Abstract: A system for generating, storing and releasing heat comprises a tank surrounding a reservoir for holding a heat transfer fluid, heat releasing means in fluid communication with the reservoir for controllably releasing heat from the fluid to an object or space to be heated, and means for regulating flow of the fluid between the reservoir and the heat releasing means. A heat conductive fire chamber is disposed within and substantially surrounded by the reservoir, the system also comprising an air supply means for carrying combustion air to the fire chamber, and a heat conductive exhaust means for carrying hot exhaust gases through the reservoir. Access passageways are provided for fuel insertion and ash removal. Boiler tubes supporting the fuel as well as collecting heat from the fire chamber communicate with fluid in the reservoir. Shaker bars interspersed between the boiler tubes supporting the fuel may be actuated to agitate and more completely combust the fuel.