The present invention relates to a single pipe collector for a heat pump installation. The collector comprises a pipe (12) intended for installation in a heat pump plant, in which pipe a heat transfer liquid circulates in a closed cycle for conveyance of heat that is absorbed from a heat source to a heat pump and return of the heat transfer liquid back to the heat source. The inward surface (14) of the pipe has an uneven surface structure that comprises indentations and/or elevations (16). The present invention also relates to heat pump plant comprising the collector.