Watt Density – Watt is it?

Watt Density can be overlooked in the search for a heating element, but it can be a vital component in reducing early failures.

If it’s glowing that’s a good thing right?

Not always!

By definition, Watt Density is the output of the heating element or the resistor in watts per square inch. Essentially, the amount of heat/energy coming from a specific surface area.

Finding the Watt Density for our 8mm diameter electric elements is a simple calculation – Dividing the wattage of the given element by the length of the hot section.

Length of hot section

Here are a few quick examples

Essentially the more surface area, the more space the ‘watts’ have to move around for heat transfer.

Different watt densities are required for different types of applications, so it is important for the performance of your application to understand the best watt density level. If the appliance is operating at a higher level than recommended, this can lead to early failures of your elements.



36 – 6 = 30

2000/30= 66.66

67 W/in2

If you have a Bain Marie element that is 36″ 2KW 240V 3″c/e – the Watt Density is sitting at around 67 W/in2. So looking at our guide, it would need to be completely immersed in water during operation. If the element is running on power out of water slightly or simply in air instead, there would be a high risk of failure or the element “blowing”.

Below is our basic guide to Watt Density in relation to applications. We have based this off of a range of general figures to create a ladder.

W/in2Heating Element Application Guide
94Immersed Only
83Immersed Only
73Immersed Only
63 Immersed / High Airflow / Machined
52 Immersed / High Airflow / Machined
42 Equivalent to Grill / Radiant Orange
31 Glow
21Colour Change
8-10 Little / No colour change – Still Air
1-7 Black Heat
2 hot cupboard heating Elements side by side - both have been formed to fit within the same space. The left hand side is the original customer sample which used a smaller length tubular heating element and encountered frequent fails. The right hand side shows TPFAY's design looping the element back around the circle to double the surface area and stay within the compact space within the customer application.

Limited space available in your application? Our team can work with your available space to ensure our heaters provide the maximum surface area while staying compact. Reducing the risk of early failure, our designs are built for longevity.

If you would like to know more about the Watt Density of your application or need some help deciding what heater is best for you, get in touch with our team today.