Frequently Asked Questions

Heat transfer technology is a complex subject and here you will find some of the questions that are most frequently asked about heat exchangers and oil coolers, in terms of performance, design and operation.

We hope you find the answer to your question in the list below. However, if it’s not there, you can also click through to our Contact Us page, complete and send the enquiry form and we will respond directly with an answer to your particular question.

A heat exchanger is a device for transferring heat energy from a liquid or gas, to another liquid or gas without the two ever coming into contact with each other. A typical shell and tube heat exchanger will contain a tube bundle inside an outer shell, or body. Cold water flows through these tubes, whilst hot water, or gas flows around the outside of the tubes, enabling the heat from the hot water or gas to be transferred to the colder water inside the tubes.

A good example of how the process works are swimming pools, where most are heated via a boiler, using Gas, LPG or Biomass as the energy source. In theory, the most efficient way to heat the pool would be to circulate the pool water directly through the boiler. But were this to happen, the chemicals used in the pool water to keep it safe for use, would quickly corrode and damage vital parts inside the boiler, leading to premature failure and a costly replacement.

However, by using a heat exchanger to act as an ‘interface’ between the boiler water circuit and the pool water circuit, the boiler is protected from damage and the pool water is quickly heated up to the required temperature; the pool water passing through the central ‘tube core’, whilst the hot boiler water circulates around the outside of the tubes, transferring heat energy to the pool water.

More examples of applications where Bowman heat exchangers are used.

Mechanical equipment, such as internal combustion engines, gearboxes and transmission systems rely on oil to lubricate moving internal components, enabling them to run freely, whilst reducing wear to metallic surfaces.

In addition to lubrication, engine oil also acts as a coolant, to remove surplus heat from mechanical equipment. For example, a hot engine transfers heat to the oil, which then circulates through a heat exchanger (also known as an oil cooler), using either air or water to cool the oil.

All oils have a recommended operating temperature range and if this is exceeded, the viscosity of the oil can be weakened, reducing its lubrication qualities. Should excessive heat continue to build up, the oil’s ability to lubricate components will be significantly reduced and in extreme cases, the viscosity may break down, creating conditions where the metal components overheat, leading to premature wear. In extreme cases this could even result in a catastrophic component failure.

This situation can occur where equipment is to be operated at high speeds for extended periods, or where climatic conditions dictate higher ambient air temperatures. In such conditions, adding an oil cooler to the lubrication system, will remove the excess heat, reducing the oil’s temperature so that it remains within the correct range to protect the equipment, prolonging its operating life.

Whether an air or water cooled oil cooler is used depends on application and operating conditions.

Bowman oil coolers are water cooled ‘shell and tube designed units that are robust and reliable over a wide range of operating conditions. For more information about Bowman Oil Coolers.

An oil cooler is designed to remove excessive heat from the oil used to lubricate vehicles, machinery, and mechanical equipment. These types of coolers can be either a water-to-oil or air to oil type of heat exchanger.

Lubricating oils are developed for differing kinds of temperature ranges and operating conditions. To ensure an oil protects the machinery or equipment for which it was designed, it should always operate within its designated temperature range.

Too cold and it thickens, making it more difficult for the oil to lubricate the moving parts. Too hot and the viscosity of the oil could start to breakdown, resulting in premature component wear and ultimately equipment failure.

The problem is that moving metal parts generate lots of heat, which gets transferred to the lubricating oil. By adding an oil cooler into the lubrication circuit, the oil temperature is controlled and always kept within the correct operating range.

Oil coolers can be either air cooled or water cooled, depending on the nature of the application. Bowman manufacture a wide range of water cooled ‘shell and tube’ design oil coolers for off/on highway vehicles, construction plant and associated equipment, cooling heavy duty applications such as torque converters, automatic transmission and engine oils.

Find out more about Bowman oil coolers.


An oil cooler  is designed to remove excessive heat from the oil used to lubricate vehicles, machinery and mechanical equipment. For example, a hot engine transfers heat to the oil which then circulates through a heat-exchanger (also known as an oil cooler), using either air or water to cool the oil.

It achieves this by using a cooling medium – usually either air or water – to transfer heat from the oil and to the cooling medium. It does this without either the oil or cooling medium coming into direct contact with each other.

