The present invention relates to a device and method for conserving heat in a combustion chamber having a supply device comprising a tube and being arranged for supplying a fluid into the combustion chamber, the method comprising: providing the tube in the combustion chamber, the tube having a lateral surface, a first end with a first end surface, and at least one aperture through at least one of said surfaces, said tube, led by said first end, extending into the combustion chamber through a through hole in a wall of the combustion chamber; circulating a cooling liquid in the tube and in a coolant conduit loop outside of and connected to said tube for cooling the tube; cooling the cooling liquid with a gas flowing past the coolant conduit loop such that heat is exchanged from the coolant conduit loop to the gas; and introducing the heated gas into said combustion chamber.