A method and design of providing high temperature heat for an endothermic gasifier without combustion includes flowing a stream of a first hydrocarbon gas sequentially through an annular plenum and a cylindrical plenum while heating the gas using electrical resistance immersion heating elements. These heating elements may be heated by three phase electrical power, minimizing the number of electrical leads emerging from the top of the heating elements. This method and design reduces the risk of extremely hot syngas exiting the gasifier damaging downstream fittings.