For example, an air cooled oil cooler often looks like a small car radiator and achieves its purpose by running the oil through finned tubes. The incoming air passes over and around the tubes, removing heat as it passes through.

For many applications, air cooling isn’t appropriate and here water cooling is the solution. Shell and tube oil coolers are very popular, the coolant flowing through the central ‘tube core’, whilst the oil flows around and through the tubes, providing extremely efficient heat transfer.

Bowman manufacture a wide range of water cooled shell and tube oil coolers for torque converters, automatic transmission and engine oils. Find out more about Bowman Oil Coolers.

In certain conditions where there is a significant temperature differential between the cooling medium and liquid being cooled, a shell and tube heat exchanger is often the more cost-effective cooling solution compared to a plate heat exchanger. This is due to the small flow path within the plate heat exchanger which creates significant amounts of turbulence, leading to high pressure drop within the unit.

As the name suggests, plate heat exchangers are constructed from a series of thin metal plates. Usually made in stainless steel, each plate contains an intricate pressed pattern, and to ensure the unit is watertight, rubber gaskets are ‘sandwiched’ between all the metal plates, which are then compressed together in a rigid frame to form an arrangement of parallel flow channels with alternating hot and cold fluids.

In contrast, shell and tube design heat exchangers consist of two primary components; the outer body (or shell) and tube core (or bundle) inside the shell. Cooling media flows through the tube core, whilst the hot fluid enters the shell via an inlet port, flowing through and around the outside of the tube core through a series of baffle plates, before leaving the shell via outlet port. For maximum heat transfer efficiency the hot and cold fluids travel in a ‘counterflow’ direction through the heat exchanger. For more information on counterflow.

Whilst plate heat exchangers can be quite compact and have the ability to be increased in size, should cooling requirements change, they will be more costly to maintain than the equivalent shell and tube heat exchanger, as typically the rubber gaskets age, harden and need replacing every 2 years. This is a time-consuming and costly exercise, putting the heat exchanger out of service for longer periods. Additionally, leak detection can be more difficult and requires skilled labour to undertake the work. And, due to greater water flow resistance inside the heat exchanger, there is an increased chance of fouling, reducing the efficiency of the unit.

In contrast, shell & tube heat exchangers are extremely easy to maintain; removing the end covers reveals the tube core, which can be withdrawn for cleaning and routine maintenance. Heat transfer efficiency of a quality shell & tube heat exchanger, such as Bowman, is extremely good, whilst the units themselves are tough, providing long life durability. Shell and tube heat exchangers can also be used with the most demanding cooling media, including sea water and mineral rich or contaminated water.

More information on Bowman’s range of shell & tube heat exchangers.


If your pool isn’t heating up to the required temperature, there are a few possible causes. Using this checklist could help you locate the problem:

1: Do I have enough energy?
Whether heating your pool with a gas boiler, solar panels, a heat pump, or another energy source, it is important you have enough energy to do the job.

2: Do I have the right heat exchanger?
A common misconception is the larger the heat exchanger, the faster it heats the pool! However, this isn’t necessarily the case. There are many types of heat exchanger used to heat swimming pools and they differ dramatically in design, performance and heat transfer efficiency.

3: My heating system is adequate but my pool still fails to heat up!
Flow rates of both the hot and cold fluids are vital for the heat exchanger to transfer thermal energy to the pool. If the hot water flow rate is too low, the available energy will not be passed through the heat exchanger. However, the flow rate of the pool water is equally important.

4: And if you’ve done all that…
Even if all the equipment is adequately sized, there may still be other parts of the system creating issues that will need to be checked.

5: In summary…
This is a summary of a more detailed article designed to help identify problems with pool heating and heat exchangers. Read the complete article here.

More product information on Bowman swimming pool heat exchangers.

Most hot tubs are supplied with an integral electric water heater, which are usually around 3 kW output, depending on the capacity of the hot tub. This type of heater will usually increase the water temperature by around 1 – 2 °C per hour, so it can take up to 24 hours to heat a tub using ambient temperature water.

To overcome this problem, some users fill their tub with pre-heated (25 °C) water from an adjacent boiler, but given that hot tubs usually operate at around 38-40 °C, it can still take a further 6 to 10 hours to achieve full temperature, depending on the performance of the electric heater.

