Wattco Duct Heaters In Depth

By Ilan Toledano
Views: 862
Oct 27 2016



Wattco has earned its reputation for providing high-quality duct heaters over years of long-standing service to a range of industries. Common industries we work with include chemical, manufacturing, oil and gas, food, and the defense industry.

One of Wattco’s newest product lines is our duct heaters. This article will familiarize you with duct heaters, their applications, and everything you need to know to make an informed buying decision.  Should you require additional information or guidance in making a decision we encourage you to give us a call. Alternatively, you can request a quote through our website and we guarantee a quote will be returned within 24 hours.  

Introduction to Wattco Duct Heaters          

Wattco has been manufacturing the electrical heating elements used in duct heaters since 1969. Over the years research, design, development, and experimentation with the latest technologies has led us to produce an adaptable heating method which is compatible with the majority of non-pressurized air heating systems.

In addition to our standard line of duct heaters, Wattco is available to commission custom duct heaters for specialized applications or environments, including adverse environments. Standard Wattco duct heaters can be ordered in different sizes and dimensions in order to fit the space available.

In general terms, duct heaters are a comprised of an open coil, tubular, or finned tubular heating element which can be either flanged or inserted directly into the duct. Duct heaters are split up into two general categories: air duct heaters and process heaters. Air duct heaters are most commonly found in industrial air-flowing ventilation systems and/or comfort heating applications, whereas process duct heaters are primarily used in industrial process heating applications. An example of an industrial process application for a duct heater is in a kiln which requires air to be re-circulated or forced to circulate. We strive to meet each customer’s individual needs and will draw on our 50+ years of experience to come up with custom solutions for non-pressurized air-heating systems whenever possible.

Tubular Duct Heaters

Wattco Tubular duct heaters are designed to transfer electricity into heat with the overall goal of heating up a large space as quickly and efficiently as possible. The common components of a tubular heater include a terminal housing, heating elements, and a control panel to regulate temperature. Each of these elements can be observed in the un-flanged tubular duct heater seen in the image to the right.

wattco-duct-heater-with-open-air-coil

The centre of the tubular heating element there is a resistor wire made of an alloy comprised of chrome and nickel. If an immediate power cut off is required, for emergencies or otherwise, Wattco can install magnetic contactors to ensure the power goes off precisely when required. The electrical wiring which supplies power to the duct heating unit is manufactured to standardized values, ensuring the heater will fit existing ventilation infrastructure.

To ensure the desired rate of airflow can be achieved we install an airflow switch by the heating elements. In addition to the manual airflow switch, we also install an automatic switch called the primary thermal switch. This automatic switch is designed to shut the unit off when the maximum temperature limit is reached. The switch resets automatically once the temperature dips below the maximum limit and is ready to shut the unit off once again. The secondary manual switch is referred to as a secondary cut-off switch.

When the duct heater requires servicing or needs maintenance work, a disconnect switch can be used to shut off the unit’s electrical power supply. The unit also includes a relay switch which ensures that the circulation fan is primed for action before the heater is ready to be activated. This relay switch is referred to as a fan interlock relay. Bushings made of steatite ceramic are present to sustain any mechanical stress on the device. Steatite ceramic is the material of choice for its high dielectric strength and resistance to both mechanical and thermal shocks.

Open coil terminals are also made of steatite, unlike tubular duct heater terminals. These terminals serve as insulation and provide a dependable and, more importantly, safe transfer of electrical power between the control panel and the heating elements. The transformer which ships with Wattco duct heaters is pre-set with a primary voltage rating ranging from 120-600 volts. A protective covering or stainless steel terminal block protects the aluminum and copper wiring. For added safety Wattco installs a ground wire to prevent static build up.

Duct Heater Electrical Capacity

Wattco offers several custom duct heater options with kW capacities up to 1,000 kW. The following voltages can be accommodated:

  • 347 Volts/1 Phase
  • 600 Volts/1 Phase
  • 600 Volts/3 Phases
  • 208/240 Volts/ 1 Phase
  • 208 Volts/3 Phases

To ensure our duct heaters integrate with your process we follow the international Canadian Standards Association (CSA) label which establishes standards for the industry and is recognized by the United States. As described above, our heaters can be fitted with components which can serve to prolong the heater’s operational lifespan.

Determining the Kilowattage Required for Your Duct Heater Application

Wattco_duct_heater_Kilowatts_chart

Choosing the appropriate duct heater for your requirements is a question of the temperature you need to reach and how quickly it must be attained. Consulate the chart pictured to determine the Kilowatts required for your application.

Duct Heaters and Different Heating Coils

We’ve already mentioned that within the category of duct heaters there are different options for elements: open coil, tubular, or finned tubular heating elements. Below we will cover each type of element and elaborate on its suitability depending on its application.

Open Coil Duct Heater

The open coil duct heater is a type of heater which has exposed coiled elements running horizontally or vertically across the plane of air movement. The coiled element in an open coil duct heater is similar to that found in a conventional space heater you may have at home.

duct-heater-construction-diagram

Open coil heaters are typically used in comfort applications such as heating an office or industrial space. Because they don’t need to operate in extreme conditions and aren’t exposed to hazardous materials, open coil duct heaters are cheaper to produce than their industrial counterparts.

The Different Applications For Flanged Tubular Duct Heaters and Unflanged Tubular Duct Heaters

Tubular duct heaters provide a great duct heating solution for a number of reasons. Chief among those reasons is their durability, strength, and ease of maintenance. They are also easy to install, don’t react too poorly to moisture or dust, and are flexible thanks to the variety of terminals they can be manufactured with.

