100+ Boiler Feed Pump Calculation: Formula, Sizing & Calculator

Boiler feed pump calculation is an important part of designing a reliable steam boiler system. The feed pump must supply enough water to the boiler at the correct flow rate and pressure while overcoming boiler pressure, pipe friction, elevation changes, valves, fittings, and other system losses.

If the boiler feed pump is too small, it may not maintain the required water level during high steam demand. On the other hand, an oversized pump can waste energy, create control problems, increase operating costs, and place unnecessary stress on the feedwater system.

A proper boiler feed pump calculation normally considers the boiler steam capacity, feedwater flow rate, operating pressure, total dynamic head, feedwater temperature, pump efficiency, NPSH, and motor power.

In simple terms, a boiler feed pump must satisfy two main requirements:

1. It must provide enough feedwater flow for the boiler.
2. It must produce enough pressure or head to push water into the boiler safely.

This guide explains the complete boiler feed pump sizing process, important formulas, calculation methods, practical design factors, and common mistakes engineers should avoid.

Boiler Feed Pump Calculation Calculator

A boiler feed pump calculator helps estimate the required pump flow rate, total head, discharge pressure, hydraulic power, and motor size.

For a basic boiler feed pump calculation, you usually need to know the boiler steam generation rate, boiler operating pressure, feedwater temperature, static elevation difference, pipe friction loss, and desired design margin.

The calculated values can then be compared with manufacturer pump curves to select a suitable boiler feedwater pump.

Boiler Feed Pump Calculator Input Parameters

The main input parameters used in boiler feed pump sizing include:

• Boiler steam capacity
• Boiler operating pressure
• Feedwater temperature
• Feedwater density
• Static head
• Suction pressure
• Pipe friction loss
• Valve and fitting losses
• Economizer pressure drop
• Control valve pressure drop
• Required safety margin
• Pump efficiency
• Motor efficiency

Not every boiler system will use exactly the same inputs. A small industrial boiler may require a relatively simple calculation, while a high-pressure boiler or power plant feedwater system requires a more detailed hydraulic analysis.

Boiler Feed Pump Calculator Results

A complete calculation can provide several useful results, including:

• Required feedwater flow rate
• Recommended pump capacity
• Required pump discharge pressure
• Total dynamic head
• Hydraulic pump power
• Shaft power
• Recommended motor power
• NPSH available
• Estimated pump operating point

These values provide the basic engineering information needed to choose a suitable boiler feed pump.

How to Use the Boiler Feed Pump Calculator

Start by entering the boiler steam generation capacity. This is normally given in kilograms per hour, tonnes per hour, pounds per hour, or another steam flow unit.

Next, enter the boiler operating pressure. The selected feed pump must produce a discharge pressure higher than the boiler pressure because additional pressure is needed to overcome piping losses, valves, fittings, elevation, economizer pressure drop, and other system resistance.

Then enter the feedwater temperature. Temperature is especially important when checking NPSH because hot water has a higher vapor pressure and is more likely to cavitate if the suction conditions are poor.

Finally, include the estimated system losses and pump efficiency. The calculator can then estimate the required flow, head, pressure, and power.

The calculated value should be treated as an engineering sizing reference. Final pump selection should also consider the actual pump curve, best efficiency point, NPSH requirement, operating range, and boiler manufacturer recommendations.

What Is a Boiler Feed Pump?

A boiler feed pump is a pump used to deliver feedwater into a steam boiler.

Inside the boiler, water is heated and converted into steam. As steam leaves the boiler, additional water must continuously enter the system to maintain the correct water level.

The boiler feed pump performs this job by taking water from a feedwater tank, condensate tank, hotwell, or deaerator and increasing its pressure enough to force it into the boiler.

Because a boiler operates under pressure, water cannot simply flow into it under normal atmospheric conditions. The feed pump must generate a pressure greater than the boiler operating pressure plus all other pressure losses in the feedwater system.

For this reason, boiler feed pumps are commonly high-pressure pumps, especially in industrial and power generation applications.

Purpose of a Boiler Feed Pump

The main purpose of a boiler feed pump is to maintain a reliable supply of water to the boiler.

As the boiler produces steam, the water level inside the boiler gradually decreases. The feedwater system replaces this lost water and keeps the boiler operating safely.

A properly selected boiler feed pump helps:

• Maintain the correct boiler water level
• Support continuous steam production
• Prevent low-water conditions
• Maintain stable boiler operation
• Overcome boiler operating pressure
• Compensate for feedwater system pressure losses
• Reduce the risk of boiler shutdown
• Improve overall system reliability

A feed pump therefore plays a direct role in both boiler safety and steam production.

How Boiler Feed Pumps Work

The boiler feed pump takes water from the feedwater source through its suction connection.

The pump impeller transfers mechanical energy to the water, increasing its pressure and velocity. In a multistage boiler feed pump, the water passes through several impellers arranged in series. Each stage increases the pressure further.

The pressurized feedwater then travels through the discharge piping toward the boiler.

Depending on the system, the water may pass through equipment such as:

• Feedwater control valves
• Economizers
• Check valves
• Flow meters
• Isolation valves
• Feedwater heaters

Each component creates some resistance to flow. The feed pump must therefore generate enough pressure to overcome the combined resistance of the entire system.

The basic operating relationship can be written as:

Required Pump Pressure = Boiler Pressure + Static Pressure + Friction Losses + Equipment Pressure Losses + Design Margin

This is one of the most important concepts in boiler feed pump calculation.

Boiler Feed Pump vs Boiler Circulation Pump

A boiler feed pump and a boiler circulation pump perform different functions.

A boiler feed pump supplies new feedwater to the boiler. It must normally operate at a discharge pressure higher than the boiler pressure.

A circulation pump, however, moves water through a closed or semi-closed heating circuit. Its main job is to overcome the pressure losses created by pipes, fittings, heat exchangers, and other components.

The circulation pump does not normally need to overcome the full boiler operating pressure because it is circulating water within an already pressurized system.

This distinction is important when selecting pumps because boiler feed pumps often require much higher pressure capabilities than standard circulation pumps.

