Many buyers ask us for an “immersion heater” when they need a tubular heater, or the other way round. The two are closely related, so the confusion is understandable. Here is a simple explanation.
What is a tubular heater?
A tubular heater is the basic building block of many industrial heaters. It has a nickel-chrome resistance coil placed in the centre of a metal tube. The space around the coil is filled with high-grade magnesium oxide (MgO) powder, and the tube is then compacted (swaged). The MgO insulates the coil electrically but conducts heat very well to the tube.
Because the tube can be bent into almost any shape, tubular heaters are used for:
- Air and gas heating – in ducts, ovens, dryers and hot air generators (often with fins added)
- Surface heating – clamped onto plates, platens and dies, or placed in machined grooves
- Radiant heating – spaced away from the work
- Liquid heating – when fitted with a flange or screw plug, the tubular heater becomes an immersion heater
- Casting into metal – for hot plates and heated blocks
Typical sheath materials are stainless steel, Incoloy and copper, in tube diameters roughly from 6 mm to 16 mm.
What is an immersion heater?
An immersion heater is designed to sit directly in the liquid it heats – water, oil, chemicals or solutions. In most industrial immersion heaters, the heating elements are tubular heaters, mounted on:
- a screw plug (for smaller tanks),
- a flange (for larger kW ratings and pressure vessels), or
- an over-the-side bracket (for open tanks where you can’t drill the wall).
So, an immersion heater is usually a set of tubular heaters plus a mounting and a terminal enclosure.
Key differences at a glance
| Tubular heater | Immersion heater | |
|---|---|---|
| What it is | A single heating element | A complete assembly for liquids |
| Heats | Air, surfaces, liquids, metal | Liquids only |
| Mounting | Clamps, brackets, fittings | Screw plug, flange, over-the-side |
| Shapes | Straight, U, W, coil, custom | Usually hairpin elements on a head |
| Terminal box | Optional | Normally included |
How to choose for liquid heating
When heating liquids, the most important choice is watt density – how much power each square centimetre of the element surface puts out.
- Water can take a relatively high watt density.
- Oils and viscous liquids need a much lower watt density. Too high and the oil carbonises on the element, insulates it, and the element burns out.
- Corrosive chemicals need the right sheath – SS 316, Incoloy, titanium or other materials depending on the chemical.
Also decide the required kW (see our guide on calculating heating power for a tank), the voltage and phase, the mounting type and whether you need a thermostat or thermowell.
How to choose for air heating
For air, consider air velocity and outlet temperature. Finned tubular heaters give more surface area and run cooler, which improves life in forced-air applications such as duct heaters and hot air generators.
Get it made to your requirement
Thermosys Technologies manufactures tubular heaters, finned heaters and immersion heaters in Narhe, Pune, with in-house swaging, MgO filling and bending. Tell us what you are heating and we will suggest the right design.