Wattco’s In Depth Guide to Circulation Heaters

Circulation heaters, sometimes called In-Line Heaters, are compact heating units used in a variety of ways across industry. Common applications for circulation heaters include heating liquids and gases. These heaters are especially popular in the oil and gas industry, where they are used to control the viscosity of oil and crude.  

Introduction to Choosing a Circulation Heater

Choosing the circulation heater which is right for your application is a careful process which requires the procurement officer to exercise critical judgement and knowledge of engineering if the ideal solution is to be found and implemented. The purpose of this article is to provide a concise, and more importantly, digestible guide which will assist you in finding the ideal circulation heater for your applications.

However, choosing the right heater for your application is only the first step. Next, you must determine the precise heat requirements for your process to inform your choice of construction materials for the various components of the heater. Choosing a material for the flanges, vessel, and heating element sheath is critical for ensuring your heater consistently performs to it’s highest potential for as long as possible. The Watt density of the heater also depends on the temperature requirements, and we will cover all of these topics in this article to help you determine which heater will meet your needs.

Should you have any questions after reading this article or in general, we encourage you to contact us for additional information and requests.

Strong knowledge of your industrial process or application is required to pick the right heater, as is the knowledge of your plant’s designer or chief engineer. The following factors should all be considered when deciding which heater you need. These factors are not listed in order of importance.

  • The medium you are heating. You must determine its viscosity, the required viscosity, specific heat, and its density.
  • Potential contaminants which could be found in the medium. These contaminants could damage parts of the heater if they are not accounted for.
  • The design and material of the vessel holding the medium. These factors must be taken into account and considered alongside the pressure and the temperature of the process.
  • Operating temperature. Learn the precise temperature the unit needs to operate at.
  • Heating-element Watt density, sometimes referred to as heat flux is important to know when determining which material to construct the element from.
  • Is the fluid being heated corrosive or non-corrosive?

A few additional points to consider if the fluid is a corrodent are its temperature, the degree of aeration the corrodent is exposed to, and its velocity through the system. Find specific answers to address each of these factors and share it with your Wattco representative along with a detailed description of your application. He or she can confirm that you have selected the appropriate piece of equipment and help you decide how to customize it, if required.  The engineer at your plant will be an invaluable asset for finding precise and pertinent information.

Maintenance and long term care

As with any piece of industrial machinery, there are operational imperatives which must be maintained to ensure you get safe and long-lasting performance from your Wattco heater.

Firstly, the heating vessel must be completely stable and fixed while in use. Any loose mounting can cause the heater to vibrate and wear down prematurely. The heater must be fixed to a surface securely at all times while in use. When working with heavy, viscous, or high-temperature liquids, using a pump to circulate the fluid and create forced flow will improve the effectiveness of the heating system.

When it comes to mounting the circulation heater, orient the unit vertically such that the top of your heater is not above the lowest possible water level in the tank. Finally, for circulation heaters used in gas applications like steam superheating, compressed air heating, or heating nitrogen or ammonia, it is critical to ensure there is sufficient flow to achieve and maintain the highest vessel and sheath temperatures without sacrificing safety.

Difference Between Circulation Heaters and Immersion Heaters

Wattco circulation heaters are designed to improve the performance of immersion heaters. A circulation heater is built from an immersion heater which is installed into a pressure vessel or into the body of the pipe. We will cover the circulation heater’s construction in further detail below, but generally speaking a circulation heater is an immersion heater modified for enhanced performance.

Circulation heaters are sometimes referred to as “Inline Heaters” because of the heater’s shape, the orientation of the element, and the way fluid circulates within the heater.  

Screw Plug Immersion Heaters for Circulation Heaters

Circulation heaters are constructed of a flanged or screw-plug immersion heater coated in a layer of insulation to create an all-in-one unit. We also manufacture custom and stock immersion heaters for similar applications to circulation heaters. Each heater built and designed by Wattco exceeds our high-quality assurance standard and comes backed by over four decades of experience.

Circulation Heater Applications

Wattco’s circulation heaters are versatile heating units suitable for a range of applications, industrial processes, water heating, and freeze protection, lube, and waste-oil applications being most common. Although circulation heaters can be used for different purposes the material they are constructed of must be appropriate for the application for optimal performance.

Below you will find a brief overview of circulation heaters in different applications along with the corresponding materials for the heater’s sheath and element.

Water Circulation Heaters

Circulation heaters can be used to heat clean water, protect against freezing, store water at a required temperature, and solutions which don’t corrode copper. For these requirements Wattco recommends a copper sheath with flanges made of steel.

Oil Circulation Heaters

Heating oils (especially stagnant and heavy-gauge oils). Some mildly corrosive liquids, and high-temperature low-flow gas heating applications all require both a steel sheath and flange.

Steam/Air/Gas Circulation Heaters

A circulation heater for a steam boiler or for hot water, or slightly corrosive solutions (such as those found in rinse tanks and spray washers) require steel flanges and a sheath made of a superalloy called Incoloy.

Water/Detergent/Oil Circulation Heaters

If you require a circulation heater for process water, detergent or solutions with soap, soluble cutting oils, or demineralized/deionized water, you need a circulation heater with stainless steel sheath and flange.

Corrosive Material Circulation Heaters

Mildly corrosive solutions require circulation heaters with stainless steel components. If you don’t see your application in this article, a Wattco representative would be happy to work out a solution to your heating needs. We offer custom circulation heaters for niche requirements and can build to suit virtually any demand.

