The present invention discloses a heating and cooling system of a modular residential building at least comprising: a) a building framework, b) a number of flat modules (1.0), c) a number of front elements (6.04), d) at least two gable elements (6.03), e) at least one roof element (6.02), and f) a plurality of horizontal and vertical heating and cooling canals, where the building frameworks includes fastening means (5.02) for securing the flat modules (1.0) to the building framework with a horizontal and vertical distance between neighbouring flat modules (1.0) thereby creating cavities there between where cavities are utilized as the plurality of horizontal and vertical heating and cooling canals.