Boiler Feed Pump Calculator
Calculate boiler feed pump flow rate, TDH, pump power, NPSH, fluid velocity, density and viscosity. Default values are pre-loaded and the result below is calculated automatically — edit any field and click Calculate to update your boiler feed pump calculation.
Input Parameters
Results
Total Dynamic Head — Breakdown
Recommendations
How to Use This Boiler Feed Pump Calculator
Default values are already loaded and calculated — you can read the results immediately, or edit any field:
- Edit Flow Rate, Suction Pressure, Discharge Pressure, Elevation, Temperature, Pipe Diameter, Pump Efficiency, or NPSH Required as needed — every field already has a working default.
- Optionally enable Manual Property Override to enter your own density, viscosity, and vapor pressure instead of the temperature-based estimate.
- Optionally add suction/discharge friction losses, a motor sizing margin, or pipe length & roughness — all are safely ignored (treated as zero) if left blank.
- Optionally expand “Boiler Feedwater Sizing” and check “Use Boiler Feedwater Calculation” to size the pump from steam generation, blowdown and a safety factor instead of a direct flow rate.
- Click Calculate after any change, or just read the auto-calculated defaults. Copy, print, or download the results as a CSV at any time.
What Is Boiler Feed Pump Calculation?
Boiler feed pump calculation is the process of determining the flow, head, power and NPSH a feedwater pump must deliver. This calculator’s primary workflow needs only flow rate, suction and discharge pressure, temperature, pipe diameter, pump efficiency, NPSH required and elevation difference — every other field is optional and safely defaults to a value that does not distort the result.
Boiler Feed Pump Flow Rate Calculation
By default, the Flow Rate field drives every hydraulic result directly. If you enable Boiler Feedwater Calculation, feedwater flow instead replaces both the steam leaving the boiler and the water removed as blowdown:
Boiler Feed Pump Head / TDH Calculation
Friction losses default to zero and are only added when you supply them. Pressures entered as absolute are first converted to gauge (subtracting 1.01325 bar) so gauge and absolute values are never mixed.
Discharge Pressure and Suction Pressure
Discharge Pressure (also called boiler pressure) is the pressure at the pump’s destination side; Suction Pressure is the pressure at the pump inlet. Both default to gauge pressure, with a Gauge/Absolute selector for each. Pressure converts to head using the fluid density at the operating temperature:
Pipe Diameter and Fluid Velocity
As a preliminary screening guideline only, velocities above roughly 3 m/s in liquid feedwater lines may warrant a closer look at pipe sizing.
Feedwater Temperature, Density and Viscosity
Density, viscosity and vapor pressure are calculated automatically from temperature using a standard saturated-water property table (0-200°C, linear interpolation) — you never need to enter them manually. Fluid properties are approximate for preliminary engineering calculations; use actual process data, or the Manual Property Override, for final pump selection.
Boiler Feed Pump Power Calculation
Motor Sizing Margin defaults to 0%, so Recommended Motor Power equals Shaft/Input Power until you enter a margin.
Pump Efficiency
Pump efficiency is the ratio of hydraulic power delivered to the fluid to the mechanical shaft power supplied to the pump. Always use the value from the manufacturer’s pump performance curve at your actual duty point for a final design.
NPSH Available vs NPSH Required
NPSH Available (NPSHa) is calculated automatically from absolute suction pressure, vapor pressure at temperature, and suction friction (if supplied). NPSH Required (NPSHr) comes from the pump manufacturer’s curve.
This preliminary NPSHa calculation does not include the Elevation Difference term used in TDH; for systems with significant suction-side elevation, verify NPSHa independently against manufacturer data.
Boiler Feed Pump Sizing
Feed pump sizing combines flow and TDH into the required pump curve point, power results into motor sizing, fluid velocity into pipe-sizing checks, and the NPSH margin into a suction-condition check. A selection is reasonable on paper when NPSHa comfortably exceeds NPSHr, velocity sits within a sensible range, and the selected motor covers the calculated motor power.
