As others sate, LPG is higher pressure, higher energy, and needs a different fuel/air mix than Natural Gas. The regulator keeps it at the right pressure so you should be 'safe' at that point, but where it gets complicated is the fuel/air mix that is achieved using a venturi. That is a finely tuned system designed for a given input pressure and density to mix the right amount of fuel with the right amount of air -- and the whole thing is regulated to the hole size in the burner -- Those holes act as a fire-dam keeping the flames outside of the burner. Wrong hole = burnt up and/or blow'd up burner. Long story short: Get the conversion. its cheaper, safer, and gooder.