Boosting Heat Transfer Efficiency: The Role of Hot Water Circulating Heating Systems

What do a canning factory and a building with radiators have in common? They both require a hot water circulating system. For our purposes, we include steam as hot water. A hot water circulation heating system is a closed loop delivering heat to locations far from the central boiler. How do they work, and who uses them?

This article will answer those questions. It will explore hot water circulating heating systems and their pivotal role in boosting heat transfer efficiency. Understanding these systems helps create an energy-efficient process or living space. 

A Brief History of Hot Water Circulating Heating System

Hot water systems have a rich history dating back centuries. The idea came from the Romans in approximately 350 BC. They used a dry air heating system, called a hypocaust, that circulated hot air under floors and inside walls for warmth. 

Modern hot water heating systems emerged in the 19th century using the same principle as a hypocaust. Early systems relied on gravity and natural convection but were inefficient and required careful design. The invention of the circulating pump in the late 19th century revolutionized water circulation efficiency and control. Advancements in technology and materials in the early 20th century, such as electric recirculation pumps and steel pipes, further enhanced these systems. 

Today, hot water circulating heating systems are staples in industrial process heating and residential and commercial buildings. 

What Industries and Applications Require Hot Water Recirculation?

Some of the industries and applications include:

  1. Residential Buildings: Residential recirculating hot water systems heat residential buildings, such as apartments, condominiums, and single-family homes.
  2. Hotels and Resorts: In the hospitality industry, these systems meet the high demand for hot water in hotels, resorts, and other accommodation facilities. 
  3. Commercial Buildings: Commercial buildings, including offices, restaurants, shopping malls, and hospitals, require water recirculation systems for a continuous heat and hot water supply. Hot water is necessary for handwashing, dishwashing, and heat.
  4. Industrial Processes: Manufacturing or production processes rely on recirculation systems. They help maintain consistent temperatures and improve efficiency in food processing plants, breweries, pharmaceutical facilities, and chemical plants.
  5. Swimming Pools and Spas: Swimming pools, spas, and recreational facilities use recirculation systems to maintain the desired water temperature, ensuring comfort for swimmers and bathers.
  6. Greenhouses: Circulating water heaters maintain optimal temperatures for plant growth throughout the indoor infrastructure. 
  7. Agricultural Applications: Agricultural hot water recirculation systems provide warmth in poultry houses and prevent freezing during crop irrigation.
  8. Aquaculture: Water recirculation for fish farms can include oxygenation, ultraviolet light or ozone disinfection, automatic pH regulation, heat exchange, and denitrification.

Hot water recirculation systems are essential wherever a continuous hot water supply is required to enhance comfort, improve efficiency, and support various processes.

What is Circulation Heating Technology?

The technical term for circulation heating technology is hydronic heating. It is a heating system that uses water or another thermal fluid as the medium for heat transfer. It operates through a network of pipes that circulate the heated fluid throughout the building or process to provide warmth. This system is often used with radiators, underfloor heating, or convection units to distribute heat to various areas. It is used in industry to provide constant heat to steam-jacketed kettles and other processes. 

The principle behind this technology lies in the circulation of hot water or fluid. A boiler or heat source warms the fluid that travels through the system of pipes, radiating heat as it moves. Once the fluid cools down, it returns to the heat source to reheat, thus creating a continuous loop of heating and reheating, distributing warmth evenly throughout a building or process.

How Does a Circulating Hot Water System Work?

The process begins at the boiler, where immersion heaters heat water to a high temperature. The hot water gets pumped through pipes, radiators, underfloor heating systems, or other heat exchangers.

For space heating, the heat transfers from the water to the radiator body, where the heat radiates into the room, warming the surrounding environment. As the water or steam cools down, it returns to the boiler to reheat, and the cycle begins.

The system runs on a closed loop, meaning the water is continuously circulated, reheated, and reused, making it a highly efficient heating method. Users can individually control the temperature of each room by using thermostatic valves on the radiators or zones in underfloor heating systems, which allows for optimal energy usage and comfort. It works the same way in industrial process heating systems.

