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Circulation Heaters

Indeeco circulation heaters are used to maintain, raise, preheat and boost process temperatures from -50° F to 1200° F for a wide variety of liquids and gases found in commercial, industrial and military applications.

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The Series 352 (12 W/In2), 354 (20 W/In2) and 356 (50 W/In2) INDEECO circulation heaters are designed for heating gases, water and oil.

Stainless Steel

The series 350 (12 W/In2), 357 (20 W/In2) and 358 (50 W/In2) Indeeco circulation heaters are designed for heating mildly corrosive liquids or pure water solutions. This design may also be used for heating gases or liquids to high temperatures with optional thermostat and high temperature construction described in the Special Features section.


The Series 351 (12 W/In2) and 353 (20 W/In2) Indeeco circulation heaters are designed for heating oil.


The Series 355 (50 W/In2) Indeeco circulation heaters are designed for heating water.


These compact, light-weight, easy to install heaters can be used for many commercial or light industrial water heating applications.

Standard Construction

The standard circulation heater construction includes an Indeeco Pipe Thread or Pipe Flange Immersion Heater mounted in a thermally insulated pressure vessel with inlet and outlet nozzles. A factory installed and pre-wired thermostat provides automatic process temperature control. Six heater mounting options are available to meet your specific installation requirements.

Immersion Heater

Designed and built by Indeeco, all pipe thread and pipe flange immersion heaters include these standard features.

Industrial Grade tubular elements are manufactured by Indeeco. The .475" diameter design provides extra electrical insulation for better dielectric strength.

Element Spacers, made from material similar to the element sheath, maintain a uniform distance between elements. This prevents hot spots that can reduce heater life and burn temperature sensitive materials flowing through the circulation heater. Spacers are perforated to allow for maximum flow and are installed in a manner to allow the heating element to expand and contract freely. Element bends are repressed 360° at the U-bend area to improve dielectric insulation integrity and to prevent potential hot spots.

Moisture-Resistant Epoxy Terminal Seals are standard for all circulation heater designs with maximum process temperatures of 250° F.

Permanent Bus Bars are provided to prevent field failures due to loose electrical connection. Pressure connectors are attached to the bus bars for field wiring of heavy gauge wire. Stainless steel bus bars are standard. 


An Indeeco Type DA thermostat is factory-mounted and prewired to give automatic process temperature control. The standard range is 60-250° F. Its liquid-filled sensing bulb has an inherent sensitivity of ± 5° F; however, the actual process temperature differential depends on a number of application factors.

The Type DA thermostat comes complete with integral on/off switch, pilot light and external adjusting knob. Heaters provided with pilot duty thermostats require field wiring to a magnetic contactor (see Table IV in "Mechanical and Electrical Guidelines").

System Configurations

Closed Loop Systems

The circulation heater is installed in a system where the
liquid or gas to be heated is recirculated through the heater in a closed loop configuration.

Applications of this method fall into the two distinct categories of Indirect and Direct Heating.

Indirect Heating

A heating medium such as Dowtherm, Therminol, ethylene glycol, water, oil or steam is heated as it flows through the heater. The heating medium is continuously recirculated through coiled tubing, pipes or vessel jackets which are wrapped around or inserted directly into storage tanks, vessels, molds, dies, presses and rolls which are to be heated.

Typical Applications Include:

  • Viscous fluids and other temperature sensitive materials such as adhesives, asphalt, chocolate, syrups and varnish found in tanks and process vessels.

  • Corrosive materials like acids and chemicals which would quickly corrode heating elements directly immersed in the material.

  • Platens, molds, presses or rolls found in plastic injection molding/extrusion processes, textile industries and food processing plants. Some systems may involve high temperatures and pressures.
Direct Heating

The process liquid or gas is recirculated directly through the heater in a closed loop system. Selecting the proper element watt density is very important. If the watt density is too high, the process fluid may carbonize or break down chemically.

Typical Applications Include:

  • Testing systems such as a test stand where the circulation heater is used to maintain uniform oil temperature during the testing of automobile engines. Laboratories and R & D centers have similar applications for a wide variety of liquids and gases.

  • Drying systems where recirculated air or steam is heated or boosted to dry inks, textiles, bottles, pharmaceutical powders, cure parts or remove moisture from pressurized air systems.

  • Winter freeze protection for water tanks, cooling towers and sprinkler systems.

  • Diesel generator sets where cooling water and lubrication oil must be kept warm to assure fast start-up in cold weather.

  • Lubrication and hydraulic oil heating for maintaining the correct oil temperature and viscosity which is crucial for efficient operation of the pumps, transmission, engine or other equipment in the closed loop system.

  • Industrial processing tanks or baths which use the circulation heater to provide precise temperature control for oil quenching, cleaning tanks, rinsing tanks, degreasing tanks and water baths.

Advantages of circulation heater systems compared to direct immersion heaters for tank heating applications include:

  • Heating elements are located away from areas of heavy sludge build-up or possible physical damage.

  • Tank interior is kept open for process operations.

  • Tank is easier to clean.

  • Heater can be removed for inspection without draining the storage tank.

Open Heating Systems

The circulation heater is used in a system where the liquid or gas flows through the heater only once and is discharged directly into the application.

Typical Applications Include:

  • Booster heating systems which increase the temperature of the liquid, gas or steam just prior to being discharged directly into applications, such as steam cleaning, commercial dishwashers and high temperature process gas heating.

  • Fuel oil heating where the circulation heater raises the temperature of fuel oil to reduce its viscosity, facilitating its flow into the burner.

  • Spraying systems which use the heater to reduce viscosity or preheat the material before being pumped into a spray nozzle. For example, heavy petroleum is heated before it is sprayed over the top of coal to reduce dust and coal from being blown out of open railroad cars.


For product specifications, refer to our technical document center.

Download the refinery heater evaluation checklist


Heater not passing maintenance turnarounds? Use these steps — the same procedures heating suppliers use — to evaluate your equipment. Download the five-step checklist.