A support for a substrate processing chamber has upper and lower walls that are joined by a peripheral sidewall to define a reservoir. A fluid inlet supplies a heat transfer fluid to the reservoir. In one version, a plurality of protrusions extends into the reservoir to perturb the flow of the heat transfer fluid through the reservoir. In another version, the reservoir is an elongated channel having one or more of (i) serpentine convolutions, (ii) integral fins extending into the channel, (iii) a roughened internal surface, or (iv) a changing cross-section. A fluid outlet discharges the heat transfer fluid from the reservoir.