Why Boiler Feed Pump Calculation Is Important

Boiler feed pump sizing should not be based only on the boiler connection size or a rough estimate of pump capacity.

A feed pump must work under specific flow, pressure, temperature, and operating conditions. If these conditions are not properly calculated, the selected pump may operate far away from its ideal performance range.

Correct boiler feed pump calculation helps ensure stable feedwater delivery while minimizing unnecessary energy consumption.

Maintaining Correct Boiler Water Level

The boiler water level must remain within a safe operating range.

When steam production increases, more water leaves the boiler in the form of steam. The feed pump must replace this water quickly enough to prevent the boiler level from falling too low.

If the feed pump cannot provide the required flow, the boiler may experience a low-water condition.

This can lead to alarms, burner shutdown, production interruptions, or serious equipment damage in extreme cases.

Preventing Pump Undersizing

An undersized boiler feed pump may provide enough water during light operating conditions but fail when the boiler reaches maximum steam demand.

For example, suppose a boiler normally operates at 60% load but occasionally reaches full capacity. A pump selected only for normal operation may not provide enough feedwater during peak demand.

Proper sizing should therefore consider the maximum expected boiler steaming rate rather than only average operating conditions.

Avoiding Excessive Pump Energy Consumption

Selecting a much larger pump than necessary may appear safe, but excessive oversizing creates its own problems.

An oversized pump may require the control valve to remain heavily throttled to reduce the flow. This wastes pressure as heat across the valve and increases energy consumption.

Oversizing can also cause the pump to operate far from its best efficiency point.

A correctly sized boiler feed pump should provide sufficient capacity and pressure while operating reasonably close to its efficient operating region.

Protecting the Boiler and Feedwater System

Stable feedwater pressure helps protect valves, piping, economizers, and boiler components.

Large pressure fluctuations can make feedwater control more difficult and may increase mechanical stress on the system.

Proper calculation also helps engineers check important operating conditions such as NPSH and minimum flow, reducing the risk of cavitation, overheating, and premature pump damage.

Key Parameters for Boiler Feed Pump Calculation

Several engineering parameters determine the final boiler feed pump size.

Understanding each parameter makes it easier to calculate the required pump capacity, pressure, total head, and motor power accurately.

Boiler Steam Generation Rate

The boiler steam generation rate represents the amount of steam produced over a specific period.

Common units include:

• kg/h
• t/h
• lb/h

This is one of the main starting points for boiler feed pump flow calculation.

If a boiler produces 10,000 kg/h of steam, the feedwater system must generally return approximately the same amount of water, with additional allowances depending on blowdown, operating conditions, and design margin.

Feedwater Flow Rate

Feedwater flow rate is the amount of water the pump must supply to the boiler.

A basic relationship is:

Feedwater Flow = Steam Production + Blowdown Requirement

A design margin may then be added to ensure the pump can handle maximum operating conditions.

For example, if the required boiler feedwater flow is 10 m³/h and a 20% design allowance is applied:

Required Pump Capacity = 10 × 1.20

Required Pump Capacity = 12 m³/h

The exact allowance should be selected according to the boiler design and operating philosophy rather than applying an unnecessarily large margin.

Boiler Operating Pressure

Boiler pressure has a major effect on feed pump sizing.

The pump discharge pressure must be higher than the pressure inside the boiler.

For example, if a boiler operates at 10 bar, selecting a pump that produces exactly 10 bar would normally be insufficient because pressure is also lost through pipes, fittings, control valves, economizers, and other components.

The required feed pump pressure may therefore be calculated as:

Pump Discharge Pressure = Boiler Pressure + System Pressure Losses + Static Pressure Requirement + Design Margin

Static Head

Static head is created by the vertical elevation difference between points in the feedwater system.

If the boiler feedwater inlet is located above the pump, the pump must provide additional head to lift the water.

Static head can be approximated by:

Static Head = Vertical Elevation Difference

For water systems, an elevation difference of 10 meters represents approximately 10 meters of static head.

The actual pressure equivalent depends on fluid density.

Friction Loss

Water flowing through pipes experiences resistance.

This resistance creates pressure loss, which the feed pump must overcome.

Friction losses depend on several factors, including:

• Pipe diameter
• Pipe length
• Water velocity
• Pipe material
• Number of bends
• Valves
• Tees
• Reducers
• Strainers
• Check valves
• Other fittings

Long or undersized feedwater piping can significantly increase the required pump head.

Required Pump Discharge Pressure

Required discharge pressure is the minimum pressure the pump must produce at its outlet to move feedwater into the boiler under the required operating conditions.

A simplified relationship is:

Required Discharge Pressure = Boiler Pressure + Total System Pressure Loss

For more accurate sizing, static head and equipment pressure drops should also be included separately.

Total Dynamic Head

Total dynamic head, commonly called TDH, represents the total head the pump must overcome while delivering the required flow.

A simplified boiler feed pump TDH equation is:

TDH = Static Head + Pressure Head + Friction Head + Equipment Losses

TDH is usually expressed in meters or feet of liquid.

Pump manufacturers commonly use flow rate and head rather than only pressure when presenting pump performance curves.

Feedwater Temperature

Feedwater temperature affects water density, vapor pressure, NPSH, and pump suction conditions.

Boiler feedwater is often hot because condensate is recovered from the steam system or because the water has been heated in a deaerator.

As water temperature rises, its vapor pressure also rises. This increases the risk of cavitation if the pressure at the pump suction becomes too low.

Feedwater temperature should therefore always be considered when checking NPSH.

Pump Efficiency

Pump efficiency represents how effectively the pump converts mechanical shaft power into useful hydraulic power.

No real pump operates at 100% efficiency.

The relationship can be expressed as:

Pump Shaft Power = Hydraulic Power ÷ Pump Efficiency

For example, if the hydraulic power requirement is 10 kW and the pump efficiency is 70%:

Pump Shaft Power = 10 ÷ 0.70

Pump Shaft Power = 14.29 kW

A motor must then be selected with sufficient capacity to drive the pump safely.

Motor Efficiency

The motor also has its own efficiency.

