Every lehr must allow ample time for heating and cooling glass, in particular when the planned values are exceeded. This is done by allowing heating and cooling zones that are as lang as possible.

Good lehr performance is about equalizing the variations in Ioad i.e. volume of glass and temperatures. A good response comes first from a sufficient firing and ventilation capacity that adequately respond to temperature deviations from the target curve. The more thermo-couples readings, the more precisely controlled is the temperature (Annealing) curve. The more burners, the more effective the control of temperature.