Last updated on April 22nd, 2025 at 06:22 am

Watt density refers to the measure of power from a heating element divided by the heated surface area of the element itself. Of course, that’s just the surface (excuse the pun) of this concept. It has major implications when choosing a heater and its components (i.e., flanged elements). This post will explain how watt density works, how to calculate it, and how it factors when purchasing certain heating elements.

Clarifying watt density

Industrial operators use watt density to help determine the most effective heating elements (and heaters) for their application. As mentioned at the article’s outset, watt density is the heating element’s power divided by its surface area that’s actively heated. The calculation equation looks like this:

Watt Density = Power / Surface Area = Heat Flux

Watt density is typically expressed in watts per square inch, although in some countries, the unit is watts per square millimetre.

Importance of calculating watt density for industrial applications

Watt density essentially predicts a heating element’s efficiency compared to other options. Calculating watt density helps you identify whether a heating element will produce heat adequately and its potential lifespan. Essentially, it helps answer the question of whether it will be a suitable choice or not.

Of course, greater heat efficiency and a longer lifespan are ideal for most (if not all) industrial applications. But the right watt density for your operation depends on the process and the heat required to sustain an ideal temperature at a cost-efficient rate.

Understanding the watt density of a heating element can help you determine whether a specific heating method is superior (or not). For example, industrial staff may determine whether conduction, irradiation or convection is better for a particular application. The equation can also help determine whether a specific element is beneficial, such as duct heaters, open coil, tubular or finned-tubular flanged element.

The balance between low vs high-density flanged elements

Although ideal watt densities vary considerably depending on the application, extremes can also be problematic. When the watt density is too low, the heater’s price will be high. Ultimately, a heater of this nature is not cost-effective since its price may be too high for its limited heating capability.

Contrarily, a watt density that’s too high can lead to equipment failure. In such instances, what happens is that the heat overwhelms the element, leading to damage or complete burnout. That’s why it is common to choose the one with a lower watt density for safety when deciding between one of two heating elements.

Remember that watt density can vary significantly based on the size of the heating element and the material used in its sheath. Take, for example, a 4” low-density steel sheath and a 4” high-density Incoloy sheath.

Both have the same diameter and can both weigh 150 lbs, yet the Incoloy sheath has a watt density of 65.8 w/in2 compared to the steel sheath, which has a density of just 10 w/in2. Size and material should be deciding factors when choosing a heating element for your industrial application.

Wattco recommendations for watt densities and flanged elements

Watt density is a crucial factor that helps you choose the most efficient flanged elements (and, by extension, flanged heaters). That ultimately enables you to save time, cut costs, and optimize your heating process while safeguarding your equipment.

Here at Wattco, we offer a range of options for flanged heaters and elements so that you can find a suitable unit for your application. Our representatives can also provide insights on the ideal watt density for your application based on its requirements.  Get a quote or request more information about a flanged heating element today.

Could a Wattco staff provide a sample calculation of watt density.