Boiler Feed Pump Sizing Calculator (Flow, Head & Motor Power)

A boiler feed pump must deliver feed water against the full boiler pressure with enough spare capacity to cover blowdown and peak steaming. This calculator sizes the pump for flow, total head and shaft/motor power from the steam output, working pressure and feedwater temperature.

Boiler feed pumps are normally sized at 1.5–2× the boiler evaporation rate so the boiler can be refilled quickly after blowdown and during peak demand, and the discharge pressure is set above the safety-valve set pressure plus the feed regulator drop. Feedwater is pumped hot (80–105 °C), so NPSH available must always be checked separately.

A 2,000 kg/h boiler at 10 barg, fed from an atmospheric tank at 90 °C, sized at 1.5× evaporation with a 20% pressure margin needs roughly 3.1 m³/h at about 131 m head — about a 1.5 kW shaft (1.8 kW motor).

How the Boiler Feed Pump Sizing Calculator Works

The calculator first converts the steam output to a feed-water mass flow using your capacity factor, then to a volumetric flow using the density of water at the feedwater temperature. The required head is the design discharge pressure (boiler pressure plus your safety margin) minus any pressurised feed-tank pressure, converted to metres of liquid, plus the static and friction allowance. Shaft power follows from the hydraulic power divided by pump efficiency, and the recommended motor adds a 15% margin.

Design Notes

• Set the discharge pressure above the boiler safety-valve set pressure — not just the working pressure — where codes require it.
• Check NPSH available separately; hot feedwater is close to its boiling point.
• For modulating feed control a lower capacity factor (1.25×) may be acceptable; for on/off level control use 1.5–2×.