Boiler Feed Pump Calculation
Estimate boiler feedwater pump flow, required discharge pressure, total head, hydraulic horsepower, and motor horsepower from boiler load and system conditions.
How boiler feed pump flow is estimated
A common steam-boiler starting point is that one boiler horsepower produces about 34.5 lb/hr of steam. Feedwater gallons per minute can then be estimated by dividing steam mass flow by water density and minutes per hour, then applying a sizing factor for the control method.
McKenzie Corporation explains the common boiler-feed sizing equation using BHP × 34.5 ÷ 8.337 ÷ 60 × safety factor, while the pressure side still needs operating pressure, lift, friction, and margin.
Worked example
If the boiler operates at 100 psig and the piping losses plus margin require more pressure, the pump must be selected at both the required GPM and required head, not flow alone.
What this pump calculation does not include
NPSH is often the critical issue for hot feedwater. Deaerator pressure, receiver elevation, water temperature, suction pipe loss, flashing risk, minimum continuous flow, pump control method, and standby pump strategy all need engineering review.
Common questions
- A 1.5 factor is often used for intermittent on/off feed systems so the pump can recover level while the boiler is steaming. Continuous modulating feed systems may use a smaller factor, but the correct value depends on the control strategy and manufacturer requirements.
- They are linked by mass balance, but the units are different. The calculator converts steam lb/hr into gallons per minute using the approximate density of water, then applies the selected factor.
- It must overcome boiler operating pressure plus static lift, friction and control-valve losses, and a practical margin. The pump should be selected from its curve at the calculated flow and head.
- No. NPSH requires suction-side temperature, pressure, elevation, pipe losses, and vapor pressure. For hot feedwater, NPSH available can be the controlling pump selection factor.
- Use caution. Higher pressure and critical service boilers require more detailed pump selection, code compliance, materials review, redundancy, controls, and professional engineering.