(800) 952-0121          email icon1 

How Does Direct Steam Injection Work?

Ideal for heating liquids and slurries over a wide range of viscosities and solid contents to precise temperatures.

   Example of Direct Steam Injection - Hydroheater - Direct Heat Exchange - Internal Modulation JetCooker





How Direct Steam Injection Works

Direct steam injection works by directly injecting steam into a process fluid to obtain more rapid heat transferring, resulting in more efficient energy usage than indirect heat exchangers. This efficient process of heating is caused by our direct steam injection Hydroheaters’ ability to control both steam flow and mixing turbulence by using a modulating stem plug and nozzle assembly in the heater. This precise mixing of a measured amount of high velocity steam directly with your liquid or slurry provides an instantaneous transfer of heat from steam to the liquid. This method of heat transfer allows for 100% thermal efficiency and energy savings of 20-25%. Don’t believe us? Head over to our Energy Savings Calculator to get an accurate estimate of how much you can be saving in operating costs.


Hydroheaters/Jetcookers control both steam flow and mixing turbulence by employing a modulating stem plug and nozzle assembly inside the heater. The precise mixing of metered amounts of high-velocity steam directly with a liquid or slurry provides instantaneous transfer of heat from steam to the liquid.

To accomplish this, a precisely engineered, variable-area steam nozzle meters the flow at the point of injection and contact with the fluid. The large pressure drop from full steam pressure to the process fluid pressure ensures high-velocity choked steam flow and instantaneous mixing of the two streams. When steam flow is choked, its velocity at the nozzle exit is constant regardless of the total mass flow injected. The internally modulated Hydro Thermal heaters control the amount of injection area (cross-sectional area of the nozzle opening) to precisely regulate the heat load. The constant steam velocity results in consistent and stable operation across the full range of operation.

Hydro-Thermal’s patented direct steam injection heaters use direct heat exchange as a means to transfer 100% of the steam’s energy for heating liquids and slurries over a wide range of viscosities and solid contents to precise temperatures. A Hydroheater’s internal modulation assures exacting steam control, rapid temperature management, and produces predictable results. Each Hydro-Thermal heater has internal trim custom designed to each customer’s specific needs and requirements. 

Hydroheaters/Jetcookers commonly outperform other forms of direct steam injection as well as indirect heating methods such as heat exchangers. Below is an overview of indirect vs. direct heat exchange and how Hydro-Thermal’s patented technology outperforms the status quo.

Get a Quote

external vs. internal modulation - direct steam injection

External vs Internal Modulation:

Externally or Internally modulated direct steam injection refers to how the mass flow of steam injected into the process fluid is controlled.

External modulation uses a steam control valve on the supply line to vary the pressure of the steam at the point of injection: Varying the pressure changes the steam density and velocity through the nozzle to control the amount of heating. Regulating steam pressure to control heating can result in unstable operation, hammering and vibration, when high or low steam flowrates are are required. At low steam flow, ie. trim heating, the differential between steam pressure and process can be very small and a slight fluctuation in either pressure can cause an upset. Alternatively, at high steam flow requirements, ie. max heating at startup, the orifice or nozzle size will allow more steam than can be condensed and steam hammer occurs.

Internally modulated DSI controls the injection area rather than steam velocity and density to regulate the amount of heating. An internally modulated heater operates at higher steam velocities compared to external modulation. This higher velocity produces improved, often rapid mixing and nearly instantaneous condensation of the steam into the process fluid.


Direct vs Indirect Heating:

There are two basic types of heat exchangers used to transfer heat between process fluids — direct heat exchange and indirect. Indirect heating is most commonly seen in the form of plate & frame or shell & tube heat exchangers. Any process that does not allow direct mixing of steam and fluid is indirect heating. Heat exchangers transfer heat through a membrane or solid wall. This results in only ~ 83% of the heat energy transferred to the process fluid while the remaining energy is discharged in the condensate formed from the steam.

