What You Need To Know To Properly Size Boiler Feedwater Pumps

April 23rd, 2020

A Boiler Feedwater Pump is an essential component of a boiler system. Without it, feedwater from the tank cannot be transferred to the boiler. Depending on the operation requirements, boiler feedwater pumps control and regulate the input of the feedwater.

Now, getting a boiler pump is not as simple as ordering online or going into a store to buy one. Each boiler feed water pump is manufactured, engineered, and tailor-fitted to boiler operation.

Need some tips in selecting the boiler feed water pump? Here are 17 steps you need to know in choosing the best boiler feedwater pump.

A boiler’s operation can shut down if there is a low water condition. The capacity of the pumps to feed water into the system can determine the amount of water in the boiler at any given time. Properly sizing your boiler feedwater pumps can ensure smooth operation and longer boiler life.

Here’s what you need to know to properly size boiler feed water pumps:

  1. Fluid information

    Selecting your boiler pump starts with understanding the fluid that it will pump. Factors such as temperature, chemical composition, and viscosity are crucial information to consider when selecting your boiler feedwater pump.


    A boiler feed pump has a maximum temperature limit that it can handle. Depending on the fluid temperature, your boiler feed pump can be designed to meet the required needs.

    For the pumping of high-temperature fluids, the boiler feed pump must be equipped with auxiliary cooling. For example, for handling liquids above 220˚F (104˚C), water-cooled ball bearings should be added.

    The boiler feed pump can be damaged when there is an increase in the fluid’s temperature within a short period of time.

    Chemical composition

    Chemicals are sometimes added to the feedwater to produce a relatively pure vapor. Feedwater treatment can be done before it is transferred from the tank to the boiler feed pump. It can also be done either in the feed lines or within the boiler itself.

    External treatment is used when the feedwater has too many impurities to be tolerated by the boiler system. Removing or reducing these impurities must be done first before the feedwater passes through the deaerator and boiler feed pump.

    With internal treatment, treatments are added to the feedwater during the conditioning process. Some of the conditioning treatments added are:

    • Phosphates-dispersants
    • Polyphosphates-dispersants
    • Lignosulphonates
    • Tannins
    • Sodium sulfite
    • Hydrazine
    • Ascorbic acid derivatives

    Dissolved oxygen, carbon dioxide, and other materials can lead to corrosion of your boiler feed pump. Stripping the feedwater of these impurities can maintain your system’s product life.

    With this information, you can decide the size of the feed pipes. Aside from that, the materials (i.e., stainless steel, ductile iron, or cast iron) used for the construction of your boiler feed pump matter depending on those chemical additives.


  2. Pump Capacity & Pressure / Head Required

    A boiler feedwater pump’s capacity describes its flow rate. Calculate the minimum flow and maximum flow of your operation. Determining these factors can help you size your pump.

    Pump experts need to know how much flow rate and head are required for your operation. In turn, they will recommend the size of the impeller for your boiler pump since it is dependent on the pump capacity.

    Multiple impellers in a series build a multistage centrifugal pump. As the feedwater passes through each impeller (or stage), it gains velocity and pressure until it’s released in the discharge pipe. Some applications that require high head are power generation, boiler feed, and washdown services.

    The number of impellers is determined by the amount of head the operation requires. The higher the amount of head needed, the more stages the boiler feed pump should have. Knowing the required head for your operations can help determine the size of the pump.

    When you start calculating for the capacity and head of your operation, you can start creating a system curve. Sharing this system curve with your pump manufacturer will make it easier for them to recommend a pump size.

  3. Net Positive Suction Head

    The Net Positive Suction Head (NPSH) measures how much pressure is at the suction nozzle of the pump. There are two types of NPSH to consider: the NPSHa (Available) and NPSHr (Required).

    The NPSHa or Net Positive Suction Head Available is a measure of how much pressure on the pump to deliver the fluid. The NPSHr or Net Positive Suction Head Required is a measure of how much pressure is needed to keep the pump from cavitating.

    Suction Piping diameter and design highly affect the NPSH. The wrong size or design can lead to the poor performance of the boiler pump and its failure.

    Increasing the suction piping diameter will increase the NPSHa, and vice versa. The size of the piping diameter relates to the NPSHa, which includes the suction lift and pipe friction losses.

    Aside from a larger piping diameter, the design of the suction piping also affects NPSH. A design with a lot of valves, fittings, and elbows will result in higher friction losses. As a tip, straight pipes with minimal valves and fittings as possible.


    Image Source: xresch from Pixabay.

  4. Information on the Site and the Boiler Feed Pump’s Utility

    When you set the size of the boiler pump, the installation site should be a factor. Boiler feed pumps need regular inspection and maintenance. There should be enough space and headroom to perform these tasks. In addition, the area should be a dry location with adequate drainage.

    The area should also accommodate the correct installation of the pipework. There shouldn’t be excess stress or strains on all of the components and parts of the entire system. The piping connections should be independently supported.

