Boiler Feed Pump Calculation

Convert the boiler's steam rate to water volume and apply a safety factor: gpm = steam lb/h / (8.337 × 60) × 1.5 for cold water. A 500 boiler horsepower boiler makes 17,250 lb/h of steam, so the pump flow is 51.7 gpm. The calculator also adjusts for feedwater temperature and blowdown.

Find three numbers: flow, pressure and power. Flow is the steam rate in volume plus a margin. Pressure is the relief valve setting plus 3% plus the piping drop. Power is flow times pressure divided by efficiency. For 500 boiler hp at 150 psig and 70% efficiency that is 51.7 gpm, about 159.5 psig and 6.9 shaft hp.

Work out the boiler's steam rate, convert it to feedwater flow with a safety factor, set the discharge pressure above the relief valve setting, add the head for height and piping, then choose a pump whose curve covers that duty with enough NPSH. The calculator does the flow, pressure and power steps.

Feed rate (gpm) = steam rate (lb/h) / (water density in lb per gallon x 60) x safety factor. With cold water at 8.337 lb per gallon that is steam lb/h / 500.2 x safety factor. A common rule of thumb for boilers rated in horsepower is about 0.1 gallon per minute per boiler horsepower at a 1.5 factor.

A boiler rating: one boiler horsepower is the energy needed to make 34.5 pounds of steam per hour at 0 psig and about 211 F with feedwater at the same temperature. It equals about 33,479 Btu per hour, or 9.81 kW. It is not mechanical horsepower and the two should not be mixed.

34.5 pounds per hour, which is about 15.65 kg per hour. The calculator takes boiler horsepower directly and converts it, so a 100 boiler hp boiler is 3,450 lb/h of steam. At 60 F water that needs about 6.9 gpm before the safety factor.

Common practice is 1.5 times the steam-rate flow, and some on-off control arrangements use 2 times so the pump refills quickly. The calculator starts at 1.5 and lets you change it. Your boiler maker, the pump supplier and the applicable code decide the final figure.

Water only flows into the boiler if the pump can push against the boiler pressure. Boiler practice asks for feedwater to be supplied at 3 percent above the relief valve setting, plus the pressure lost in piping and valves. At a 150 psig relief setting that is about 160 psig. The calculator applies the margin you enter, 3 percent by default.

Take the discharge pressure (relief setting x 1.03 plus piping drop), subtract any suction pressure, add pressure for height, and convert to feet of water at 2.31 feet per psi for cold water. At 150 psig relief with a 5 psi drop the discharge is 159.5 psig, about 368 feet of head.

Hydraulic horsepower = flow (gpm) x head (ft) x specific gravity / 3,960. Shaft horsepower is that divided by pump efficiency. For 51.7 gpm at 368 feet and 70% efficiency, hydraulic power is 4.81 hp and shaft power is 6.88 hp (5.13 kW).

Use the efficiency at the duty point from the pump maker's curve if you have it. Small boiler feed pumps are often well below the 70 percent a large pump can reach. The efficiency table shows that lowering it raises the shaft power in proportion, so a pessimistic value is the safer choice for motor sizing.

Yes, in two ways. Hot water is less dense, so the same mass flow is a larger volume: about 1.6 percent more at 140 F and about 4 percent more at 212 F than at 60 F. And hot water is close to boiling, which makes cavitation at the pump inlet a risk, so NPSH matters more. Enter the real temperature.

Net positive suction head is the pressure margin at the pump inlet above the point where the water would flash to vapour. If the available NPSH is too low the pump cavitates, which damages it and cuts flow. Feedwater is often hot, so check that the available NPSH exceeds what the pump needs by a safety margin. The calculator does not compute NPSH.

No. NPSH depends on the receiver level, the suction piping, the water temperature and the pump itself, and the pump maker gives the required value. Use the result here for flow, pressure and power, then check NPSH with the pump data. Many designers add a margin on top of the required value.

A common approach is to store about 10 minutes of the design flow. At 51.7 gpm that is about 517 gallons, and you would pick the next standard tank size up. The receiver size output multiplies the design flow by the storage time you enter.

Blowdown is water drained from the boiler to control dissolved solids. It has to be replaced, so the feedwater is the steam rate plus the blowdown. With 5 percent of the feedwater going to blowdown, the feedwater is steam / 0.95, which is about 5.3 percent more. Enter the share in the blowdown box.