Unlike forced air systems, circulating hot water systems deliver heat more evenly and quietly, with no dust circulation. Depending on the boiler, they can also run using various heat sources, including gas, oil, wood, solar, or electricity.

How does a hot water recirculation loop work?

A hot water recirculation loop works by continuously circulating hot water through the pipes in a system or building to ensure an immediate hot water supply when needed. The system includes a recirculating pump, which pushes the hot water from the heater to the fixtures, and a dedicated return line that brings the cooled water back to the heater for reheating. This loop system creates a constant flow, minimizing the wait time for hot water.

The Different Types of Hot Water Circulating Heating Systems

There are several systems, each with unique characteristics and applications. They include:

  1. Hydronic Radiant Heating Systems: These systems use hot water flowing through pipes or tubes installed beneath the floor, inside walls, or ceiling to provide heating. The advantages are even heat distribution and energy efficiency in residential and commercial buildings.
  2. Baseboard Radiators: Baseboard radiators consist of metal fins attached to a pipe. Hot water flows through the pipe, heating the fins and radiating heat into the room. They offer a compact and efficient heating solution in residential buildings.
  3. Steam Radiators: Steam radiators still operate in some buildings today. A boiler generates steam that circulates through a metal radiator, radiating heat into the room. 
  4. Fan Coil Units: Fan coil units combine a heating coil and a fan to circulate hot water and distribute heat throughout a room. They are often used in large commercial or industrial buildings and offer precise temperature control.
  5. Heat Exchangers: They transfer heat from one fluid to another without mixing fluids. They provide very stable, reliable temperatures for these processes.
  6. Solar Heating Systems: These systems use solar collectors to absorb sunlight and heat water or other fluid circulating through the building for heating purposes. These environmentally friendly systems provide significant energy savings.
  7. Geothermal Heating Systems: Geothermal heating systems utilize the earth’s constant temperature to heat a fluid in pipes that circulate in the ground and through the building. Highly efficient geothermal systems can provide both heating and cooling.

The system choice depends on the application, and whether it’s in new or existing construction. 

The Role of Hot Water Recirculating Systems in Heat Transfer Efficiency

Hot Water Recirculating Systems provide an uninterrupted flow of hot water. Here are its significant functions:

  • Improved energy efficiency: Hot water recirculating systems continuously circulate hot water through the pipes, thus reducing the amount of time and energy required to heat water when needed.
  • Quick access to hot water: These systems ensure immediate hot water at the fixtures.
  • Water conservation: Delivering immediate hot water eliminates the need to let water run while waiting for hot water to emerge from the tap or showerhead. 
  • Reduces energy waste: A thermostat, or aquastat, prevents the boiler from firing too frequently, ensuring the water remains within the set temperatures.
  • Pump control and efficiency requirements: Different code requirements exist for water circulation systems in different regions. The purpose is to efficiently control recirculating pump operation based on hot water demand and prevent the proliferation of bacteria in stagnant water.

One concern regarding hot water recirculating systems is bacterial growth in the pipes, specifically Legionella. The Centers for Disease Control reports that water temperatures between 77°F and 104°F (25°C and  40°C) are optimal for propagation of Legionella. Therefore, the system must retain temperatures above 104°F (40°C) to eliminate this threat.

Now that we understand its function let’s explore the critical system parts.

Components of a Recirculating Hot Water System

A recirculating hot water system typically consists of the following components:

  1. Pump: The recirculation pump is responsible for circulating the hot water through the system. It moves the water from the water heater to the desired fixtures and back to the heater again.
  2. Circulation Heaters: Circulation heaters are the heart of heat transfer systems. They heat the circulation fluid to the desired temperature.
  3. Check Valve: A check valve prevents the backflow of the water when the pump is not running. 
  4. Thermostat: The thermostat ensures a consistent water temperature in the system.
  5. Timer: It allows users to schedule when the recirculation pump operates. It saves energy by only running during periods of high demand.
  6. Return Line: The return line is a dedicated pipe that carries the cooled water back to the water heater from the fixtures. 
  7. Sensors: Some advanced recirculating systems may include sensors to monitor water temperature, flow rate, and pressure. These sensors help optimize the system’s performance and efficiency.
  8. Plumbing Connections: The system requires proper connections to connect the pump, check valve, thermostat, timer, and return line to the water heater and fixtures.