If electrical input power is being calculated, motor efficiency should be considered in addition to pump efficiency.

The approximate relationship is:

Electrical Input Power = Pump Shaft Power ÷ Motor Efficiency

Higher-efficiency motors can reduce energy consumption, especially for boiler feed pumps that operate continuously.

Safety Margin

A reasonable design margin helps the boiler feed pump handle operating variations.

However, the safety margin should not be excessive.

Adding very large margins to flow, head, and motor size can result in an oversized pump with poor energy performance.

The design margin should consider real factors such as expected load variation, future expansion, control requirements, and system uncertainty.

Boiler Feed Pump Flow Rate Calculation

Boiler feed pump flow rate calculation determines how much water the pump must deliver to the boiler during operation.

The required flow mainly depends on the boiler steam generation rate, blowdown losses, condensate recovery, and the design allowance used for the feedwater system.

A simple boiler feedwater flow calculation starts with the steam output because the water entering the boiler must replace the water leaving as steam.

Boiler Feedwater Flow Formula

A basic boiler feedwater flow formula is:

Feedwater Flow = Steam Flow + Blowdown Flow

If a design margin is required, the formula can be written as:

Required Pump Flow = Feedwater Flow × Design Factor

For example, if the calculated feedwater requirement is 8,000 kg/h and the design factor is 1.20:

Required Pump Flow = 8,000 × 1.20

Required Pump Flow = 9,600 kg/h

This means the selected boiler feed pump should be able to provide approximately 9,600 kg/h under the required discharge pressure and operating conditions.

Feedwater Flow Based on Steam Capacity

For a simple system, the boiler feedwater requirement is often close to the steam generation rate.

If a boiler produces:

5,000 kg/h of steam

and the blowdown requirement is:

250 kg/h

then:

Feedwater Requirement = 5,000 + 250

Feedwater Requirement = 5,250 kg/h

If a 15% design margin is added:

Pump Flow = 5,250 × 1.15

Pump Flow = 6,037.5 kg/h

The required pump capacity would therefore be approximately:

6,040 kg/h

This value can then be converted into volumetric flow such as m³/h or GPM depending on the pump manufacturer’s data.

Feedwater Flow With Safety Margin

A safety or design margin is commonly added because actual boiler demand can vary.

Possible reasons include:

• Changes in steam demand
• Boiler blowdown
• Feedwater control response
• Future load increases
• Measurement uncertainty
• Operating fluctuations

The design margin should be reasonable rather than excessive.

For example, if the calculated required flow is 12 m³/h and a 20% allowance is selected:

Pump Capacity = 12 × 1.20

Pump Capacity = 14.4 m³/h

This means a pump capable of delivering approximately 14.4 m³/h at the required head may be suitable.

Final selection should still be based on the actual pump curve.

Boiler Feed Pump Capacity Calculation

Boiler feed pump capacity is usually calculated from the maximum feedwater demand rather than the average demand.

A simplified formula is:

Pump Capacity = Maximum Feedwater Demand × Design Factor

Suppose:

• Maximum feedwater demand = 20 m³/h
• Design factor = 1.15

Then:

Pump Capacity = 20 × 1.15

Pump Capacity = 23 m³/h

This provides additional capacity for operating variations without creating excessive oversizing.

The pump must also be capable of producing the required head at this flow rate.

A pump rated for 23 m³/h is not automatically suitable if its discharge pressure is too low.

Flow and head must always be considered together.

Boiler Feed Pump Flow Rate in GPM

Many pump manufacturers use gallons per minute, especially in systems based on imperial units.

A useful conversion is:

1 m³/h ≈ 4.403 GPM

For example, if the required boiler feedwater flow is:

15 m³/h

then:

15 × 4.403 = 66.05 GPM

So the approximate pump flow requirement is:

66 GPM

If a safety margin is required, it should normally be added before final pump selection.

For example:

66 × 1.15 = 75.9 GPM

The selected pump may therefore need to provide approximately:

76 GPM

at the required head.

Boiler Feed Pump Flow Rate in m³/h

Metric systems commonly use cubic meters per hour.

If the mass flow rate is known, volumetric flow can be calculated using fluid density:

Volumetric Flow = Mass Flow ÷ Density

If the feedwater mass flow is:

10,000 kg/h

and the water density is approximately:

960 kg/m³

then:

Flow = 10,000 ÷ 960

Flow = 10.42 m³/h

This calculation becomes more important when feedwater temperature is high because hot water is less dense than cold water.

Using an incorrect density value can introduce error into the pump flow calculation.

Boiler Feed Pump Head Calculation

Boiler feed pump head calculation determines how much energy the pump must add to the feedwater to move it through the system and into the boiler.

Pump head is different from flow rate.

Flow tells us how much water the pump delivers.

Head tells us how much resistance the pump can overcome.

Both values are required when selecting a boiler feed pump.

What Is Pump Head?

Pump head is a way of expressing pressure in terms of the height of a liquid column.

It is commonly measured in:

• Meters of liquid
• Feet of liquid

For water, a pump that produces a greater head can overcome higher system pressure.

Pump head is useful because it allows pump performance to be compared without relying only on pressure units.

Boiler Feed Pump Head Formula

A simplified boiler feed pump head formula is:

Total Pump Head = Static Head + Pressure Head + Friction Head + Equipment Losses

In a more complete form:

TDH = Hs + Hp + Hf + He

Where:

• TDH = Total Dynamic Head
• Hs = Static Head
• Hp = Pressure Head
• Hf = Friction Head
• He = Equipment Loss Head

The final value represents the approximate total head the boiler feed pump must provide at the required flow rate.

Static Head Calculation

Static head is based on elevation difference.

If the boiler feedwater inlet is located 8 meters above the pump centerline:

Static Head = 8 m

If the pump is located above the feedwater source, suction static head may also need to be considered.

Static head does not normally change with flow rate unless the liquid levels in tanks or vessels change significantly during operation.

Friction Head Loss Calculation

Friction head loss is caused by water flowing through pipes and fittings.

