The Blender Made Easy channel shows a Blender Compositor trick for how to render fire with transparency.

A new tutorial from the Blender Made Easy Channel shows a trick for getting fire in Blender to render with transparency. Adding an opacity to a fire simulation is a little more complicated than it sounds. The tutorial covers how to create and simulate the fire, and then shows how you can get it to render how you intend.

“There is a little trick in the compositor that allows us to render fire.” “We basically mask out where the fire is and use that as the alpha.”