These components work together to maintain a continuous hot water supply throughout the system, minimizing wait times and conserving water.

Appropriate Sensor Placement for Optimal Heating

Proper circulation heater sensor placement plays a vital role in maximizing the efficiency of a hot water circulating heating system. Sensors monitor the water temperature, activating the circulation pump when the temperature drops below a preset level.

Strategic placement of sensors significantly enhances the system’s performance. For instance, placing a sensor near the furthest point from the water heater can ensure that hot water is readily available throughout the system. This placement can reduce the waiting time for hot water, conserve water, and improve the system’s efficiency.

Heat Exchange with Electric Heaters in Hydronic Heating Systems

Hydronic heating systems utilize hot water to heat a space. The systems use heat exchange with electric heaters.

The electric heater heats the water, and the hot water circulates throughout the system via pipes. The pipes can be embedded in flooring or attached to radiators or heated towel racks where the heat transfers from the water to the surrounding medium.

The cooled water returns to the heater for reheating. The closed loop ensures a continuous hot water supply and maintains the system’s efficiency.

What Are Some Benefits of Using Circulation Technology in Heat Transfer Systems?

The use of recirculating pumps and circulation technology offers numerous benefits:

  1. Energy Efficiency: Water holds more heat than air, keeping the space warmer longer than forced air systems for the same boiler run time.
  2. Reduced Water Wastage: It is a closed system, thus saving water.
  3. Cost Savings: Boilers can run on various fuels, including natural gas, oil, electricity, and wood. You can choose or convert to the least costly fuel for your area.
  4. Better Air Quality: No ductwork or fans blow air to heat the space. Clean heat radiates through the floor or from radiators.
  5. Extended Lifespan of Heating Systems: By reducing the stress on heating elements, circulation technology can extend the lifespan of heating systems.
  6. Lower Carbon Footprint: By using less energy, circulation technology helps reduce greenhouse gas emissions, contributing to environmental sustainability.

Is a hot water recirculation system worth it?

Yes, a hot water recirculation system is generally worth it. Sensors near the water fixtures trigger the pump to circulate more hot water if the temperature drops below the set point. A home recirculating pump costs approximately $200. A family of four can save around $50 to $75 per year by not wasting water waiting for hot water. If you wait 60 seconds for hot water to arrive at the tap or shower, that is a minimum of 1.5 gallons wasted in the shower and 2 gallons at the kitchen sink.

Multiply that by the number of times someone turns on hot water over a year, creating a tremendous amount of water wasted.

Maximizing Heat Transfer Efficiency with Circulation Technology In Various Applications

Circulation technology is critical in maximizing heat transfer efficiency in various applications, including:

  • Space heating – circulation technology ensures a uniform heat distribution, providing a comfortable environment. 
  • Hot water production – Provides an immediate hot water supply, reducing the waiting time and conserving water. 
  • Industrial process heating – Applications include jacketed vessels and tanks, heated rolls, heat exchangers, platens, dies, molds, and heat tracing.
  • Solar energy systems – Circulation technology circulates the water heated by the solar collectors throughout the system. 

Circulation technology provides a steady state or thermal balance throughout the system.

How Circulating Hot Water Heating Systems Reduce Energy Cost

Here are the various ways circulating hot water heating systems contribute to energy savings.