    So, you must communicate your proposed installation site with your pump expert. They can guide and help you in properly size your boiler feed pump based on this information.

    Another factor that pump experts need to know is the purpose of your boiler operation. Depending on the purpose, you can determine the following pump size factors:

    • Flow Rate
    • Total Dynamic Head
    • NPSHa & NPSHr
    • Temperature

    Plus, the purpose and area size of your operation can help determine whether you need a vertical boiler feed pump or a horizontal boiler feed pump.

    If you need a smaller installation footprint, you can choose a vertical in-line pump. Horizontal centrifugal pumps take up more space.


  5. Other specifications

    Sharing other specifications to your pump manufacturer can help them tailor-fit the pump that you need for your boiler system. Below are some questions to consider when properly sizing your boiler feed pump:

    • Do you need special materials for your pumps and components?
    • How will the pump be operated? How often do you need to open or close valves?
    • What standards or certifications are required for your pump (i.e., ANSI, API, Quality Certifications)?
    • What type of coupling do you need?
    • How many pumps do you need for the entire operation?

    There are many considerations when you are choosing your boiler pump. To know more about boiler feed pumps, read the 7 Facts About Boiler Feed Pumps And How Finding The Right One Can Ensure Efficiency For Your Boiler System.

Determine All Necessary Information Before Talking To Your Pump Manufacturer

Gathering all these pieces of information for your operation can help you properly size your boiler feedwater pump.

  1. Fluid or Feedwater Information
  2. Pump Capacity & Pressure / Head Required
  3. Net Positive Suction Head Available
  4. Information on the Site and Purpose of the Pump
  5. Other Specifications (i.e., Special Materials Needed, Number of Pumps, Quality Standards, etc.)

Create a system curve based on the calculations of the pump capacity and pressure/head required. Talks with your pump manufacturer will go well when you share this data. Additionally, your pump manufacturer can provide more input and better insights to tailor-fit the pump that you need.

Talk To A Trusted Pump Manufacturer With Years Of Experience

Beyond properly sizing your boiler feed pump, choosing the right pump manufacturer can guarantee success with any pump application.

Carver Pump has been in the industry for more than 80 years. Their products have been used in different applications across many industries. They have the technical know-how to provide you with insights on which type and size of pumps you need for any steam boiler operation.

You can use the Pump Selection Tool. Simply register to get an account. Once done, you can enter the data, and you’ll get what kind of pump you need.


Simply input the flow rate, total head, and static head in the fields. If you have other information, input them, too. After you’ve entered all the data, it will return with the list of pumps that fits. You can select the size and curves of the pump you need.


The pump selection tool does not have a material selection. So, when you start discussing your boiler feed pump needs with your pump expert, make sure to talk about it.

At Carver Pump, you can choose between the RS and the RSV for your boiler feed needs.


The RS used in the State of California Department of General Services.


Two Carver Pumps RS-D size 6x3x8 4-stage pumps will feed an auxiliary boiler in a combined-cycle power plant in Pennsylvania, a clean-burning and natural gas-fueled electric generating station with a stated capacity of 925 megawatts of power.

The RS is a horizontal multistage ring section pump. It can handle moderate to high-pressure pumping suitable for heavy-duty industrial applications. Its hydraulic performance can reach flows of up to 2,000 GPM and heads to 3,400 ft. TDH. The RS comes in seven basic sizes and can be built up to 18 stages.

Aside from boiler feed applications, the RS is best used for:

  • Large vehicle washers
  • Irrigation systems
  • Light hydrocarbon transfer
  • Caustic and Chemical Feed
  • Coating, Surface, and Spray Paint Systems
  • Desalination and Reverse Osmosis
  • NOx Water Treatment
  • Paper Mill Shower Water
  • Sanitary Washdown Services
  • Ultra-high Purity Water Wash Systems
  • Wastewater Treatment Systems
  • High Rise Building Sprinklers
  • Ethane and Polyurethane
  • Hot Oil Applications


The RSV is Carver Pump’s in-line vertical multistage pump. It’s highly adaptable to various systems in a wide range of applications. Choose between its nine sizes and can be built up to 18 stages.

You can use the RSV for:

  • Boiler Feed Applications
  • Circulation
  • Desalination and Reverse Osmosis
  • Filtration
  • High Rise Building Sprinkler Systems
  • High Rise Building Water Pressure
  • Hot & Cold Water Systems
  • Jockey Pump Systems
  • Washing Systems
  • Water Supply Systems
  • Water Treatment Plants

Carver Pump’s quality management system is certified by Intertek to conform to ISO 9001:2015.  Our commitment to quality includes not only our hardware, but also superior customer service, leading-edge R&D, and continuous improvement in everything we do.

Check out Carver Pumps’ list of products to find one that suits your needs. Better yet, consult with a pump expert today.


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