A method for installing a gas turbine assembly of a first type at a position of an existing power plant where previously a gas turbine assembly of a second type was installed on a foundation specially designed for said second type. The gas turbine assembly includes at least one housing, a compressor, a combustion chamber, a gas turbine, and a plurality of venting and removal lines guided along the exterior of the housing. Modifications to the venting and/or removal lines of the gas turbine assembly of the first type are carried out in a first step, and the modified gas turbine assembly is installed on the existing foundation in a second step.