Process knowledge is the key factor in establishing quality energy efficiency and integration solutions. Without process knowledge, engineers run the risk of oversizing, undersizing or creating non-feasible and potentially dangerous solutions. Resulting accidents can have the potential to cause massive damage to infrastructure, lives and the environment, especially in the refining and petrochemical industries (which can include fertiliser production). Data reconciliation offers a tool for increasing the certainty around measured flows and thermodynamic properties as well as calculating unknowns. A methodology is presented to model and reconcile steam networks in refineries and petrochemical sites.