Direct heating, on the other hand, uses 100% of the steam’s heat energy by adding steam directly to the process fluid. The benefits of using direct contact heating vs. indirect include:

    • Energy savings of 25% or more
    • Precise and instantaneous temperature control is possible to within 1°F
    • Reduced footprint for direct steam injection system
    • Reduces maintenance via self-cleaning and elimination of a condensate return system

Additional benefits:

    • Rapid and uniform heating -important in starches and food product
    • Can heat highly viscous fluid
    • Handles fluids that are difficult  to heat—avoids “bake-on”; abrasive slurries
    • Eliminates plugging and fouling of the heat transfer surface
    • Rapid response time

What is direct steam injection? Spectrum of direct steam injection technologies

Direct Steam Injection Spectrum

Hydro-Thermal’s heaters utilize direct steam injection. This general term refers to any type of fluid heating that utilizes steam being directly mixed with water or process fluid. There are many forms of direct steam injection including: spargers, eductor pumps, externally modulated heaters, and internally modulated heaters. Each method varies in its levels of complexity, with sparging being the most simple and internally modulated having the greatest level of technology and control.



Sparging is the oldest, simplest and least complicated technique for mixing steam with liquid or slurry to affect heating. It is basically injecting steam directly into a fluid filled tank. Though considered simple and inexpensive, sparging is very inefficient and the operation invariably results in:

  • Poor heat injection economics due to steam energy escaping from vessels without condensing.
  • High maintenance costs for tanks, sensors and piping are the norm if the equipment operates outside the design parameters.
  • Equipment failure (both vessel and sparger pipes) due to the vibration associated with steam hammer when not operated within their narrow design envelope.
  • Usually less than satisfactory on/off process control. A sparger is the least controllable direct steam injection heating method.
  • Non-uniform heating

If you want more information, head over to our Direct Steam Injection VS Steam Sparging page!


Mixing Ts

Mixing Ts combine separate streams of steam and cold water to produce heated water. Because accurate temperature control is difficult to maintain with this method, mixing Ts are not the best choice for process fluids. When used for water, mixing tees are prone to scaling, fouling and excessive hammer. Their operation often requires the steam and water pressure to be very close to each other for balanced mixing. When either steam or water pressure fluctuates slightly, the higher pressure line can overcome the other and backfill the piping. This can result in live steam discharging the system. The drawback of Mixing Ts are:

  • Very high maintenance
  • Prone to scaling and fouling
  • Steam hammer is common
  • Potentially very dangerous due to live steam being close to human contact
  • Limited temperature control


Sparge Tube

The externally modulating sparger tube (MST) heater consists of a spring controlled, variable-injection sparger tube inside a cast process flow body. In response to a temperature sensor, the external flow control valve modulates the steam to a spring-loaded piston. MST heaters work reasonably well on clear liquids and some low solids solutions but are subject to severe clogging and steam hammer if frequent maintenance is not performed. In typical water heating applications, these devices typically require monthly tear down and acid bath cleaning. Since the steam flow is dependent upon a spring loaded valve, accurate temperature control is difficult once the spring begins to wear. Additionally, if low (trim heating) or high steam flow is required, the spring mechanism can have difficulty with accurate or stable control. Spring failure is a common issue with this type of heater. Additional drawbacks of sparge tubes are:

  • Requires external steam control valve
  • Very high maintenance
  • Prone to scaling and fouling
  • Steam hammer common
  • Limited temperature control due to external control
  • Internal spring prone to wear and breakage


Internal Modulation

Hydro-Thermal’s technology, which utilizes internal modulation, is the most advanced form of direct steam injection. It has many benefits over other direct heating methods including:

  • Reduced steam consumption
  • Significantly lower energy costs, 100% efficient use of steam energy
  • Low maintenance
  • Handles fluids that are difficult to heat—avoids “burn-on”; highly viscous or abrasive slurries are no problem
  • Small footprint
  • Consistent, precise discharge temperature
  • No condensate return required


If you want more details, head over to our Benefits of Direct Steam Injection page.

Fill out one of our Quote Forms to get started and find out how we can help you today!

Are you wondering what applications are ideal for direct steam injection? You can see all the Industries we work with here.

Learn more about Hydro-Thermal’s products here, or for more information on direct and indirect heating, click on the technology downloads button below.


Technology downloads about direct steam injection




  • Products
  • Applications
  • Technology
  • RFQ/Service
  • Maintenance

How do I know if a Hydroheater is the right choice for my application?
Buying a new piece of equipment is a major decision. We will guide you through the purchasing process, so you can be confident in your investment.