It increases when:

• Flow rate increases
• Pipe diameter decreases
• Pipe length increases
• More fittings are installed
• Water velocity increases

Friction losses can occur in:

• Suction piping
• Discharge piping
• Elbows
• Tees
• Valves
• Strainers
• Check valves
• Flow meters
• Reducers

For example, suppose the total estimated piping friction loss is:

6 m

This value must be added to the other required head components.

Pressure Head Calculation

Pressure head represents the pressure the pump must overcome, especially boiler operating pressure.

For water, a useful approximate relationship is:

1 bar ≈ 10.2 m of water head

So if the boiler operating pressure is:

10 bar

the equivalent water head is approximately:

10 × 10.2 = 102 m

Therefore:

Pressure Head ≈ 102 m

This shows why boiler feed pumps often require high head even when the piping is relatively short.

Total Dynamic Head Calculation

Total dynamic head is calculated by adding all required head components.

Suppose a boiler feedwater system has:

• Boiler pressure head = 102 m
• Static head = 8 m
• Friction head = 6 m
• Control valve and equipment losses = 12 m

Then:

TDH = 102 + 8 + 6 + 12

TDH = 128 m

If a design allowance is added, the final pump head requirement may be slightly higher.

For example, with a 10% margin:

Design Head = 128 × 1.10

Design Head = 140.8 m

The selected pump should therefore be able to provide the required flow at approximately:

141 m head

This is one of the most important values used when checking a pump performance curve.

Boiler Feed Pump Pressure Calculation

Boiler feed pump pressure calculation determines the discharge pressure required to force feedwater into the boiler.

The feed pump discharge pressure must always be high enough to overcome boiler pressure and all additional system losses.

Required Boiler Feed Pump Discharge Pressure

A simplified calculation is:

Pump Discharge Pressure = Boiler Pressure + System Losses + Static Pressure + Control Margin

Suppose:

• Boiler pressure = 12 bar
• Friction losses = 0.8 bar
• Control valve loss = 1.2 bar
• Static pressure requirement = 0.5 bar
• Additional design margin = 1 bar

Then:

Pump Discharge Pressure = 12 + 0.8 + 1.2 + 0.5 + 1

Pump Discharge Pressure = 15.5 bar

The pump should therefore be capable of providing approximately:

15.5 bar discharge pressure

at the required flow rate.

Boiler Pressure vs Feed Pump Pressure

Boiler pressure and boiler feed pump discharge pressure are not the same.

This is a common mistake in pump sizing.

If a boiler operates at 10 bar, a pump rated to produce only 10 bar will generally not be enough.

The pump must also overcome:

• Piping friction
• Elevation
• Feedwater control valve losses
• Economizer pressure drop
• Check valve losses
• Other equipment losses

For this reason, feed pump pressure must normally be higher than boiler operating pressure.

Converting Pressure to Pump Head

Pump curves are often given in meters or feet of head rather than bar or PSI.

A common relationship is:

Head = Pressure ÷ Fluid Specific Weight

For practical water calculations, engineers often use approximate conversion factors.

For water:

1 bar ≈ 10.2 m head

Therefore, if the required discharge pressure is:

15 bar

then:

Head = 15 × 10.2

Head ≈ 153 m

This provides a quick way to compare the pressure requirement with a pump curve.

PSI to Feet of Head Conversion

For water, a commonly used approximation is:

1 PSI ≈ 2.31 ft of head

If the required pressure is:

150 PSI

then:

Head = 150 × 2.31

Head = 346.5 ft

So the pump must provide approximately:

347 ft of head

at the required feedwater flow rate.

Bar to Meter Head Conversion

For water:

1 bar ≈ 10.2 m head

For example:

18 bar × 10.2 = 183.6 m

So:

18 bar ≈ 184 m of water head

The exact value can vary slightly with water density and temperature, but this approximation is useful for preliminary boiler feed pump sizing.

Boiler Feed Pump Sizing Calculation

Boiler feed pump sizing combines flow, pressure, head, efficiency, and operating conditions into one complete selection process.

A reliable pump cannot be selected using only one parameter.

The pump must provide the required flow at the required head while operating within a suitable region of its performance curve.

Step 1: Determine Boiler Capacity

Start with the maximum steam generation capacity of the boiler.

For example:

Boiler Capacity = 10,000 kg/h

This value becomes the basis for estimating the feedwater requirement.

Step 2: Calculate Required Feedwater Flow

Add blowdown and any other expected water losses.

Suppose:

• Steam production = 10,000 kg/h
• Blowdown = 500 kg/h

Then:

Feedwater Requirement = 10,500 kg/h

If a 15% design allowance is used:

Pump Flow = 10,500 × 1.15

Pump Flow = 12,075 kg/h

Step 3: Determine Boiler Operating Pressure

Suppose the boiler operates at:

12 bar

The pump must produce a discharge pressure higher than this value.

Step 4: Calculate Static and Friction Head

Assume:

• Static head = 6 m
• Friction head = 9 m

These values must be added to the pressure head and other equipment losses.

Step 5: Calculate Total Dynamic Head

If the pressure head is approximately:

122.4 m

and the equipment losses are:

15 m

then:

TDH = 122.4 + 6 + 9 + 15

TDH = 152.4 m

Step 6: Add Design Safety Margin

If a 10% head margin is used:

Design Head = 152.4 × 1.10

Design Head = 167.64 m

The required pump should therefore deliver the calculated flow at approximately:

168 m head

Step 7: Select the Correct Pump

Now compare the required operating point with available pump curves.

The selected pump should provide:

• Required flow
• Required head
• Acceptable efficiency
• Suitable NPSH requirement
• Stable operating range
• Adequate material compatibility

Whenever possible, the operating point should be reasonably close to the pump’s best efficiency point.

Step 8: Check Motor Power Requirement

Once the pump flow and head are known, hydraulic and shaft power can be calculated.

The motor must be large enough to drive the pump under the maximum expected load without being unnecessarily oversized.

Motor selection should consider:

• Pump shaft power
• Pump efficiency
• Motor efficiency
• Service factor
• Maximum operating condition
• Starting requirements

This final check helps ensure the selected boiler feed pump can operate safely and continuously.