Depending on your industrial requirements for the duct heater you may need one of two types of tubular heaters. Here are a few distinctions to keep in mind to help differentiate between the two and determine which one fits your needs.

Tubular Duct Heater

An un-flanged tubular duct heater is comprised of a duct bracket fitted with a tubular element similar in shape and construction to the heating element one might find on a screw plug heater or circulation heater.  Duct heaters with an unfinned tubular element are the least common and are only available for specially approved applications. Contact us for more information about procuring one of these specialized duct heaters.

Tubular elements in duct heaters are most often chosen when the heater needs to operate in an environment where an electrical shock is likely or if there is a potential for buildup of static electricity.

Finned Tubular Duct Heater

The finned tubular duct heater is the most popular duct heater manufactured by Wattco. It gets its popularity from its practicality and the wide range of applications it can be used for.  The tubular heater’s mechanical strength makes it a great piece of equipment for harsh conditions.

Differences Between Flanged and Unflanged Duct Heaters

The obvious difference between the two types of tubular duct heaters are the fins which can be seen around the heating element of the finned tubular duct heater. The fins which surround the tubular heating element maximize surface area and therefore allow the heat generated by the element to dissipate faster than it’s un-flanged counterpart is able to do. This quality prolongs the life of the heating element by dispersing the heat over a larger surface area. Low-moisture areas require steel fins, and they provide superior heat transfer over stainless steel fins. However, stainless steel fins have their own advantages. Namely, stainless steel fins are far more rigid and therefore more suitable for processes which involve vibration.

Duct Heater Construction

Depending on the type of heater you need and its regular maintenance needs, you will require one of two duct heater frame constructions: Insert type or flange type.

Insert-Type Duct Heater

side-view-of-Wattco-inster-duct-heaterThe insert type duct heater slots into an opening in the side of the ventilation duct as pictured. The terminal housing protrudes from the vent and provides easy removal for maintenance or replacement.

Flange-Type Duct Heater

Flanged duct heaters slot into the vent to connect two vents which converge. Both the insert duct heater and flange duct heater can have a housing oriented at the side or bottom. They can also be used in tandem as required.

Side_View_of_Watto_flanged_Duct_heater

To ensure your heater is sturdy and long-lasting we build a frame from thick galvanized steel, also preventing rust as much as possible. Our mounting flanges are designed for fast, easy, secure insertion into the heating duct.

Factors Affecting Tubular Duct Heaters

Wattco builds duct heaters to be as dependable and long-lasting as possible, but there are a few factors which can affect the heater’s performance. These variables are the watt density used with the heater and the material the sheath is made of.

Watt Density

The advantage of having a high watt density heater is that the duct heater can heat up quickly because the amount of wattage over the surface area of the element is high. If your application requires the fastest heating time possible, a high watt density is required. Unfortunately, due to the laws of physics concerning thermodynamics, the higher the watt density the more likely the lifespan of the unit will be shortened.

Material of Tubular Duct Heater Sheath

The material chosen for the duct heater’s sheath is of critical importance when making a decision for two reasons.  First, the sheath material must be chosen based on the temperature of the application it is intended for. The second factor depends on how corrosive the atmosphere is where the duct heater will be operating. An appropriate material must be chosen to sustain the corrosive qualities of the air. A Wattco representative can help you determine which material is right for your application depending on how corrosive the environment is. You can also consult the table below for information on the sheath material you need based on the temperature air will reach in your process.

Sheath Material Operating Temperature in Fahrenheit
Steel 750 ℉
Copper 350 ℉
Incoloy 1500 ℉
Stainless Steel 1200 ℉

Duct Heater Applications

Duct heaters have a range of applications both commercial and residential. While open coil duct heaters are often used for comfort applications, such as heating an industrial workspace or office, tubular heaters have a stronger construction and can be used in more adverse environments.

Duct heaters can be broadly separated into two categories of application. Air duct heaters are used primarily for air-flowing ventilation systems and comfort-heating applications (HVAC).  Process duct heaters are mainly used for industrial process heating applications, for example in ovens that require re-circulated air or forced circulation.

Below is a table listing some of the more common applications for which Wattco provides duct heaters.

Heat Treating Forced-Air Comfort Heating
Booster Air Heater Multi-Zone Reheating
Resistor Load Banks Air Drying Operations
Core Drying Air Preheating
Heat Pump Auxiliary Systems Annealing
Air Handling Equipment Fan Coils
Terminal Reheating Return Air Heating

Maintenance for Wattco Duct Heaters

Maintenance tasks for duct heaters can range from quick and simple to long and arduous, depending on your heater and application. Duct heaters in hazardous environments or bearing a heavy workload will require the most work. However, due to Wattco duct heaters’ efficient design and construction, they are easy and safe to remove and inspect.

If you or your staff have identified the problem, Wattco can supply replacement components and provide further information. Wattco reps can also assist in troubleshooting the problem. Wattco builds heaters with manual power shut-off so the heater can be safely removed for cleaning or replacement.

The Wattco Duct Heater Difference

What makes Wattco’s duct heaters different? Our strong commitment to quality assurance, years of design and development, and refined manufacturing process all contribute to some of the best duct heaters on the market today. Wattco is also willing to accommodate special needs and custom projects whenever possible, working together with the client to find an efficient solution.

Our clients trust our half-century of experience for producing quality products and continually striving to improve materials, design, and construction. Wattco is as transparent as possible with our clients and remains available for support, maintenance, and information well beyond the sale.
Wattco customers also prize our customer service and recognize we are the only company in our industry which offers quotes for a project in 24 hours and fast shipping. Contact us to experience the difference for yourself.

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