Abstract: Method and apparatus to improve the energy yield of a reaction, particularly a combustion process. When used in a heating system in which fuel is burned, a burner sprays fuel and combustion supporting gas, preferably air, into the reaction zone inside a combustion chamber. An electromagnetic radiation of which the frequency range is 8800 Mc/s .+-. 10% corresponding to the maximum motion which may be imparted to the reactants of the molecules is directed at the reactants, by an antenna whose axis intersects the axis of the burner inside the reaction zone. A dissociable substance, preferably water with a surface active agent, is used as an additive and injected towards the reaction zone. An electrostatic field is provided around the spray of fuel leaving the burner by a metal ring at a potential of 300 to 25,000 V.