Boiler Feed Pump Formula

Boiler feed pump formulas help engineers calculate the flow rate, head, pressure, hydraulic power, shaft power, and motor requirement for a feedwater system.

There is no single formula that can describe every boiler feed pump system because the final selection depends on several operating conditions. However, a group of standard hydraulic formulas can be used together to determine the required pump duty.

Main Boiler Feed Pump Sizing Formula

A simplified boiler feed pump sizing relationship is:

Required Pump Duty = Required Flow at Required Total Dynamic Head

This means a pump should never be selected using flow alone or pressure alone.

For example, a pump rated for 20 m³/h may not be suitable if it can only produce 50 meters of head while the boiler system requires 150 meters.

The correct pump must provide both values at the same operating point.

Flow Rate Formula

If the feedwater mass flow and density are known, volumetric flow can be calculated as:

Q = m ÷ ρ

Where:

• Q = Volumetric flow rate
• m = Mass flow rate
• ρ = Fluid density

For example:

• Feedwater mass flow = 12,000 kg/h
• Water density = 960 kg/m³

Then:

Q = 12,000 ÷ 960

Q = 12.5 m³/h

This means the pump must deliver at least 12.5 m³/h before adding any required design allowance.

Total Head Formula

The total dynamic head formula can be written as:

TDH = Hs + Hp + Hf + He

Where:

• Hs = Static head
• Hp = Pressure head
• Hf = Friction head
• He = Equipment loss head

Suppose:

• Static head = 7 m
• Pressure head = 120 m
• Friction head = 8 m
• Equipment losses = 10 m

Then:

TDH = 7 + 120 + 8 + 10

TDH = 145 m

This means the selected boiler feed pump must provide the required flow at approximately 145 meters of total dynamic head.

Hydraulic Power Formula

Hydraulic power is the useful power transferred from the pump to the liquid.

The metric formula is:

Pₕ = ρ × g × Q × H

Where:

• Pₕ = Hydraulic power in watts
• ρ = Fluid density in kg/m³
• g = Gravitational acceleration, approximately 9.81 m/s²
• Q = Flow rate in m³/s
• H = Total head in meters

For power in kilowatts:

Pₕ(kW) = (ρ × g × Q × H) ÷ 1000

Flow must be converted from m³/h to m³/s before using this formula.

Pump Shaft Power Formula

The actual mechanical power required by the pump is greater than the hydraulic power because no pump is 100% efficient.

The formula is:

Pump Shaft Power = Hydraulic Power ÷ Pump Efficiency

If hydraulic power is 12 kW and pump efficiency is 75%:

Pump Shaft Power = 12 ÷ 0.75

Pump Shaft Power = 16 kW

This is the approximate mechanical power that must be supplied to the pump shaft.

Motor Power Formula

Motor power should be selected based on the required pump shaft power and the expected operating condition.

If electrical input power is being estimated:

Electrical Input Power = Pump Shaft Power ÷ Motor Efficiency

Suppose:

• Pump shaft power = 16 kW
• Motor efficiency = 92%

Then:

Electrical Input Power = 16 ÷ 0.92

Electrical Input Power ≈ 17.39 kW

The actual motor rating should then be chosen from a standard available motor size while considering service factor and maximum pump load.

Boiler Feed Pump Power Calculation

Boiler feed pump power calculation determines how much power is needed to move feedwater at the required flow and pressure.

The higher the flow rate and head, the greater the required pump power.

Pump efficiency also has a major influence on the final motor size.

Hydraulic Power Calculation

Consider a boiler feedwater system with:

• Flow rate = 20 m³/h
• Total head = 160 m
• Water density = 970 kg/m³

First convert flow to m³/s:

Q = 20 ÷ 3600

Q = 0.00556 m³/s

Now apply the hydraulic power formula:

Pₕ = ρ × g × Q × H

Pₕ = 970 × 9.81 × 0.00556 × 160

Pₕ ≈ 8,460 W

Therefore:

Hydraulic Power ≈ 8.46 kW

This is the useful power delivered to the water.

Pump Brake Horsepower Calculation

In imperial pump calculations, power may be expressed as brake horsepower.

A common water pump formula is:

BHP = (Q × H × SG) ÷ (3960 × η)

Where:

• BHP = Brake horsepower
• Q = Flow in GPM
• H = Head in feet
• SG = Specific gravity
• η = Pump efficiency as a decimal

Suppose:

• Flow = 80 GPM
• Head = 400 ft
• Specific gravity = 1.0
• Pump efficiency = 70%

Then:

BHP = (80 × 400 × 1.0) ÷ (3960 × 0.70)

BHP ≈ 11.54 HP

The selected motor must provide sufficient power above this requirement.

Motor Kilowatt Calculation

Motor power in kilowatts can be estimated using:

Motor kW = Hydraulic Power ÷ Pump Efficiency

If motor efficiency is also included for electrical input:

Electrical kW = Hydraulic Power ÷ (Pump Efficiency × Motor Efficiency)

Suppose:

• Hydraulic power = 9 kW
• Pump efficiency = 72%
• Motor efficiency = 90%

Then:

Electrical Power = 9 ÷ (0.72 × 0.90)

Electrical Power ≈ 13.89 kW

This means the electrical system must supply approximately 13.9 kW at this operating condition.

Effect of Pump Efficiency on Power

Pump efficiency has a direct effect on operating cost.

Two pumps can produce the same flow and head but consume different amounts of energy.

For example:

Pump A efficiency:

60%

Pump B efficiency:

80%

If both require 12 kW of hydraulic power:

Pump A shaft power:

12 ÷ 0.60 = 20 kW

Pump B shaft power:

12 ÷ 0.80 = 15 kW

Pump B requires 5 kW less shaft power for the same hydraulic duty.

This difference becomes significant for boiler feed pumps that operate for many hours each year.

Boiler Feed Pump NPSH Calculation

NPSH is one of the most important checks in boiler feed pump design because boiler feedwater is often hot.

NPSH stands for Net Positive Suction Head.

It describes how much pressure is available at the pump suction above the liquid vapor pressure.

