Crash Course on Duct Heaters

What are Duct Heaters? It’s easy to understand what duct heaters are just by considering their name. Simply put, duct heaters are installed in the ducting ventilation systems. The most common way they’re installed is through the sidewalls. The application of duct heaters in the sidewalls allows them to heat the air in the duct as it flows in and around the heating element of the open coil.   More often than not, duct heaters can be used for a variety of purposes. Some of these applications include HVAC systems and numerous industrial applications. The design of a duct unit is determined by the intended use and function of the air system.  

Shapes and Sizes     Duct heater using tubular elements

The shape of the duct heater varies with each unique situation and function. More commonly, they’re manufactured in a square shape but rectangular heaters are equally as common when custom-built heaters are required. Round duct heaters are also good options when the situation arises.  

Types of Circuits  

Three and single-phase duct heaters are available in the market with the voltage capacity of around 600V. The watt quotient of the duct heater is also subject to multiple variations. Resulting in a variety of duct heaters present in the market, ranging from less than 1kW to a maximum of around 175kW.     As far as the circuit considerations of a duct heater are concerned, they can be done in multiple stages. Each stage itself represents a standalone circuit:  

  • The powering of each stage may be done independently and separately to allow for various levels of heat output at each stage.
  • The wiring of each of stage must be done independently allowing the minimization of the amp load. This is likely to aid the smaller cable gauges. Yet, it is important to realize that despite the independent wiring, they may continue to operate in the same way.

Watt density  

Watt density, in this context, means the density of the heater coil watts per square inch of the coil wire’s surface area. Usually, it’s important to note that the watt density is not specified by industrial users, although they can limit it in terms of not to exceed a certain limit of watt density. When it comes to watt density, the lower the number the better it is assumed, since the coil life is inversely related to it.  

Flow Rates  

The flow rates of a duct heater are calculations that are based on the area of the duct and the velocity of the air. A lack of adequate airflow in duct heaters reduces the duct heaters effectiveness. This is because a lack of airflow will result in breakage and coil overheating in duct heaters.    

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