boiler feed pump calculation

What is a boiler feed pump calculation?

A boiler feed pump calculation determines how much head and power a pump needs to deliver feedwater from a deaerator or feed tank into a boiler operating at pressure. If this calculation is inaccurate, the system can suffer from unstable drum level, high energy usage, cavitation risk, or premature pump failure.

In practical engineering, you are usually balancing three things: required flow, required pressure increase, and real-world efficiency. The calculator above is designed to make those relationships easy to evaluate quickly.

Key inputs you need

• Flow rate (m³/h): Amount of feedwater needed by the boiler at design load.
• Discharge pressure (bar g): Pressure the pump must overcome at boiler entry.
• Suction pressure (bar g): Pressure available at the pump inlet.
• Static head (m): Elevation difference between suction and discharge reference points.
• Friction losses (m): Pipe, valve, and fitting losses between suction and discharge.
• Specific gravity (SG): Relative density of feedwater at operating temperature.
• Pump and motor efficiencies (%): Convert hydraulic output to electrical input realistically.

Core formulas used

1) Differential pressure

Differential pressure is the pressure rise the pump must generate:

ΔP (bar) = P_discharge − P_suction

2) Pressure head and total dynamic head

Convert pressure difference to head and add static and friction components:

Pressure Head (m) = (ΔP × 10.197) / SG

TDH (m) = Pressure Head + Static Head + Friction Losses

3) Hydraulic and motor power

Hydraulic power is fluid work. Shaft and motor powers include efficiency losses.

P_hyd (kW) = ρ × g × Q × TDH / 1000

where ρ = 1000 × SG (kg/m³), g = 9.80665 m/s², and Q is flow in m³/s.

P_shaft = P_hyd / η_pump
P_motor = P_shaft / η_motor

Worked example

Using the default values in the calculator:

• Flow = 30 m³/h
• Discharge pressure = 40 bar g
• Suction pressure = 1.5 bar g
• Static head = 15 m
• Friction losses = 12 m
• SG = 0.96, Pump efficiency = 78%, Motor efficiency = 93%

The result is approximately:

• Differential pressure: 38.5 bar
• TDH: 436 m
• Hydraulic power: 34 kW
• Motor input power: 47 kW
• Recommended motor with 10% margin: about 52 kW

Common mistakes in boiler feed pump sizing

• Mixing gauge and absolute pressure: Keep pressure references consistent.
• Ignoring temperature effects: Hot feedwater density differs from cold water assumptions.
• Underestimating friction losses: Control valves and long runs can add major head loss.
• No power margin: Always include a realistic design/service margin.
• Focusing only on duty point: Check expected operation across minimum to maximum load.

Practical selection checklist

Hydraulic side

• Confirm normal and maximum boiler feed demand.
• Verify minimum continuous stable flow requirements.
• Include startup and transient conditions in the duty envelope.

Mechanical and electrical side

• Select a pump curve that places duty point near best efficiency region.
• Check NPSH available vs NPSH required with margin.
• Size motor for worst-case operating point and ambient conditions.

Final note

This calculator is ideal for quick engineering estimates and preliminary design checks. For final procurement, always validate against manufacturer pump curves, site piping isometrics, fluid properties at operating temperature, and your applicable code requirements.