Divide the mass flow by the water density to get volume: m3/h = kg/h / density. With 5,000 kg/h of steam, a 1.5 factor and water at 80 C (971.79 kg/m3) the pump flow is about 7.72 m3/h, or 34 gpm. The calculator accepts kg/h and returns both unit systems.

Yes. Choose metric, enter the steam rate in kg/h, pressures in bar gauge, heights in metres and temperature in degrees Celsius. The calculator returns flow in m3/h, discharge pressure in bar, head in metres and power in kW, and also shows the imperial equivalents.

Discharge pressure = relief valve setting x (1 + margin) + piping and valve pressure drop. With a 3 percent margin, a 150 psig relief setting and a 5 psi drop it is 150 × 1.03 + 5 = 159.5 psig, which is usually rounded to 160. In bar the same idea applies: 10.5 × 1.03 + 1.0 = 11.8 bar g.

Enter the vertical height from the pump to the boiler water level as the static height. It adds pressure equal to density x gravity x height, about 0.433 psi per foot for cold water, to the head the pump must produce. If the receiver sits above the pump, use the suction pressure box for the pressure it supplies.

It is the gauge pressure in the feedwater receiver or deaerator at the pump inlet. A vented receiver is 0 psig. A pressurised deaerator gives a positive value, which reduces the pressure rise the pump has to add. Leave it at 0 if you are unsure, since that gives a larger, safer pressure rise.

Take the shaft power from the calculator and choose a standard motor size above it, with a margin for the operating range and service factor. Your pump supplier will confirm the motor from the pump curve. The calculator gives shaft power in hp and kW so you can compare with motor ratings.

A condensate pump returns condensed steam to the feedwater receiver at low pressure. The boiler feed pump takes water from the receiver and pushes it into the boiler at boiler pressure, so it needs far more head. This calculator sizes the boiler feed pump, not the condensate pump.

A boiler needs a reliable water supply, and a failed pump can leave the boiler short of water. Many codes and designs therefore ask for more than one means of feeding the boiler, often two pumps each able to carry the full duty. Check the code that applies where you are.

A 500 boiler hp boiler at 150 psig relief setting: steam 17,250 lb/h, pump flow 51.7 gpm at 1.5 x, discharge 159.5 psig, head about 368 ft, hydraulic power 4.81 hp and shaft power 6.88 hp at 70% efficiency. Change any input to see how the numbers move.

The tables on this page cover the same ground: boiler horsepower to flow, steam rate to flow, relief setting to head, power for sample duties and receiver volumes. You can print the page, and the calculator works out your own numbers.

Some on-off feed arrangements size the pump at twice the steam rate so it can refill the boiler quickly between cycles. Modulating feed can use a lower factor such as 1.5. The calculator lets you enter either factor, and the safety factor table shows the effect.

No. It is a sizing estimate for flow, pressure, power and receiver volume. The actual pump comes from the manufacturer's curves, and the installation must follow the boiler maker's instructions and the applicable code. Have a qualified engineer confirm the design.

Feedwater is clean water with the density of water at the temperature you enter, up to 212 F. The relief valve setting is the pressure at the boiler, the pump takes suction at the pressure you enter, and the steam rate is steady. It does not model transients, control valves or economiser details beyond the piping drop you enter.

It is built for steam boilers, where the feedwater replaces the steam produced. A hot water heating boiler circulates a closed loop with little make-up, so the sizing method differs. Use the steam rate and relief setting of a steam boiler.

Convert to steam rate first. Divide the rating by the heat needed per pound of steam, roughly 970 Btu per pound for steam from and at 212 F, or use boiler horsepower at 33,479 Btu per hour each. Enter the resulting lb/h or boiler hp in the calculator.

The relief valve setting plus your margin and the piping drop, as a gauge pressure at the pump discharge. It does not include the effect of height, which is added separately to the total head. For a reading in bar, the calculator gives both psig and bar g.

Choose imperial or metric, enter the boiler capacity in steam rate or boiler horsepower, then the feedwater temperature, relief valve setting, piping drop, static height, pump efficiency and storage time. The results give flow, discharge pressure, head, pump power and receiver volume.