  We construct an effective model for the QCD equation of state, taking into
account chiral symmetry restoration as well as the deconfinement phase
transition. The correct asymptotic degrees of freedom at the high and low
temperature limits are included (quarks $\leftrightarrow$ hadrons). The model
shows a rapid crossover for both order parameters, as is expected from lattice
calculations. We then investigate the thermodynamic properties of the model at
$\mu_B=0$. All thermodynamic quantities are in qualitative agreement with
lattice data, while apparent quantitative differences can be attributed to
hadronic contributions and excluded volume corrections.
