A method for the production of product gas from carbonaceous feed material, comprising the steps of: a) heating a gaseous medium by thermal energy; b) transporting the heated gaseous medium to a first reactor containing carbonaceous feed material; c) heating the carbonaceous feed material in the first reactor to a temperature of at least 400 °C by means of the heated gaseous medium so as to form components of a product gas, directing the gaseous medium of step c) to a second reactor containing carbonaceous feed material and forcing the gaseous medium through the carbonaceous feed material of the second reactor; d) withdrawing at least part of the product gas after the gaseous medium has passed the carbonaceous feed material of the second reactor, and e) recirculating the rest of the gaseous medium to the first reactor thereby continuing the production of product gas through steps (a)-(d); f) continuing the circulation of gaseous medium from the first reactor to the second reactor until a set point defined by a desired value of a temperature measured in the layer of charcoal and/or carbonaceous material in the second reactor has been reached and/or until a pre-set time has been reached; and then g) reversing the direction in which the gas is circulated by means of a system constituted of at least one fan (4, 4a,4b;) providing flow in one direction and a valve system (34,35,36,37;31,32) whereby the withdrawal of at least part of the product gas in step d) takes place after passage of the carbonaceous material of the first reactor and the rest of the gaseous medium is recirculated to the second reactor in step e); wherein the heating performed in step (a) is provided by an electrical source. a) heating a gaseous medium by thermal energy; b) transporting the heated gaseous medium to a first reactor containing carbonaceous feed material; c) heating the carbonaceous feed material in the first reactor to a temperature of at least 400 °C by means of the heated gaseous medium so as to form components of a product gas, directing the gaseous medium of step c) to a second reactor containing carbonaceous feed material and forcing the gaseous medium through the carbonaceous feed material of the second reactor; d) withdrawing at least part of the product gas after the gaseous medium has passed the carbonaceous feed material of the second reactor, and e) recirculating the rest of the gaseous medium to the first reactor thereby continuing the production of product gas through steps (a)-(d); f) continuing the circulation of gaseous medium from the first reactor to the second reactor until a set point defined by a desired value of a temperature measured in the layer of charcoal and/or carbonaceous material in the second reactor has been reached and/or until a pre-set time has been reached; and then g) reversing the direction in which the gas is circulated by means of a system constituted of at least one fan (4, 4a,4b;) providing flow in one direction and a valve system (34,35,36,37;31,32) whereby the withdrawal of at least part of the product gas in step d) takes place after passage of the carbonaceous material of the first reactor and the rest of the gaseous medium is recirculated to the second reactor in step e);