The present invention relates to a floating structure comprising at least a closed space (10), a hull in the shape of a concrete cofferdam (12) having an external delimiting surface intended to be exposed to surrounding water, and a function for heating of the space comprising a heat pump connected to a closed circuit for circulating heat transport medium. At least one collector hose (14) for the circulating heat transport medium is provided in recesses in the concrete such that the cross section of the collector hose is located entirely within an outer outline of the cofferdam, whereby heat from surrounding water is absorbed by the collector hose and used for heating of the space. The invention also relates to a method of moulding a concrete cofferdam (12) adapted to be a hull of a floating structure.