Boiler Feed Pump Calculation Formula
| Quantity | Formula | Units |
|---|---|---|
| Feedwater Flow | Steam Flow ÷ (1 − Blowdown%/100) | kg/h |
| Pump Flow Capacity | Feedwater Flow × Safety Factor | kg/h → m³/h |
| Pressure Head | P × 100000 ÷ (ρ × 9.81) | m |
| TDH | Discharge Head − Suction Head − Elevation + Suction Friction + Discharge Friction | m |
| Pipe Velocity | Q[m³/s] ÷ (π D² / 4) | m/s |
| Hydraulic Power | ρ × 9.81 × Q[m³/s] × TDH ÷ 1000 | kW |
| Shaft Power | Hydraulic Power ÷ Efficiency | kW |
| Motor Power | Shaft Power × (1 + Margin%) | kW |
| NPSHa | Head(Pabs) − Suction Friction − Head(Pvap) | m |
| NPSH Margin | NPSHa − NPSHr | m |
Step-by-Step Boiler Feed Pump Calculation Example
This walks through the calculator’s own default values. Always verify against your actual system and a manufacturer’s pump curve.
| Flow rate | 100 m³/h |
| Suction pressure | 1 bar(g) |
| Discharge pressure | 30 bar(g) |
| Elevation difference | 5 m |
| Temperature | 90°C (density ≈ 965.3 kg/m³, viscosity ≈ 0.315 cP, vapor pressure ≈ 0.70 bar(a) — calculated) |
| Pipe diameter | 100 mm |
| Pump efficiency | 75% |
| NPSH required | 3 m |
Step 1 — Velocity: pipe area ≈ 0.00785 m² for 100 mm ID; Q ≈ 0.0278 m³/s → velocity ≈ 3.54 m/s.
Step 2 — TDH: discharge pressure head (30 bar) ≈ 316.8 m; suction pressure head (1 bar) ≈ 10.6
m; TDH ≈ (316.8 − 10.6) − 5 ≈ 301.2 m.
Step 3 — Power: hydraulic power ≈ (965.3×9.81×0.0278×301.2)/1000 ≈ 79.2 kW; shaft/pump power ≈
79.2 ÷ 0.75 ≈ 105.6 kW.
Step 4 — NPSH: absolute suction pressure head (1 + 1.01325 bar) ≈ 21.3 m; vapor pressure head
at 0.70 bar(a) ≈ 7.4 m; NPSHa ≈ 21.3 − 7.4 ≈ 13.9 m — above the 3 m NPSHr entered.
kW to HP Conversion
Frequently Asked Questions
What is a boiler feed pump?
A boiler feed pump moves treated feedwater from a feedwater tank or deaerator into the boiler at a pressure equal to or higher than the boiler’s operating pressure, replacing water converted to steam and lost as blowdown.
How do you calculate boiler feed pump flow rate?
Enter a direct flow rate for the main calculation, or enable Boiler Feedwater Calculation to derive flow from steam generation rate, blowdown, and a sizing safety factor.
What is discharge pressure?
Discharge pressure is the pressure at the pump’s destination side — typically the boiler operating pressure.
What is suction pressure?
Suction pressure is the pressure available at the pump inlet, entered here as gauge or absolute pressure.
How is TDH calculated?
TDH combines the discharge gauge pressure head minus the suction gauge pressure head, adjusted for elevation difference, plus any suction and discharge friction losses.
How do you calculate pump power?
Hydraulic power is found from flow, TDH and density, then divided by pump efficiency to get shaft/input power — the figure shown as “Pump Power.”
What is NPSH available?
NPSH Available (NPSHa) is what the system provides at the pump suction, calculated automatically from suction pressure, vapor pressure at temperature, and suction friction loss.
What is NPSH required?
NPSH Required (NPSHr) is the suction head margin a specific pump needs at a given flow, taken from the manufacturer’s performance curve.
Why does pipe diameter affect velocity?
For a given flow rate, a smaller pipe diameter forces the fluid through a smaller cross-sectional area, increasing velocity.
How does temperature affect fluid density?
Water density decreases as temperature rises; this calculator estimates density, viscosity and vapor pressure from temperature automatically.
How do you size a boiler feed pump?
Combine the calculated flow, TDH, power, velocity and NPSH margin with the manufacturer’s pump curve to confirm a suitable pump and motor selection.
Why does boiler blowdown affect feedwater flow?
Blowdown removes concentrated boiler water drawn from the same feedwater supply, so the pump must deliver enough extra flow to cover both the steam generated and the blowdown removed.
