This one is quite popular but in case you don't know how to do the fire. Start a new grayscale image, 340x120 for example. black background, white foreground

Rotate image 90 degrees CW Image/Rotate/90 CW
Use Filter/Stylize/Wind... twice with settings Wind/Right.
Use Filter/Stylize/Diffuse... with default settings. Image/Rotate/90 CCW

Fine, now Filter/Blur/Gaussian Blur with setting of 2.0

Use Filter/Distort/Ripple with default settings

Now, Mode/Indexed Color
Mode/Color Tables choose Black Body...

© 1996 Nick Ustinov.