This long heat up time has created a high level of dissatisfaction for many owners, who want their hot tubs to be available for use much faster than the standard heating system allows.

Consequently, many hot tub users, especially those in the commercial sector, are switching to a new type of heating system, using an external boiler, linked to a Bowman heat exchanger. The benefits include significantly reduced heat up times – typically 3 – 4 hours using ambient temperature water, or 1 hour using pre-heated water), plus significantly reduced energy costs compared to electric heating.

More information on heating hot tubs with Bowman heat exchangers.

Most hot tubs are supplied with an integral electric heater, usually around 3 kW output, depending on the water capacity. However, more recently, there has been a growing trend to use gas heating via an external boiler as this is faster at heating up the water compared to electric. This means when you are not using the hot tub, you can keep it at a lower temperature, or even switch the heating off completely, because it won’t take long to bring it up to the temperature when you are ready to use it.

The main reason is the length of time required to heat a hot tub with an electric heater – typically up to 24 hours, using cold water. To speed things up, some owners ‘pre-fill’ their tub with hot water from a boiler, but even this can require a further 6 to 10 hours of heating to achieve the required 38-40 °C temperature.

Whilst many domestic users were prepared to put up with the inconvenience, commercial users such as holiday parks, could not!

The demand for hot tubs when booking holiday accommodation has risen dramatically and is now the second most requested guest facility. To meet this demand, holiday venues had to find a faster way of heating them, due to guest changeover periods. Typically, there is only around 4-5 hours available to drain, clean, re-fill and heat up a hot tub before new guests arrive.

The solution was relatively simple – use an external heat source such as a gas boiler and simply bypass the hot tub’s electric heater. To enable this, a heat exchanger is required to transfer heat from the boiler water to the hot tub water. It’s exactly the same principle used for most swimming pools, but just on a smaller scale.

Bowman developed an ultra-compact heat exchanger that could be installed in the hot tub’s pipework and the result was hot tubs heated in 3-4 hours using cold water, or in around 1 hour using pre-heated water.

There was also another benefit. Heating hot tubs with electricity can be very expensive. By switching to gas boiler heating, many users reported a significant reduction in the energy costs – some as much as £500.00 per hot tub!

How holiday parks can benefit by switching to gas heating.

More information on Bowman’s hot tub heat exchangers.




In a shell and tube heat exchanger, coolant usually flows through the central ‘tube core’ to cool hot oil, water or air, which passes over and around the tubes. The direction in which the two fluids travel through the heat exchanger can be either ‘parallel flow’ or ‘counterflow’.

Parallel flow is where the fluid to be cooled, flows through the heat exchanger in the same direction as the cooling medium. Whilst this arrangement will provide cooling, it has limitations and can also create thermal stress within the heat exchanger, as one half of the unit will be appreciably warmer than the other.

In counterflow cooling, the incoming cooling medium absorbs more heat as the ‘hot’ fluid travels in the opposite direction. The cooling medium heats up as it travels through the heat exchanger, but as colder water enters the heat exchanger it absorbs more heat, reducing the temperature much lower than could be achieved with parallel flow.

The mean temperature difference between the cooling medium and the fluid being cooled is also more uniform along the length of the heat exchanger, reducing thermal stress.

Depending on flow rate and temperature, the heat transfer performance could be up to 15% more efficient with counterflow, possibly enabling a smaller heat exchanger to be used, saving space and money!

More information on the benefits of counterflow.


During the course of its operating life, a shell and tube heat exchanger will need cleaning many times. Both fresh water and sea water cooling media today contain high levels of minerals and pollutants, which can build up over time, restricting the water flow through the tube core, resulting in a reduced flow rate and significantly lower heat transfer efficiency.

The good news is that Bowman shell and tube heat exchangers are much easier to clean than many other types and the following information is intended as a basic guide:

  1. Removing the end covers gives access to the tube core, which can be removed from the body (or shell).
  2. The tube plates and external tubes can then be washed using a handheld hose or lance. A steam cleaner can also be used, if available.
  3. Small diameter rods or tube brushes can be used to clean through each tube to remove any stubborn deposits.
  4. Detergents or chemicals can be used, if tube fouling is severe. Allow plenty of time for the cleaning media to work before hosing down with plenty of water. NOTE: it is important to check any cleaners being used are compatible with the tube material.
  5. Thoroughly flush the tube core with clean water to remove all traces of cleaning chemicals/detergents and if necessary, neutralise the cleaning fluid.
  6. Reassemble the tube core into the body, refit the end covers in their original orientation and tighten to the recommended torque figures – NOTE: always use new ‘O’ seals after cleaning to ensure a watertight joint.

