We present here a rational but simple asymptotic theory for the influence of homogeneous reagent consumption on heated surface chemical vapor deposition (CVD) rates, exploiting the fact that in most cases the overall activation energy of the homogeneous chemical reaction is large enough to confine reaction effects to a thin chemical sublayer embedded within the ordinary diffusion boundary layer. Explicit analytical results are obtained and illustrated for cases in which both heterogeneous and homogeneous kinetics can be represented by power-law/Arrhenius functions. Because of the large molecular weight disparities and high-temperature gradients prevailing in many CVD-systems we also allow for the Soret reduction of dilute reagent Fick transport to the hot surface. The resulting closed-form rate expressions provide rational quantitative criteria for ’vapor-phase ignition’ (VPI) in terms of the CVD-system parameters and the presumed ’known’ chemical kinetic parameters characterizing the vapor reactants. Conversely, armed with such a theory, one can use experimentally observed VPI conditions to infer the effective homogeneous kinetic parameters for the system in question-information not always : independently available. In effect, one uses the gaseous boundary layer as a ’flow reactor’, with the CVD-surface as a detector (albeit imperfect) of the surviving reactant. Our general results can be applied to specific film systems of current interest, with our present emphasis being the CVD of TiO2(s) [from TiCl4 or Ti(OC3H7)(4)(g) + O-2].