I am solving the heat equation in a non comercial C++ finite elements code with explicit euler stepping, and adaptive meshes (coarse in the boundaries and finer in the center). I am aware the CFL condition for the heat equation depends on dt/h**2 for the 1D, 2D, 3D case. When I solve the equation in 2D this principle is followed and I require smaller grids following dt<h**2. But in 3D the problem seems to be requiring finner and finer grids as I decrease the timestep in what appears to be a dt/h**3 behaviour. Does anyone have an idea what could be happening? is the CFL no longer valid in FEM and 3D? What other factors could be influencing?