The invention relates to a device for storing heat, comprising a heat storage medium which absorbs heat in order to store heat and releases heat in order to use the stored heat, and a container for holding the heat storage medium, the container being closed by a gastight cover, and the device comprising volume compensation means in order to compensate for a volume increase of the heat storage medium (3) due to a temperature rise and a volume decrease due to a temperature reduction. The invention furthermore relates to a method for storing heat, in which heat is transferred to a heat storage medium in order to store heat or heat is discharged from the heat storage medium to the heat carrier in order to use the heat, the heat storage medium being held in a container which is closed by a gastight cover, wherein a volume expansion of the heat storage medium (3) is compensated for by a volume increase of the container (1) or by heat storage medium (3) flowing out of the container (1) into a buffer container (21; 63, 65), and a volume decrease of the heat storage medium (3) is compensated for by a volume decrease of the container (1) or by heat storage medium (3) flowing out of the buffer container (21; 63, 65) into the container (1).