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Thermal fluid or steam?: Key considerations

16 July 2015

Thermal fluid heaters can be used as a source of heat for industrial processes where high process temperatures are required and, according to Doug Howarth, sales and marketing manager of Fulton, there are circumstances, especially where low running costs is a requirement, where they are more suitable for heat transfer than steam systems

Water and steam are typically used as heat carriers in heating systems, but at high temperatures, both require a corresponding high operating pressure. For industrial heating systems, a high temperature is often a great advantage, but establishing this with water and steam can be controversial and expensive.

Thermal fluid heaters use specialist oils as heat carriers and operate at atmospheric pressures to 300°C. To gain a similar operating temperature from traditional water- or steam-based systems would require a pressure of 85 bar.

A properly designed, installed and maintained thermal system that uses the correct thermal fluid for the application’s operating conditions should give 20 to 30 years of reliable service. However, as with water and steam systems, maintenance is essential for safe and effective operation; and the thermal fluid should be checked regularly to verify that it has retained its heat transfer properties.

Thermal fluid or steam?

The choice between adopting steam or thermal systems is determined by the requirements of the process and its temperature range. In general, if the process requires a temperature below 180°C, steam is usually the first choice. However, if the required process temperature is above 180°C, thermal fluid is often the better solution. 

Thermal systems, unlike steam, provide useable temperature with very little pressure and a variety of cost savings should be expected. The additional control provided by thermal systems also allows multiple, easy and accurate temperatures throughout a single system that can also include cooling. There are also no freezing hazards, they provide rapid start up and shutdown with minimal heat losses and there’s no requirement for blow down or condensate losses. 

The whole life costs for thermal systems can also be cheaper because they require fewer insurance inspections, which minimises production downtime and shut down periods. There’s also no requirement for water treatment or chemical dosing, which leads to zero waste disposal and minimal maintenance costs. 


Fulton offers a range of thermal fluid heaters and multi-fuel-fired steam boilers, so can offer customers an unbiased review of their heat transfer requirements.


Its thermal fluid heaters feature a four-pass, high-efficiency design that pre-heats the combustion air. Their compact construction can, like many Fulton systems, be skid-mounted with ancillary equipment and their layout designed to suit the customer’s requirements. The range includes models with heat outputs to 3500kW and standard operating temperatures of 345°C (400°C is also available with optional heater enhancements and suitable thermal fluids). Fulton’s FT-N features a compact, vertical design with the capacity to operate at temperatures to 340°C and with heat outputs from 22 to 504kW. The FT-C offers outputs from 235kW to 4.1mW and its largest heater, the horizontal FT-HC, provides heat outputs from 0.7 to 5.9mW. 

Technology in action

Specialising in the manufacture of precast masonry blocks, Interfuse’s plants are amongst the most advanced facilities of their kind in the UK and are capable of producing around 21 million dense and lightweight blocks per year. 

The manufacturing process for the concrete and lightweight building blocks uses a press to precast the products and a series of kilns to provide heat for rapid curing and, at its Gainsborough site, Interfuse replaced a live steam system that was proving too expensive to operate, with a Fulton FT-C vertical coil thermal fluid heater. 

Commenting on the installation, Interfuse works manager Len Parks says: "Using live steam for the curing process at Gainsborough was costing the company in the region of £20,000 per month in fuel costs alone, so while the change to the Fulton FT-C thermal fluid boiler proved to be a significant investment, the thermal fluid system’s operating costs are about a tenth of those for the steam system, so we are expecting to achieve payback in three to four years.”

Whilst the decision to change to thermal fluid was based on the company’s positive experience over a number of years with a German-manufacturer boiler at its Syston facility, Interfuse decided that UK-based service and support was essential for the new boiler.

Parks confirms that thermal fluid is much cleaner than the original steam installation and the maintenance costs are significantly lower because no annual strip-down is required. In addition, there are no associated costs for mains water, water softeners or chemicals to run the system, nor are there pressure regulations to adhere to.