A heating unit comprising an electrically conductive substrate. A solid fuel layer comprising a metal reducing agent, a metal containing oxidizing agent and a binder is coated on a surface of the substrate, the solid fuel layer having a solid fuel surface spaced from the substrate. A first electrode coupled to the substrate. A second electrode coupled to the solid fuel surface. A power supply is configured to be selectively coupled to the first and second electrodes to provide a voltage between the metallic substrate and the solid fuel surface. The voltage acts to propagate an exothermic metal oxidation-reduction reaction without the use of an igniter.