For non-aluminum pans (unless you are cooking in liquid) adjust the flame so it is about half the diameter of the pan.
Foods cook just as quickly at a gentle boil as at a rapid rolling boil—in both cases the water temperature is 212 degrees. A high boil is used only to bring food to the boiling point; then lower the flame and finish cooking with a minimum flame.
EXCESS HEAT RESULTS IN HARD-TO-CLEAN GREASE AND STEAM DEPOSITS ON WALLS, CABINETS AND CEILINGS. WHILE THE FUEL IS OFTEN BLAMED FOR SUCH DIRT, THE REAL PROBLEM IS TOO MUCH HEAT AND/OR FAILURE TO COVER UTENSILS WHENEVER POSSIBLE.
HIGH FLAME
For instant heat needed to bring foods to a rapid boil.
MEDIUM FLAME
To brown and fry food.
SIMMER FLAME
To maintain gentle boil for boiling or steaming, cream sauces, gravies, puddings, etc.