| Feed water temperature | 80°C – 140°C | Typically deaerator outlet |
| Steam pressure | 5 – 120 bar | Varies by boiler type |
| Pump efficiency | 65% – 85% | Centrifugal pump range |
| Head allowance | 2.0 – 3.5 bar | Depends on system layout |
| Motor safety margin | 10% – 20% | Applied above shaft power |
| NPSH margin | Min 0.5 m | NPSHa above NPSHr |
| Number of pumps | 2 – 3 | Duty + standby |
Everything you need to know about Boiler Feed Pump Calculator
