The heat transfer processes in the growth of single crystals in a verneuil plasma torch were investigated. Heat transfer from the plasma to the crystalline boule was enhanced to a substantial degree by recombination of dissociated diatomic gases in the region of the boule tip. Boule tip temperatures were affected by the location of the boule in the plasma, distance of the boule from the powder probe, the feed rate and grain size of the powder being fed, the rf plate power of the generator, and the powder gas flow rate. Boule temperatures depended critically on heat loss by radiation from its side. It is predicted that refractory crystals require higher plasma input power as the boule becomes longer, if crystal growth rate is to be maintained.