Aside from any special fire objects that might be found, a picture of fire does the trick:
1: Get the picture
2: mask out the non-flame part - feather the mask for good flame edges.
3: place several thin walls in the fireplace - overlapping and curvy - be artistic.
4: Apply the fire image to the walls as a material. Adjust height of image map with the "Align 3D Texture" command.
5:Rotate fireplace control knob for authenticity. If the viewer sees a fireplace set to "off" and flames, too, they will know it is fake.
6: A spark screen in front of the flames scrims the flame image for more realism.
Dwight Atkinson