For more detailed information on care and maintenance of your Bowman heat exchanger or oil cooler, download a copy of our ‘Installation, Operation & Maintenance guide’.

Swimming pool heat exchangers work by transferring heat energy from a hot water circuit, to the cooler pool water circuit, without the two fluids ever coming in direct contact with each other.

Most swimming pools are heated via a boiler, using fuels such as Gas, LPG or Biomass, as the energy source. In theory, the most efficient way to heat the pool water circuit would be to connect it directly to the boiler.

Were this to happen, the chemicals and minerals added to the pool water to keep it safe for use, would quickly erode and damage vital components inside the boiler, leading to premature failure and a costly replacement.

However, by using a heat exchanger to act as an ‘interface’ between the boiler water circuit and the pool water circuit, the boiler is protected from damage and the pool water is quickly heated up to the required temperature for use.

Shell and tube design heat exchangers are extremely popular for swimming pools, due to their efficiency and ease of maintenance. Inside the ‘shell’ there is a bundle of tubes, known as the ‘tube core’, through which the pool water passes in a single direction.

At the same time, hot water from the boiler is circulated around the outside of all the tubes in the tube core. Traveling in the opposite direction to the pool water flow, the boiler water transfers its heat to the pool water, before being recirculated back to the boiler, for reheating.

Both water circuits operate in a continuous heating cycle, until the total pool water volume has reached the required temperature, which is usually around 28 – 30 °C.

Bowman manufactures a comprehensive range of swimming pool heat exchangers for everything from spa pools and hot tubs, up to Olympic size pools.

More information on Bowman swimming pool heat exchangers.


Selecting the correct heat exchanger is very important to ensure the pool heats up quickly to desired temperature. The main issues to consider when sizing a swimming pool heat exchanger are;

  1. Pool size – what is the water capacity? Heat exchangers are sized according to capacity, so a unit designed to heat a 80 m³ (18,000 gal) pool would be no use, if you have an 180 m³ (39,500 gal) pool.
  2. How is it heated? Usually, the choice is either a boiler or renewable energy. If it’s renewable energy, select a heat exchanger specially designed for the lower temperature water provided by solar panels or heat pumps, as these units need less energy to heat the pool to the required temperature.
  3. Boiler water temperature – however, most pools will be heated by boilers, so what is the temperature of the boiler water? Usually, it’s between 80 °C and 85 °C – the ideal temperature for pool heating. Some boilers are lower – around 60 °C. So, using 82 °C water, a heat exchanger providing 110 kW should heat your 180 m³ pool efficiently. But if the boiler water temperature is only 60 °C, the heat available to transfer drops to around 60 kW – a reduction of over 40%, so a larger heat exchanger would be required for the pool to achieve full temperature.
  4. What are the water flow rates? Flow rates are vital for the heat exchanger to transfer thermal energy to the pool. If the hot water flow rate is too low, the available energy will not be passed through the heat exchanger. However, the flow rate of the pool water is equally important. People often think it is important to generate a large temperature differential between the pool water entering and leaving the heat exchanger. They are happy, if the pipework connected to the outlet of the heat exchanger is noticeably warmer than it is at the inlet. In reality, this actually reduces the efficiency of the heat transfer process! This is because the pool water flow is too low – the water remains in the heat exchanger for too long, so a much smaller volume of water is being heated to a slightly higher temperature. However, with higher flow rates, the time taken to turn over the pool water will reduce and even a small increase in the temperature of the pool water through the heat exchanger (1.5 °C for example) will have a greater effect on the heating efficiency of the pool.

More information about heat exchanger selection, read the article ‘Why doesn’t my pool heat up faster?’

Many water cooled internal combustion engines (ICE), can be adequately cooled, simply by pumping the engines coolant through an air cooled radiator.

Cooler ambient air is drawn into and through the radiator by a cooling fan, transferring heat from the engine coolant as it is pumped through the radiator.

