Direct Steam Injection Heaters

Direct steam injection heaters are used for heating water and water-based fluids. Steam bubbles are injected directly into the target fluid with a nozzle or diffuser. The steam bubbles transfer heat energy to the fluid.

Just as direct heaters are the most efficient heating method, direct steam injection (DSI) is immensely efficient. Because the steam bubbles are injected right into the fluid, its thermal efficiency is 100%.

This results in energy savings of 70% to 80%, which can significantly impact operating costs. That alone is reason enough to consider direct steam injection. Other methods can lose that 20% to 30% efficiency as energy transfers into condensation.

How They Work

The basics of direct steam injection are relatively simple. The target fluid is in a pipe or vessel which the DSI nozzle is inserted into. Steam bubbles are injected directly into the fluid, and the heated fluid is then transferred wherever it will be used.

The differences in how direct steam injectors work depend on the type of DSI heater used.


Sparging is an older method of injection. It has low costs and a simple design that is easy to install. The downside is that sparging is less efficient with greater maintenance costs and equipment failure risks.

The steam supply enters a pipe in the bottom of the vessel, where the heat radiates upwards through the fluid.

Though simple, this method offers little control and less uniform heating than other options.

A sparge tube advances the sparging method. The steam supply feeds directly into a spring-loaded steam piston which sits at the inlet of the cold water supply, producing hot water at the outlet. Although it is more reliable, sparge tubes are at risk of spring failure and scaling.

Mixing T

A mixing T gets its name from its shape. The horizontal line of the T has steam introduced from one side and cold water from the other. The two mix together in the middle to create heated water, which comes out the bottom of the vertical line of the T.

A lot of maintenance is necessary to prevent fouling and the discharge of steam since the water and steam pressures must be similar to prevent issues.

Internal Modulation

Internal modulation is the most precise method of direct steam injection. It requires less steam and does not require condensate return.


Direct steam injection heaters can be used for any application using medium or high-pressure steam that requires hot water for water or water-based mediums. A few common applications include:

  • Boiler Feedwater – preheating for more efficient steam generation
  • Cleaning Stations – machine and parts cleaning
  • Washing – rapid heating
  • Wastewater – heating wastewater sludge

Direct Heaters

Wattco custom manufactures electric inline heaters and heaters for direct steam injection. Our team of experts works with you to determine the best heater type, configuration, and materials for each project and budget. Contact Wattco today for electric heater quotes and information.