Interacting convection zones

3D Numerical simulations of convection zones separated by a stable layer (according to the Schwarzschild criterion) are presented. The compressible case is considered. We make use of idealized microphysics closely related to polytropes. Decreasing the importance of the separating stable layer by diminishing its vertical extent in a series of models we investigate how the two convection zones merge into one. In our parameter range it is the upper zone which increases in size and ultimately squeezes the lower convection zone more or less out of existence. Properties of various fluxes and other physical quantities are discussed.