Abstract: A flow-through heater for heating a fluid comprises: a high thermal conductivity conduit-defining body shaped to provide, within the conduit-defining body, a helical-shaped or spiral-shaped conduit that extends between an inlet port and an outlet port; and one or more heating elements operatively connected to an exterior of the conduit-defining body for providing heat to the conduit-defining body and to any fluid flowing through the conduit. Because of the high thermal conductivity of the conduit-defining body, all of the surfaces of the conduit-defining body that actually define the conduit contribute significantly to heating the fluid in the conduit. Each conduit-defining surface may contribute to heating the fluid in approximately equal proportion to its conduit-defining surface area.