The present invention provides a simplified heater design that is scaleable for equipment processing different diameter substrates and that can efficiently and economically process substrates to meet stringent film requirements such as film uniformity for fabricating high integration devices. The present invention is particularly useful for economically and efficiently producing integrated devices using increasingly larger diameter substrates, such as 12-inch (or 300-mm) diameter and even larger substrates. According to one embodiment, the present invention provides a heater assembly for use in a substrate processing apparatus. The heater assembly includes a metal pedestal including a surface for supporting a substrate, and a resistive heating element disposed in the metal pedestal. The heater assembly also includes a purge gas channel system disposed in the metal pedestal. The purge gas channel system includes a central purge gas inlet located substantially at a center of the metal pedestal. The central purge gas inlet is for providing a purge gas. The purge gas channel system also includes multiple radial purge gas channels radiating from the central purge gas inlet out toward a perimeter of the metal pedestal, and an annular purge gas channel formed in the metal pedestal at the perimeter. The purge gas channels form a substantially symetric pattern, and each of the purge gas channels are substantially the same length. In a specific embodiment, the assembly includes an annular purge gas channel coupled to the surface via multiple holes near the perimeter to provide a purge guide ring integral to the metal pedestal. Other embodiments of the present invention are also provided.