If the available NPSH is too low, the water can begin to vaporize inside the pump. This can cause cavitation, vibration, noise, reduced performance, and damage to the impeller.

What Is NPSH?

NPSH is normally divided into two values:

• NPSH Available
• NPSH Required

NPSH Available is determined by the system.

NPSH Required is determined by the pump design and is normally provided by the pump manufacturer.

For safe operation:

NPSHA > NPSHR

A suitable margin should also be maintained rather than operating exactly at the minimum requirement.

NPSH Available Formula

A simplified NPSH available formula is:

NPSHA = Pressure Head at Liquid Surface + Static Suction Head – Suction Friction Loss – Vapor Pressure Head

For open tanks, atmospheric pressure may also be included.

For pressurized deaerators, vessel pressure has a major effect on NPSH available.

The exact calculation should match the actual suction arrangement.

NPSH Required

NPSH Required, or NPSHR, is the minimum suction head needed by the pump to achieve the specified performance without unacceptable cavitation.

This value changes with pump flow rate.

As the pump flow increases, NPSHR often increases as well.

That is why NPSH must be checked at the actual expected operating point and not just at one arbitrary flow rate.

NPSHA vs NPSHR

A pump may be considered unsuitable if:

NPSHA ≤ NPSHR

Even if the pump can provide the required flow and head, poor suction conditions can cause serious operating problems.

A good feedwater system should provide sufficient NPSH margin under the most difficult operating condition.

This is especially important when:

• Feedwater temperature is high
• Pump suction piping is long
• The feedwater tank is located close to pump level
• Suction pipe diameter is small
• Suction strainers create high pressure loss
• The pump operates at high flow

Effect of Feedwater Temperature on NPSH

Hot water has a higher vapor pressure than cold water.

As the feedwater temperature increases, the available margin before boiling becomes smaller.

For example, water at a high deaerator temperature is much closer to its boiling point than cold makeup water.

This means even a small pressure drop at the pump suction can cause local vapor formation.

For this reason, high-temperature boiler feed pumps are often installed below the deaerator or feedwater tank to create additional static suction head.

How to Prevent Cavitation in Boiler Feed Pumps

Cavitation can be reduced by improving suction conditions.

Practical methods include:

• Increase feedwater tank elevation
• Install the pump below the tank
• Increase suction pipe diameter
• Reduce suction pipe length
• Minimize bends and fittings
• Keep suction strainers clean
• Reduce unnecessary suction valves
• Avoid excessive pump flow
• Maintain adequate tank pressure
• Select a pump with lower NPSHR

The suction side of a boiler feed pump should be designed carefully because correcting NPSH problems after installation can be difficult and expensive.

Boiler Feed Pump Calculation Variables

A reliable boiler feed pump calculation depends on using the correct operating variables.

Each variable affects the final pump size in a different way.

Flow Rate

Flow rate represents the amount of feedwater supplied to the boiler.

It may be expressed as:

• kg/h
• t/h
• m³/h
• L/min
• GPM

Pump flow should normally be based on maximum expected boiler feedwater demand rather than only average operating conditions.

Pressure

Pressure represents the force required to push water into the boiler and through the feedwater system.

Common units include:

• bar
• kPa
• MPa
• PSI

The required discharge pressure should include boiler pressure and all relevant system losses.

Head

Head represents pressure in terms of a liquid column.

Common units are:

• meters
• feet

Pump manufacturers often use head on pump curves because it provides a convenient way to compare pump performance.

Water Density

Water density changes with temperature.

Cold water is denser than hot water.

Density affects:

• Mass-to-volume conversion
• Hydraulic power
• Pressure-to-head conversion

For more accurate boiler feed pump calculations, density should be based on the actual feedwater temperature.

Temperature

Feedwater temperature affects several important properties, including:

• Density
• Vapor pressure
• NPSH available
• Cavitation risk
• Pump material requirements

Temperature is particularly important in systems using deaerators or high levels of condensate return.

Pump Efficiency

Pump efficiency describes how much shaft power is converted into useful hydraulic power.

Efficiency changes across the pump performance curve.

A pump usually reaches its highest efficiency near its best efficiency point.

Operating too far away from this point can increase energy consumption and mechanical stress.

Motor Efficiency

Motor efficiency describes how much electrical input power is converted into mechanical shaft power.

Higher motor efficiency reduces electrical losses and operating costs.

The motor should also be large enough to handle the maximum expected pump load.

Pipe Diameter

Pipe diameter has a strong effect on friction loss.

A smaller pipe increases water velocity and usually increases friction head.

An excessively small discharge pipe can therefore increase the required pump head and energy consumption.

Suction pipe diameter is especially important because high suction losses reduce NPSH available.

Pipe Length

Longer piping creates more friction loss.

The effect becomes more significant at high flow velocity.

When calculating boiler feed pump head, the actual equivalent pipe length should ideally include fittings such as elbows, tees, valves, and reducers.

Boiler Feed Pump Calculation Example

A complete example makes the sizing process easier to understand.

Suppose an industrial steam boiler has the following operating data:

• Steam production = 15,000 kg/h
• Blowdown = 750 kg/h
• Feedwater density = 965 kg/m³
• Boiler operating pressure = 12 bar
• Static head = 8 m
• Piping friction loss = 10 m
• Equipment pressure loss = 15 m
• Pump efficiency = 75%
• Design flow margin = 15%

Example Input Data

First calculate total feedwater mass flow:

Feedwater Flow = Steam Flow + Blowdown

Feedwater Flow = 15,000 + 750

Feedwater Flow = 15,750 kg/h

Now add the 15% design margin:

Design Feedwater Flow = 15,750 × 1.15

Design Feedwater Flow = 18,112.5 kg/h

Step-by-Step Flow Rate Calculation

Convert the mass flow to volumetric flow:

Q = m ÷ ρ

Q = 18,112.5 ÷ 965

Q ≈ 18.77 m³/h

The pump should therefore provide approximately:

18.8 m³/h

at the required total dynamic head.

