Abstract: A thermoelectric generating assembly for replacement of a heat exchanger mounted in a fuel-burning heater having electricity-consuming components includes a thermoelectric generator for supplying the electrical power requirements of the heater components and an adaptor portion for mounting the thermoelectric generator within the heater. The assembly possesses a size and shape which approximates that of the heat exchanger to be replaced and can be mounted within the heater in a manner like that in which the heat exchanger is mounted within the heater prior to removal. The method includes the steps involved in replacing the heat exchanger with the thermoelectric generating assembly.