Heating element component

Heating Element Construction

A typical tubular heating element consists of several layers.

1 — Resistive Wire

Usually made from Nichrome (NiCr alloy) which has high electrical resistance and good high-temperature stability.

2 — Electrical Insulation

Magnesium oxide (MgO) powder is used to electrically insulate the resistive wire while allowing efficient heat conduction.

3 — Metal Sheath

The metal sheath is the outer tubular casing of the heating element. It serves two main functions: protecting the internal components of the element and transferring the generated heat to the surrounding water.

The sheath must have good thermal conductivity, corrosion resistance, and mechanical strength to operate reliably in hot water environments.

Common sheath materials include:

• Stainless Steel

Typically used for dry heating elements or applications where the element is not directly exposed to water. It offers good corrosion resistance and durability.

• Copper

The most commonly used material in electric water heaters. Copper provides excellent thermal conductivity and performs well when the heating element operates directly immersed in water.

• Incoloy Alloys

High-temperature nickel-based alloys used in demanding environments such as chemical tanks or highly corrosive water conditions. They provide superior resistance to corrosion, scaling, and high temperatures.

4 — Terminal Pins

The terminal pins provide the electrical connection between the heating element and the external electrical circuit, typically through the thermostat and the internal wiring of the water heater.

Heating elements are commonly manufactured with two types of electrical terminals:

Screw Terminals

Electrical wires are connected using ring or fork connectors that are secured with nuts or screws. This type provides a strong and reliable connection and is often used in industrial heating elements.

Female Spade Terminals

Flat blade terminals that allow quick electrical connection using push-on connectors. In most domestic electric water heaters, the heating element uses 6.3 mm female spade terminals (¼ inch blade terminals). The rod thermostat connects to these terminals using 6.3 mm male spade connectors.

The spade terminal design allows fast assembly, easy replacement, and reliable electrical contact inside the heater’s electrical compartment.

5 — Mounting Flange or Thread
Allows the heating element to be installed in the tank wall. There are two common types:

Flange Type (Bolted):
A normal flange fixed to the tank using M6 screws, with a heating element gasket to ensure proper sealing.
Threaded Type:
A screw-type flange with a standard thread, usually G 1¼ in (BSP), allowing direct installation into a threaded tank opening using gasket to ensure proper sealing

Heat Transfer to Water

The heat produced inside the element travels through several stages:

Resistive wire generates heat
Heat passes through MgO insulation
Heat transfers through metal sheath
Water absorbs heat by convection

Efficient heat transfer requires

• good thermal conductivity
• proper element surface area
• adequate water circulation

Heating Power, Surface Loading, and Heating Time Calculation

Key performance parameters of the heating element include heating power, surface loading, and heating time.

These parameters are calculated based on standard heat transfer and energy balance equations. For detailed methodology and formulas, refer to the Heating Power Calculation page and use our engineering tool: Heating Element Power Calculator and heating time calculator .

Heating Power (W): Determines the required heat input to raise water temperature.
Surface Loading (W/cm²): Indicates heat flux over the element surface and its impact on durability.
Heating Time (min): Time required to heat a specific water volume between two temperatures.