In this paper, electricity generation using very low bandgap InGaAsSb thermophotovoltaic (TPV) cells whose bandgap is 0.53 eV was investigated in a gas-fired furnace system where thermal radiation was emitted from a metal alloy emitter. The electric output of the InGaAsSb TPV cells was characterized under various operating conditions. The cell short circuit density was measured to be 3.01 A/cm(2) at an emitter temperature of 1197 degrees C. At this emitter temperature, an electric power density of 0.65 W/cm(2) was produced by the TPV cells. Experimental results show that direct thermal to electrical energy conversion was achieved in a gas-fired heating furnace system. Such a system could be employed to form a micro-combined heat and power (micro-CHP) process where exhaust heat is utilized for home heating needs. The TPV integrated energy system provides an effective means for primary energy savings. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.