The invention provides an apparatus for generating heat and transferring the heat to a heater head of an external combustion engine, preferably, a Stirling engine. Fuel and air are introduced into a combustion chamber and mixed to form an air/fuel mixture. The air/fuel mixture is combusted over a combustion catalyst positioned in physical contact with a heat spreader, which itself is positioned in physical contact with a heat acceptor surface. The heat acceptor surface is secured in thermal communication with the heater head. Depending upon the design of the heater head, heat flux from the heat acceptor surface into the heater head may occur radially or non-radially.