Fluid injection in a pipeline is commonly modeled solving the momentum, energy and mass balance equations averaged across the section of the pipe. Thus it is a non-linear problem, this approach computationally is costly. Inspired by the relation between head losses and water velocity in channels, we proposed a generalization of Manning’s formula for the case of a multiphase, compressible non-isothermal fluid system to avoid solving the momentum equation. We model the non-isothermal injection of CO2 in a vertical pipe to assess the validity of the proposed formulation. We consider different inflows and temperatures of the injected fluid, and take into account the heat exchange with the pipe’s walls. Temperature, density and mass fractions are computed using the Span andWagner equation of state.