But there are applications where air cooling is either less efficient or not an option for an ICE. This could be due to insufficient air flow, or ambient air temperatures being too high, and in these situations, water cooling is a proven solution.  Moreover, replacing the radiator with water cooled heat exchangers can save valuable space and considerably reduce noise.

Installing water cooling is quite straightforward as instead of a radiator, a heat exchanger, usually of ‘shell and tube’ design, is installed into the engines cooling system.

The heat exchanger has two circuits; one will be connected to the engines cooling circuit and the other connected to a source of cool water, which could be seawater for a marine engine or fresh water for applications such as irrigation systems, power generation, fire protection or automotive engine testing.

The cooling water is pumped through a central tube core in the heat exchanger, whilst the engines coolant flows over and around the outside of the tubes, transferring heat from the engines coolant circuit to the cooling water as it flows through the unit.

Whilst there are many heat exchangers suitable for cooling engines, Bowman’s Header Tank units are particularly successful due to the design, which incorporates and integral expansion chamber above the tube core. This eliminates the problem of air pockets or air locks getting into the cooling stream. There is also has a special de-aeration feature, plus pressurised filler cap, making integration very much easier. For more information on Bowman Header Tank Heat Exchangers

As their name suggests, hot tubs require a lot of heat to achieve and maintain the 38°C to 40°C water temperature they usually run at.

Most hot tubs are supplied as standard with an electric heater already installed. This usually takes many hours to heat a typical 1,400 litre hot tub from ambient water temperature to normal operating temperature, and as electricity is one of the most expensive ways of heating, it’s not surprising that many users find their electricity costs rise sharply!

A more efficient solution is to heat the hot tub from an external heat source, such as a gas boiler. Usually, this can be done by connecting pipework from the hot tub to the boiler, in a similar way to adding a new radiator to a new room in a home.

The only difference is the hot tub requires a heat exchanger to act as an interface to keep the pool and the boiler water separate from each other. Installing the heat exchanger into the pool water circuit and connecting to the boiler is straightforward, though a plumber may be required to install.

Once the hot tub is being heated from the house boiler, many users notice how much quicker the water temperature increases and in many cases, the hot tub can be ready to use in just 2 -3 hours of heating, which is a real bonus, as it significantly reduces the energy used and, as gas heating costs are much lower than electricity, energy costs are significantly reduced too!

Bowman has been one of the pioneers in providing hot tub heating via heat exchangers and have a comprehensive range of products for this specific application. For more information on Bowman Hot Tub Heat Exchangers

Although electric propulsion for marine vessels is still relatively new, it is experiencing significant growth and development as the industry seeks to reduce marine CO² emissions.

Currently, many system manufacturers are choosing shell and tube heat exchangers for their electric propulsion systems for the following reasons:

Coolant Flow

In many electric and hybrid marine applications, the coolant flow around the electrical components is usually much lower than the seawater cooling flow. Shell and tube heat exchangers are much better at handling the imbalance of coolant velocities than other types of heat exchanger, such as plate types.

Easier integration

The compact design of Bowman shell and tube heat exchangers, combined with the lighter weight of their titanium units, makes them easy to integrate into the system design.


With rising pollution levels, Bowman shell and tube heat exchangers are less affected by blockages from sea borne debris, compared to plate types.

Bowman manufacture a comprehensive marine heat exchanger range for electric and hybrid applications and are already specified by some of the leading manufacturers and system integrators.  For more information on Bowman Electric & Hybrid Marine heat exchangers

Intercoolers (also known as Charge Air Coolers) improve the combustion efficiency of engines fitted with forced induction (either a turbocharger or supercharger) increasing the engines power, performance and fuel efficiency.

Turbochargers compress incoming combustion air, which increases its internal energy, but also raises its temperature. Hot air is less dense than cool air, thus its combustion efficiency is reduced.

However, by installing an intercooler between the turbocharger and the engine, the incoming compressed air is cooled as it passes through the intercooler, restoring its density to give optimum combustion performance.

An intercooler acts as a heat exchanger, removing the heat generated during the turbochargers compression process. It does this by transferring the heat to an other cooling medium, which is usually either air or water.

Air cooled intercoolers

These are similar in principle to a car radiator in that cool air is drawn through the fins of the intercooler, transferring heat from the compressed turbo air to the cooler air.

