A tank (1) and heat exchanger combination heat a heated fluid in the tank (l). A heat transfer tube (10) is attached to a heat exchanger flange (20) for providing a heat generator fluid for transfer of heat to the heated fluid in the tank. Pipe structures (30A, 30B) are attached to the heat exchanger flange (20) for connecting the heat transfer tube (10) to a source of the heating fluid. A method of heating a tank (1) by connecting the heat exchanger flange (20) to a tank flange (60) provides an efficient and safe heating process.