Circulation Heater Construction

Watto circulation heaters are designed for heating circulating fluids under pressure. As such, these units must be durable and efficient in order to do their job well and provide strong return on investment.

A Circulation heater is a heating unit securely mounted inside a thermally insulated tank. The heater unit is either a flanged or a screw-plug immersion heater and it sits inside a pressure vessel or the body of a pipe. The heating unit has inlet and outlet valves which allow fluid to pass through the tank unit and reach the desired temperature.

Refer to the diagram on the right for a visual representation of a circulation heater’s construction.

Multi-stage Circulation Heaters

Multistage heating is regulated by the control panel. Multistage heating is a preferred heating method because it enables one to control certain banks of elements interchangeably with different circuits to create a fluid power flow, thereby heating the elements and in turn heating the liquid.

Wattco also offers redundant stages as a precautionary measure in case any existing circuits fail or cease functioning. Should a failure occur, an electricians could change the wiring on to the unused circuit to minimize any production downtime.


Below are listed some of the key features which are standard in Wattco circulation heaters.

  • Sizing is standard: 1.25” NPT screw plug size to 14” diameter. – Steel circulation heater vessels are fitted with 150 lb. flanges for durability and dependable performance.
  • The vessel housing the heater is thermally insulated.
  • Wattco can build custom unit sizes right up to 44” nominal pipe size.
  • Request any special size, wattage, or construction material and we will do our best to accommodate your needs.
  • Larger vessels and/or heavier flanges are available upon request.
  • Each circulation heater is supplied with special design terminal boxes and stainless steel for heat protection in hot environments.


As one of potentially many solutions to heating needs, there are a number of advantages to choosing a Wattco circulation heater.

Wattco circulation heaters are easy to install and compact. These heating systems are highly energy efficient, meaning you save money on electricity. They’re also easy to clean, and are highly durable and suitable for operation in adverse conditions.

The heat distribution from a Wattco circulation heater is even and quickly responds to changes made at the control panel. A circulation heater provides greater wattage in a smaller heat bundle than most alternatives while simultaneously producing maximum dielectric strength.

You will save even more energy with a Wattco circulation heater while protecting and preventing thermal isolation, because of the reduced heat loss from the vessel.

Aside from all their thermodynamic benefits, circulation heaters are versatile due to their easy mounting support. They’re also compatible with general purpose terminal enclosures, terminal enclosures which protect from moisture or weather, and adverse conditions where there may be a risk of explosion.

Each heater produced by Wattco is 100% compatible with standard industry piping and safety standards. Most importantly our heaters are safe, like all of our products.

Common Features

Although Wattco can custom-fit a circulation heater with your required terminal enclosures and mechanical controls, the most common are as follows:

Common Terminal Enclosures for Circulation Heaters

  • NEMA 1 general – purpose enclosure.
  • NEMA 4 & NEMA 4X weather-resistant terminal enclosure.
  • NEMA 7 hazardous location enclosure.

Common Mechanical Thermostat Power Ratings for Circulation Heaters

  • Single throw, single pole, 25 amp thermostat rated up to 240 volts.
  • Single throw, double pole, 25 amp thermostat rated up to 240 volts.
  • Single throw, 15 amp triple pole thermostat rated up to 600 volts.

Common Temperature Ranges for Circulation Heaters

  • Between -16℃ and 40℃
  • Between 10℃ and 120℃
  • Between 70℃ and 280℃
  • Between 160℃ and 370℃

Selecting a Wattco Circulation Heater

Keep the following points in mind when selecting your circulation:

  • What is the operating temperature your operation requires?
  • What watt density does your heating element require?
  • Does your heating application involve corrosive or non-corrosive liquids?

The heater’s sheath material depends on the nature of the fluid being circulated. Other factors to consider include the fluid’s temperature, how aerated the solution is, and the velocity the fluid must travel at.

Prepare answers to these questions and have them ready when consulting with a Wattco representative and he or she will help you determine which circulation heater is ideal for your application.

There are a few general principles it helps to keep in mind when selecting your circulation heater. Firstly, heat generated from an electric heater leaves the heater and not the steam or liquid heat exchanger.

Furthermore, regardless of whether the surface area contacting the application is well fixed the temperature of the sheath of the heating element will increase until it achieves a temperature which is similar to the heat transferred to the process.

Finally, the lower the watt density of the heater, the longer the heater’s lifespan will be, particularly when installed in applications with highly viscous or stagnant liquids. Low-density heaters are more expensive than high-density heaters. Warning: Selecting a heater with the wrong watt density is likely to cause damage to the control systems and/or the product, causing the heater to fail.

Circulation Heater Installation

Circulation heaters can be mounted in one of three configurations, depending on the application. Below are the three orientations and the applications these arrangements are suitable for:

Liquid Heating/Low Temperature Gas Heating

(Terminal Housing Pointing Up)

High Temperature Gas Heating

(Terminal Housing Pointing Down)

Horizontal – Gas or Liquid Heating

Ordering A Wattco Circulation Heater

Wattco has been designing, manufacturing, and innovating in the industrial heating industry for over 50 years and serves a range of clients all over the world. Our dedication to our customers is matched only by our dedication to high quality products. Contact Wattco to find an innovative, cost-effective solution to your problem. It all begins with a consultation with a Wattco representative. From there we get to understand your needs and work together to come up with the most efficient solution. Visit our contact page or contact us at 1-800-492-8826 and get started today.