Step-by-Step Head Calculation

Convert the boiler pressure into approximate water head:

12 bar × 10.2 ≈ 122.4 m

Now add the remaining head components:

TDH = Pressure Head + Static Head + Friction Head + Equipment Losses

TDH = 122.4 + 8 + 10 + 15

TDH = 155.4 m

Therefore, the basic required pump duty is approximately:

18.8 m³/h at 155.4 m head

The final selection should then be checked against the manufacturer pump curve and applicable design margins.

Pump Power Calculation

Convert flow to m³/s:

Q = 18.77 ÷ 3600

Q ≈ 0.00521 m³/s

Now calculate hydraulic power:

Pₕ = ρ × g × Q × H

Pₕ = 965 × 9.81 × 0.00521 × 155.4

Pₕ ≈ 7.66 kW

Now account for 75% pump efficiency:

Pump Shaft Power = 7.66 ÷ 0.75

Pump Shaft Power ≈ 10.21 kW

The motor should be selected above this required shaft power after checking the full pump curve, maximum absorbed power, motor efficiency, and applicable service factor.

Final Pump Selection

Based on this simplified example, the target pump duty is approximately:

Flow: 18.8 m³/h

Head: 155 m

Pump Shaft Power: 10.2 kW

However, a pump should not be selected by choosing the nearest catalog number alone.

The final pump selection should also verify:

• Pump operating point
• Best efficiency point
• NPSH required
• Minimum continuous stable flow
• Maximum absorbed power
• Feedwater temperature
• Materials of construction
• Mechanical seal requirements
• Motor rating
• Control method

This final verification is what turns a basic boiler feed pump calculation into a reliable engineering selection.

Quick-Input Boiler Feed Pump Calculator Table

Before calculating boiler feed pump size, collect the main operating values of your boiler and feedwater system. The table below provides a simple quick-input format that can be used for preliminary pump sizing.

Input Parameter	Enter Your Value	Common Unit	What It Means
Boiler Steam Capacity	______	kg/h or t/h	Maximum amount of steam produced by the boiler
Boiler Operating Pressure	______	bar	Normal operating pressure inside the boiler
Blowdown Rate	______	% or kg/h	Water discharged from the boiler to control dissolved solids
Feedwater Temperature	______	°C	Temperature of water entering the feed pump
Feedwater Density	______	kg/m³	Density of feedwater at operating temperature
Static Head	______	m	Vertical elevation difference the pump must overcome
Suction Pressure	______	bar	Pressure available at the pump suction
Suction Pipe Loss	______	m	Friction loss before the pump inlet
Discharge Pipe Loss	______	m	Friction loss in the discharge piping
Economizer Pressure Drop	______	bar or m	Pressure loss through the economizer
Control Valve Pressure Drop	______	bar or m	Pressure required across the feedwater control valve
Other Equipment Losses	______	bar or m	Losses through valves, fittings, meters, and other equipment
Flow Design Margin	______	%	Additional flow capacity allowed for operating variation
Head Design Margin	______	%	Additional pump head allowed for system variation
Pump Efficiency	______	%	Estimated efficiency of the selected pump
Motor Efficiency	______	%	Efficiency of the pump motor

Quick Calculation Results

Once the input values are available, calculate the main boiler feed pump requirements below.

Calculation Result	Formula or Basis	Result Unit
Total Feedwater Requirement	Steam Flow + Blowdown Flow	kg/h
Design Feedwater Flow	Feedwater Requirement × Design Factor	kg/h
Volumetric Flow Rate	Mass Flow ÷ Feedwater Density	m³/h
Pressure Head	Boiler Pressure converted to liquid head	m
Total Dynamic Head	Pressure Head + Static Head + Friction + Equipment Losses	m
Design Pump Head	TDH × Head Design Factor	m
Hydraulic Power	ρ × g × Q × H	kW
Pump Shaft Power	Hydraulic Power ÷ Pump Efficiency	kW
Electrical Input Power	Shaft Power ÷ Motor Efficiency	kW
Recommended Pump Duty	Design Flow at Design Head	m³/h at m head

For example, if a boiler requires 12 m³/h of feedwater and the calculated total dynamic head is 150 m, the preliminary pump duty can be written as:

Boiler Feed Pump Duty = 12 m³/h at 150 m head

If a 15% flow margin and 10% head margin are applied:

Design Flow = 12 × 1.15 = 13.8 m³/h

Design Head = 150 × 1.10 = 165 m

The preliminary pump selection point would therefore be approximately:

13.8 m³/h at 165 m head

This quick-input table is useful for initial boiler feed pump calculations, but final pump selection should also verify the manufacturer’s pump curve, NPSH requirement, feedwater temperature, efficiency, allowable operating range, and maximum absorbed power.

Conclusion

Boiler feed pump calculation is not only about choosing a pump with enough flow. A reliable selection must consider boiler steam capacity, feedwater demand, operating pressure, total dynamic head, friction losses, feedwater temperature, NPSH, pump efficiency, and motor power.

The most important starting point is to calculate the required feedwater flow and then determine how much head the pump must produce to overcome boiler pressure and all system losses. After that, the calculated duty point should be checked against the actual pump performance curve.

A properly sized boiler feed pump helps maintain a stable boiler water level, supports continuous steam production, reduces the risk of cavitation, and avoids unnecessary energy consumption. Pumps that are too small may fail to meet peak demand, while heavily oversized pumps can create control problems and operate inefficiently.

For preliminary sizing, the boiler feed pump calculator and quick-input table can make the process much easier. However, final pump selection should always consider actual operating conditions, NPSH requirements, feedwater temperature, manufacturer pump curves, minimum flow limits, and the maximum absorbed power of the selected pump.

By combining accurate flow calculation, total dynamic head, pressure requirements, and power calculations, you can select a boiler feed pump that operates safely, efficiently, and reliably throughout the boiler system’s expected operating range.

FAQs

How do I size a boiler feedwater pump?

To size a boiler feedwater pump, first determine the maximum feedwater flow required by the boiler. Then calculate the total dynamic head needed to overcome boiler operating pressure, elevation, pipe friction, valves, fittings, economizer losses, and other system resistance. The final pump should provide the required flow at the calculated head while maintaining acceptable efficiency and sufficient NPSH.

