Particle formation in semiconductor fabrication process chambers is reduced by preventing condensation on the door plates that seal off the process chambers. Particles can be formed in a process chamber when reactant gases condense on the relatively cool surfaces of a door plate. This particle formation is minimized by heating the door plate to a temperature high enough to prevent condensation before flowing reactant gases into the process chamber. The door plate can be heated using a heat source, e.g., a resistive heater, that is in direct contact with the door plate or the heat source can heat the door plate from a distance by radiative or inductive heating. In addition, the door plate can open to allow loading and unloading of a wafer load. As it passes flanges near the door plate, the wafer load can transfer heat to those flanges. To prevent overheating, the flange is provided with a coolant-containing channel having walls that are spaced from the flange by O-rings. The spacing of the channel walls to the flange can be varied to vary the amount of thermal contact and cooling achieved using the channels.