The solar chromosphere is a region where the thermodynamics are out of equilibrium, and realistic values of temperature and electron densities here are difficult to obtain. Hydrogen, being the most abundant element in solar gas, dominates the equation of state. When doing time dependent multi-dimensional numeric modelling, the hydrogen state should therefore be treated with care - that means solving its rate equations. An algorithm that solves the rate equations with fixed radiative rates and couples hydrogen occupation numbers to the equation of state has been adjusted to fit the new stellar atmosphere code Bifrost. The method is described and results from a 3d test simulation are presented.