  1. Reduced Heat Loss: Traditional hot water systems experience significant heat loss as hot water sits in the pipes, losing heat to the surrounding environment. In contrast, circulating hot water systems keep the water in constant motion, limiting heat loss. The water reentering the circulation heater is at a higher temperature, requiring less energy to reheat.
  2. Minimized Water Waste: Waiting for hot water at taps and showers can waste up to 12 liters per user. With a circulating hot water system, hot water is readily available, eliminating the need to run the tap or shower until hot water arrives. 
  3. Improved Efficiency: Circulating hot water systems incorporate advanced components such as pumps, check valves, and aquastats. These components work together to optimize the system’s efficiency. 
  4. Customizable Scheduling: Many circulating hot water systems come equipped with timers, allowing users to schedule when the system operates. By programming the system to run during specific times of the day, users can ensure hot water is available when needed while minimizing energy consumption during idle periods. 

Now that we have explored how circulating hot water heating systems reduce energy costs, let’s find out the impact of water temperature drops and learn how to fix this common issue.

The Impact of Water Temperature Drops And How To Fix It

There are three primary reasons a heating system’s water temperature can drop. They are a lack of proper insulation, a malfunctioning aquastat or control system, and insufficient heat from an underpowered system.

To troubleshoot and fix water temperature drops in circulating hot water heating systems, take the following steps:

  1. Inspect the pipes, valves, and radiators for any signs of leakage or damage.
  2. Ensure that the insulation is intact and properly installed. 
  3. Verify that the thermostat is set to the desired temperature and functioning correctly. 
  4. Check the heating system, such as the boiler or furnace. Ensure the system is operating efficiently and clean or replace filters if necessary.
  5. Ensure that the water pressure is at the recommended level. Low water pressure can lead to a drop in temperature. 
  6. Air trapped in the radiators can prevent proper heat circulation. Use a radiator key to bleed any air pockets from the system. 
  7. Consider system expansion if it cannot meet the demand for hot water.

Schedule regular maintenance to prevent future temperature drops and to ensure optimal performance.

Circulating hot water is not the only method to heat buildings or processes.

How Does Circulation Technology Compare To Other Methods of Heat Transfer Such, As Radiation Or Conduction?

Closed-loop hot water circulating systems use circulation heaters to heat the water as it passes over heating elements. The heat in the water passes through the pipe walls or radiators. This form of heat exchange is convection. It offers advantages and disadvantages over the other two heat exchange methods, radiation and conduction. 

Here’s a table of the comparison.

Heat Transfer Method Advantages Disadvantages
(Circulation Technology)
Efficient and uniform heat distribution over larger distances, controllable for specific heating requirements. Heat transfer is faster. Requires energy input (a pump) to maintain fluid movement.
Conduction Directly transfers heat between objects in physical contact. No energy input is required for heat transfer. Limited to objects in direct contact, slower heat transfer compared to convection.
Radiation Heat transfer through electromagnetic waves can occur in a vacuum. No physical contact is required. No convection currents to move dust around the room. Less efficient over longer distances and limited control over heat distribution.


Convection heat transfer can be natural or forced. Natural convection happens as a heated fluid rises and sinks as it cools. Forced convection uses an external force, like a pump, to transfer heat from one medium to another.

Future Prospects of Circulation Technology In The Field of Heat Transfer

One of the most promising aspects of circulation technology is the ability to capture waste heat from industrial processes, power plants, and geothermal wells and use it to generate electricity. Circulating hot water systems are an excellent investment for residential, commercial, or industrial use that can significantly lower energy costs and contribute to a more sustainable future.

Powerblanket circulation heaters are the right choice for accurate process temperatures and increased efficiency. Explore Circulation Heaters today and experience the difference.

Powerblanket Circulation Heaters are the right choice for your process temperatures and increased efficiency.


Alex Pacanowsky

Meet Alex, one of our experts in freeze protection and the head of the custom team at Powerblanket! For the past several years, Alex has worked closely with oil & gas pros, medical device startups, and pharmaceutical suppliers (just to name a few) to create weatherproof operations. No matter how cold the weather, or what needs to be heated, Alex knows just what to do! He also loves mountain biking and spending time with his two boys, 5 and 9, and two Labrador Retrievers.

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