To help us understand your needs, first we will have you fill out a quote form. Our customer service staff  will contact you with additional questions in order to assess your needs and expectations. This will also help us work with you to ensure that our technology is a good fit with your application.

Once we collect your process conditions and review your specifications we will develop the optimal technical and economical solution for your requirements. Additional consultation may occur to ensure that the best solution is identified.

To start the process, complete a quote form or call (800) 952-0121 or (262) 548-8900 and ask for Customer Service.

What materials are used in Hydroheaters?
The standard material for Hydroheaters is grade 316 stainless steel. Other metallurgies are available based on requirements for corrosiveness, abrasiveness, or other conditions that may require a variance from our standard materials. we can use 317L, Hastelloy, 254 SMO, up to AL6XN

Are Hydro-Thermal products ASME certified?

They are designed per ASME code, but are not certified. They can be certified upon special request.

Can your products be used to heat abrasive fluids?

The Hydroheater is very robust and reliable, and can be further enhanced as needed for heating abrasive fluids. For many applications, a weld overlay and enriched material in key areas is sufficient. Some applications such as slurries with sand content require additional overlays outside the basic weld overlay. This technique has greatly increased the heater’s internal component lifespan. Other fluids have required more extensive modifications. In oil sands froth heating applications, for example, a combination of a weld overlay as well as the use of hard, abrasive resistant materials is recommended. For specific requirements for your application, please contact Hydro-Thermal directly.

What types of media can a Hydroheater heat?
A Hydro-Thermal Hydroheater can heat a diverse array of fluids, from water to heavy, viscous slurries. Based on the type of heater you choose we can heat tomato paste, medium consistency pulp stock or higher solids content.

We also offer options that utilize low shear flow. This makes it ideal for food slurries with high solid contents where viscosity, chunk size, and overall integrity of the product must be maintained.

If the media you want to heat can accept steam, this is your solution.

What is Direct Steam Technology (DSI)?

Ideal for heating liquids and slurries over a wide range of viscosities and solid contents to precise temperatures. Click here for more information.

How long have Hydroheaters been around?
The technology behind direct steam injection was developed in 1911. Inventors John White and Roy Miller patented heating equipment using steam to precisely control water temperature in 1927. Manufacturing industrialist, Harry Schauer invented the Hydroheater in 1934 for use in a paper mill in Wisconsin.

Today, more than 80 years after the Hydroheater was invented, Hydro-Thermal has taken the technology and expanded its application across diverse industries.

How do I request a quote?
Unlike heat exchangers, kettles or spargers, the Hydroheater is engineered specifically for your process conditions and unique application. We need to know a few things about your conditions, such as temperature range, steam pressure, and flow rates to size a heater specifically for you.

Completing this form is the first step in getting a quote. For assistance, click here or call (800)952-0121 or (262)548-8900 and ask for Inside Sales.

How do I identify the model number and/or serial number of my heater? 
To locate these numbers, first look at the heater itself. There you will find a Hydro-Thermal name plate with the model number and serial number engraved on it. Do not take the numbers off the actuator as those are not the Hydro-Thermal identifiers.

How do I request a field service technician to help maintain my heater or heating system? 
For standard field service, please use this form and a member of our team will be in touch.

Please call us at 800.952.0121 for urgent matters. If the issue is outside of normal business hours, please listen to the prompt on the after hours message for “Emergency Service.”


How often do I need to perform preventative maintenance on my heater?

Proper care of your Hydroheater will save time, money, and prevent unscheduled shutdowns. Whether you want to maintain your heater yourself or have Hydro-Thermal service it for you, we have options to keep your system running at optimal performance. Click here for maintenance options.

How do I obtain the operator’s manual for my heater? 
Simply go to the Knowledge Center, find your heater model, click the corresponding link, and the manual will be downloaded to your computer. To access to the Knowledge Center, click here to create an account or log in.

HTC.logo.white1 01

Hydro-Thermal is the global leader in the development and manufacturing of Hydroheaters. Through our vast global channel partners, we support hydro heating in six continents and all industrialized areas. We create heating systems for a variety of industries including: pulp, paper, chemical, ethanol, food & beverage, metal, & more!

Hydro-Thermal Corporate 

400 Pilot Court
Waukesha, WI 53188 USA
Phone: (262) 548-8900
Fax: (262) 548- 8908