Hi- By coincidence I've just dug out my installation book and the requirements are
width-406mm (min)-480mm (max)
height-540mm (min)-590 (max)
depth-210mm (min)
hope this helps
J. Carpenter, October 2009
if its a used fire you shouldnt be installing it without instruction manual, if its a new fire, you'll have instruction manual. The manual will specify clearances and distances.