How to Choose Watt Density for Your Electric Heater

Last updated on August 23rd, 2023 at 02:20 pm

Choosing the watt density to use with an electric heater varies. You must consider the application, the fluid being heated, the desired temperature, and the available power supply. Use this article as a guide to understanding watt density and choosing the right one for your electric heater.

Why does watt density matter?

Too high a watt density for the given electric heater can result in the heater failing, damage to the substance being heated, or damage to the equipment itself, all expensive and unwanted outcomes.


Watt density can range from five to over three hundred watts per inch squared. With such a wide range, it’s essential to get the right number that the electric heater or immersion heater requires.

The needs of the project help determine the necessary watt density in relation to the electric heater depending on the temperature and how consistent that temperature needs to be for the application to succeed.

Without the space to dissipate, consistently high temperatures and a medium with a low conductivity rate will cause overheating. This type of combination causes heaters to fail. Finding the right watt density maintains a heater’s ability to function properly.

How to choose the right watt density

Below are four things to consider when choosing watt density.

1. Sheath material

Sheath material is chosen based on the maximum temperature and corrosion resistance required. Metal material works for -300°F to 1,500°F. Copper is good for lower temperatures (350°F) and direct immersion heaters. Stainless steels (1,200°F) and Incoloy (1,600°F) work for corrosive solutions, high-temperature gasses, and cartridge heaters.

2. The maximum recommended watt density

The recommended watt density will depend on the substance being heated. Water and vegetable oil are well suited for high sheath watt densities, whereas petroleum oil and sugar syrups require lower watt densities. The incorrect watt density can carbonize or overheat the substance.

3. Watt density excess

If the substance has high conductivity rates, the heat will travel quickly so they can use high watt densities. Materials with low conductivity rates need lower watt densities as the heat doesn’t travel as efficiently. Watt densities that are too high cause heat transfer fluids and hydrocarbon oils to break down. Deposits form until a barrier stops the substance from traveling.

Use low watt densities when working with corrosive materials to control their chemical reactions. The effects won’t be as severe, or they’ll remain in the scope of the project when lower temperatures are used.

4. Additional wattage to control temperature gradients

In most thermal systems, the farther a substance travels from the heat source, the lower the temperature drops. To control the temperature gradient, some systems will use additional wattage. The higher watt density can be spread out over multiple heaters so the heat isn’t contained at extreme temperatures to one area, and rather spread out to maintain heat over a larger area.

If the heater has increased dimensions, the watt density requirement lowers. The more area a heater covers, the less wattage is required to heat the same amount of liquid. When possible, use lower watt densities as these lower heating element temperatures and prolong their life.

Electric heater guidance with Wattco

In these cases, there are many factors to consider to ensure an electric heater or immersion heater is functioning as best it can. Everything must be carefully selected, installed, and used to ensure the production of a material results in the intended resource. The slightest changes affect the outcome of a heated material. To manage these factors and choose the right watt density for your electric heater’s purpose, use the support and products offered by Wattco. We have the expertise and experience to guide you in the right direction and even offer custom manufacturing where needed. Contact us today.