Performance optimization of hygrothermal simulations – Parameter optimization of iterative solvers. Despite continuously enhanced computer hardware, running dynamic 3D hygrothermal simulations may still be a time-consuming process. The duration of simulations may be reduced by user-selected numeric parameters. However, the actual impact of parameters like maximum Krylov subspace, convergence coefficients etc. proves difficult to estimate. In the article different methods of reducing simulation speed are applied to two example cases. Starting with a grid sensitivity study the scaling of effort for different direct and iterative linear equation system solvers is discussed. Further, we investigate parameters influencing the iterative equation system solvers GMRES and BiCGStab in combination with ILU preconditioners. The tests are done with the software DELPHIN 6. The article concludes with recommendation for suitable initial parameter selection based on system size and a short methodology on how to optimize parameters based on collected solver metrics.