# How Do I Set a Heat Source?

| Date       | Category    |
|------------|-------------|
| 2025-06-17 15:50:52 | Heat |


The heat source is defined using the [HeatSource](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.HeatSource.html) object. Users can specify the volumetric heating rate, which can be uniform or spatially varying using a [SpatialDataArray](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.SpatialDataArray.html) object. The source can be applied to any structure within the simulation domain.

In practice, one often wants to model a heater with external current applied. To model this Joule heat source, we can calculate the volumetric Joule heat generation using

$$\frac{dP}{dV} = \frac{1}{\sigma}\left(\frac{I}{w_{heater}h_{heater}}\right)^2$$

where $\sigma$ is the electrical conductivity of the heater material, $I$ is the applied current, and $w_{heater}$ and $h_{heater}$ are the width and thickness of the heater, respectively.

For more information, please check our Heat solver technical [article](https://www.flexcompute.com/tidy3d/learn-center/technical-article/heat-solver-introduction/).