The hot oil boiler has been manufactured as radiation-type; having spiral oil pipes, from seamless steel boiler tube, wrapped up with one-, two- or three-way screw-steps depending upon the capacity and the velocity values, the flow of the gases have been designed as three-directional. The most critical place in all the installment is the boiler serpentines, since this is the hottest place. The other parts of the installment are less hot as compared to here, due to this reason, the velocity of oil at the serpentines have been adjusted according to the number of tubes openings at the manufacture. Since all the oil inside the system passes from the boiler spirals, the flow is fully under control. Thus, the safely heating of the heat carrier is obtained. There is no kind of isolation at the burning cell.