What is the formula for boiler feed pump calculation?

There is no single formula for the complete calculation because boiler feed pump sizing involves both flow and head. A basic flow calculation is Feedwater Flow = Steam Flow + Blowdown Flow. Total dynamic head can be estimated using TDH = Pressure Head + Static Head + Friction Head + Equipment Losses. These values are then used together to determine the required pump duty.

How do you calculate boiler feed pump capacity?

Boiler feed pump capacity is generally based on the maximum feedwater demand of the boiler. Calculate the steam production rate, add blowdown and other expected water losses, and then apply an appropriate design allowance. For example, if the boiler requires 10 m³/h of feedwater and a 15% design margin is used, the design pump capacity becomes approximately 11.5 m³/h.

How do you calculate boiler feedwater flow rate?

A simple method is to add the boiler steam flow and blowdown flow. If mass flow is known and volumetric flow is required, use Volumetric Flow = Mass Flow ÷ Feedwater Density. Because water density changes with temperature, using the actual feedwater temperature can improve calculation accuracy.

How much larger should a boiler feed pump be than the required flow?

A boiler feed pump normally includes some additional capacity to handle operating variations, blowdown, load changes, and control requirements. The exact design margin depends on the boiler system and operating philosophy. Excessive oversizing should be avoided because it can increase throttling losses, energy consumption, and control problems.

How do you calculate boiler feed pump head?

Boiler feed pump head is calculated by adding all resistance that the pump must overcome. A common relationship is Total Dynamic Head = Boiler Pressure Head + Static Head + Friction Head + Equipment Losses. Pressure losses across economizers, control valves, check valves, and other feedwater equipment should also be considered.

What pressure should a boiler feed pump produce?

The feed pump must produce a discharge pressure greater than the pressure inside the boiler. It also needs enough additional pressure to overcome elevation, piping friction, valves, fittings, control equipment, and other pressure losses. Therefore, selecting a pump with discharge pressure equal only to boiler pressure is generally not sufficient.

What is total dynamic head in a boiler feed pump?

Total dynamic head, or TDH, represents the total resistance the pump must overcome while delivering the required feedwater flow. It includes pressure head, static elevation, piping friction, and pressure losses through system components. TDH is usually expressed in meters or feet of liquid and is one of the main values used when selecting a pump from a performance curve.

How do you convert boiler pressure into pump head?

For preliminary water calculations, 1 bar is approximately equal to 10.2 meters of water head. Therefore, a boiler operating at 10 bar represents roughly 102 meters of pressure head. Actual calculations may vary slightly because water density changes with temperature.

How do you calculate boiler feed pump power?

Hydraulic power can be calculated using P = ρ × g × Q × H, where ρ is fluid density, g is gravitational acceleration, Q is flow rate in m³/s, and H is total head in meters. Pump shaft power is then found by dividing hydraulic power by pump efficiency.

How do you calculate the motor size for a boiler feed pump?

First calculate the pump shaft power from the required flow, head, and pump efficiency. The motor must then be selected with enough capacity to handle the maximum absorbed pump power under expected operating conditions. Motor efficiency, service factor, starting requirements, and available standard motor sizes should also be considered.

What is NPSH in a boiler feed pump?

NPSH stands for Net Positive Suction Head. It is used to determine whether enough suction pressure is available to prevent feedwater from vaporizing inside the pump. Boiler feedwater is often hot, so NPSH is particularly important because higher water temperature increases vapor pressure and the risk of cavitation.

What is the difference between NPSHA and NPSHR?

NPSHA is the Net Positive Suction Head Available from the feedwater system, while NPSHR is the Net Positive Suction Head Required by the pump. For reliable operation, NPSHA should be greater than NPSHR with an appropriate margin.

Why is feedwater temperature important in boiler feed pump calculation?

Feedwater temperature affects water density, vapor pressure, NPSH, and cavitation risk. Hotter water has a higher vapor pressure, which makes it easier for the water to flash into vapor if suction pressure becomes too low. This is why feedwater temperature should be considered when designing the pump suction system.

What causes cavitation in a boiler feed pump?

Cavitation occurs when local pressure inside the pump falls below the vapor pressure of the feedwater. Common causes include high feedwater temperature, insufficient suction head, undersized suction piping, excessive suction friction, dirty strainers, or operating the pump at an excessively high flow rate.

How can boiler feed pump cavitation be prevented?

Cavitation can be reduced by increasing available suction head, installing the pump below the feedwater tank or deaerator, increasing suction pipe diameter, reducing suction friction losses, keeping strainers clean, and selecting a pump with an appropriate NPSH requirement.

Should a boiler feed pump be oversized?

A reasonable design allowance may be useful, but excessive oversizing should be avoided. An oversized pump can operate far from its best efficiency point, consume more energy, require heavy control-valve throttling, and experience increased mechanical stress. Pump selection should be based on realistic maximum flow and head requirements.

Why must boiler feed pump pressure be higher than boiler pressure?

Feedwater must move from the pump into a pressurized boiler. The pump therefore needs enough pressure not only to overcome boiler pressure but also to overcome pipe friction, elevation, valves, economizers, and other system resistance. This makes the required feed pump discharge pressure higher than the boiler operating pressure.

Which type of pump is commonly used as a boiler feed pump?

Multistage centrifugal pumps are commonly used for medium- and high-pressure boiler feedwater applications because multiple impeller stages can generate high discharge head efficiently. The actual pump type depends on required flow, pressure, temperature, NPSH, duty cycle, and installation arrangement.

What is the most important value when selecting a boiler feed pump?

There is no single value that should be considered alone. The main selection point is the required flow at the required total dynamic head. NPSH, feedwater temperature, pump efficiency, materials, operating range, and motor power must also be checked before making the final selection.

How do I know if my boiler feed pump is correctly sized?

A correctly sized pump should provide sufficient feedwater during maximum boiler demand, maintain stable discharge pressure, operate within an acceptable region of its pump curve, have adequate NPSH margin, and avoid excessive throttling or power consumption. Comparing the calculated system duty with the manufacturer’s performance curve is an important final step.