Method for increasing efficiency during heating or cooling using an energy well (1) in the form of an elongated hole the bottom of which is arranged at a greater depth than its opening, where a cooling agent streams through the well (1) in a collector conduit (3) and is heat exchanged against the material surrounding the well (1). The invention is characterised in that a tube (301) runs down into the energy well (1) from above its opening and down along the energy well (1) towards its bottom, in that the end (303) of the tube (301) facing towards the bottom of the energy well (1) is open, in that liquid is supplied through the tube (301) so that the liquid thereby streams down and out into the energy well (1) through the open end (303) of the tube (301), in that gas bubbles (305) are supplied to the liquid streaming down through the tube (301), and in that the added gas bubbles (305) are so small so that they rise more slowly in the liquid than the velocity of the liquid at the supply point.