The thermal efficiency of a forehearth is assessed form data derived from the 9 point grid provided by the equalizing section tri-level thermocouples. Several formulas exist that express the absolute differences between the 9 point temperatures as a percentage efficiency value. Some formulae use all 9 points and, if all were at identical temperatures the efficiency value would be 100%. Other formulae employ only the 3 central thermocouples points and the right hand and left hand side
bottom thermocouple points.