NOVELTY - The installation comprises a room (3) to be heated and a composting rack (2) disposed outside the room to be heated. The composting rack comprises a floor (20) such as concrete flagstone, and a conduit (4) comprising a fluid circulation portion (41) forming a drain perforated along its length. The conduit comprises a movement portion forming a heat exchanger having a heat exchange surface with an area to be heated. The installation further comprises a unit for forced circulation of fluid from the fluid circulation portion to the movement portion of the heat exchanger such as a fan.    USE - The installation is useful for recovering heat produced by composting waste.    ADVANTAGE - The installation is capable of economically and simply recovering the heat produced by composting waste.    DETAILED DESCRIPTION - The installation comprises a room (3) to be heated and a composting rack (2) disposed outside the room to be heated. The composting rack comprises a floor (20) such as concrete flagstone, and a conduit (4) comprising a fluid circulation portion (41) forming a drain perforated along its length and located under or at outcrop of a face of the floor directed towards an interior of the rack. A part of the perforations communicates with the interior of the rack. The conduit comprises a movement portion forming a heat exchanger having a heat exchange surface with an area to be heated. The installation further comprises a unit for forced circulation of fluid from the fluid circulation portion to the movement portion of the heat exchanger such as a fan, and a unit for gas waste processing, and a unit for re-injection of a gas effluent treated in the room. A surface area of the heat exchange surface of the movement portion is greater than 0.15 m2 per 1 m3 of useful volume of the rack. The heat exchange surface of the movement portion is present in direct contact with ambient air of the room to be heated. The forced fluid circulation unit is located downstream the room to be heated. The room to be heated is of greenhouse type. The fluid circulating through the conduit is the gas effluent from a passage of an outside air trap through a composting material of the rack. The conduit is provided with a fluid evacuation unit positioned downstream from the movement portion of the conduit. A wall of the fluid circulation portion forming the drain has a thermal conductivity of less than or equal to 0.1 W/m/ degrees K. A wall of the fluid circulation portion located between the rack and the room has a thermal conductivity lower than that of a wall of the movement portion of the conduit. The rack presents an air intake in an upper part of the rack. An INDEPENDENT CLAIM is included for a method for heating a room to heat the installation.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of an installation for recovering heat produced by composting waste.    Composting rack (2)    Room (3)    Conduit (4)    Floor (20)    Fluid circulation portion. (41)