Water cooled intercoolers

Where air cooling isn’t an option, water cooled Intercoolers offer a highly efficient solution. Usually based on a ‘shell and tube’ design, cold water flows through the central tube ‘core’, whilst the hot charge air flows around the tubes, transferring its heat as it travels through the heat exchangers.

Bowman manufacturer a wide range of water cooler Intercoolers (Charge Air Coolers), suitable for both marine and land based stationary engine. For more information on Bowman Charge Air Coolers

A CHP (Combined Heat and Power) unit generates electrical power and heat from a single energy source.

There are three primary components within a CHP unit, starting with the Prime Mover, (usually a reciprocating engine) that creates the motive power to drive the Electrical Generator. The final component is the Heat Recovery system, which comprises of single or multiple heat exchangers installed on key areas of the engine, to recover waste heat produced as a bye-product.

In an engine powered CHP unit, around 30% of the fuel used gets converted to electrical power. At the same time, around 50% of the fuel energy gets converted to heat. Without heat recovery, this valuable and highly usable energy stream would be lost to the atmosphere, wasting around half the cost of all fuel used to power the generator. By recovering this heat energy, the generating sets overall efficiency is improved to around 80% – even more in some installations – making CHP a highly efficient energy solution.

Recovered heat can be used for a wide range of domestic, commercial or industrial uses, including space heating and hot water, process heating, as well as cooling, or even generating more power!

Heat can be recovered from the engines exhaust stream, plus its cooling, lubrication and induction systems, using heat exchangers.

Bowman manufacture a comprehensive range of CHP heat recovery heat exchangers for exhaust gas, engine and induction cooling. For more information on Bowman CHP heat exchangers

Combined Heat and Power (CHP) is an extremely efficient method of generating electrical power and heat energy, from a single source.

Most ‘off-grid’ electricity is produced using an engine driven gen-set, usually powered by diesel or gas fuel.

However a typical gen-set, producing electricity only, is often only around 30% efficient.

That’s because only around 31% of the fuel used is converted to electrical power. The remaining 69% is lost throughout the operating cycle.

The largest element of energy loss is heat –  around 49% in total, so by recovering it, a valuable ‘free’ energy source is obtained, which also boosts the gen-sets overall efficiency to around 80%!

Heat exchangers are the most effective solution for recovering waste heat energy, as they convert it to hot water, which can be used for space heating, and hot water in residential or commercial buildings, industrial process heating, generating more power or even cooling via a chiller.

Heat can be recovered from virtually every area of the engine, including the exhaust stream, the cooling and lubrication systems, plus the induction air system.

Bowman manufacture a comprehensive range of CHP heat exchangers enabling customers to convert their gen-set into a highly efficient CHP system.

There are a number of factors to consider when projecting the life of a marine oil cooler.

For example, has the correct product been selected for the cooling requirement?

Has it been installed and commissioned correctly?

Is the velocity (or flow rate) and pressure of the cooling medium within manufacturers recommendations?

Has the unit been maintained and serviced in line with manufacturers requirements?

Assuming all the of the above questions (and possibly a few more) have been correctly addressed, there is no reason why a good quality marine oil cooler, from a well known, reputable company such as Bowman, shouldn’t last for more than 20 years.

But to achieve this, it’s vital that the unit is correctly specified, installed, commissioned and maintained.

For example, on marine oil coolers fitted with Cupro-nickel tube stacks, it is vitally important to ensure the copper-nickel alloy tubes are ‘conditioned’ correctly, to enable the thin layer of natural protective film to form on the tube surface, to provide long term corrosion protection.

Additionally, if the manufacturers recommended water flow rate is exceeded, high velocity seawater entering the oil cooler can quickly erode the tubes and tube plates, leading to premature failure, so following the guidelines is critical!

And the well documented rise of plastic waste in our oceans, means that in addition to having adequate filtration of the incoming seawater, it’s also really important to inspect and clean an oil cooler regularly, to maintain its performance and extend the life of the unit!

The good news is that if looked after correctly, a marine oil cooler can operate reliably for decades.

In fact Bowman often hear of instances where their marine oil coolers have been working for more than 40 years!

Bowman manufacture a very wide range of oil coolers to suit most marine applications and have a computer based selection programme, to recommend the correct unit for the application.