Help next to a bar-b-q. Does a diffuser transport the place of lava rocks? I am a first time gas bar-b-q user and am feeling...

I am a first time gas bar-b-q user and am feeling incompitent beside the process. If you do use lava rocks do they go ontop or below the diffuser. Thanks for any help out
Answers:    If you have a diffuser ( resembling one brands "flavor Bars " ) they are designed to be used without lava rock or earthen briquettes. If it has what looks similar to just a regular grate you should use them. On top of the grate logically.
On top. Lava rocks help spread the warmth out and also maintain it after the grill is past its sell-by date (for keeping stuff warm). It also catches grease droppings.