A buoyancy-capture principle is firstly revisited as the most important fluid dynamics mechanism in kitchen range hoods. A recent new derivation of the capture efficiency of a kitchen range hood, which eliminates the inconsistencies and inadequacies of existing derivations, shows that the capture efficiency equals the ratio of capture flow rate to total plume flow rate in a confined space. The result is applied here, together with the buoyancy-capture principle, to derive a simple formula for determining capture efficiency. A computational fluid dynamics (CFD) program is adapted to study the capture efficiency of range hoods in a residential kitchen and the predicted results are used to evaluate the accuracy of the simple formula. It is shown that the simple capture efficiency model performs reasonably well for the range hoods considered in this paper.