A heater for fluid flow components. The heater has heat transfer surfaces that engage the component. The transfer surfaces are mounted on jaws that are movable to engage the component. The jaws have massive portions that act as heat reservoirs to maintain a constant temperature in spite of rapid cooling when gas is allowed to expand freely from the component. The jaws are heated by electrical resistive heating elements that are sealingly mounted within the massive portions. The sealing engagement allows the heater to be used in hazardous environments.