Dilution factors, obtained from scale-model tests in a boundary layer wind tunnel, were compared to empirical dilution factors obtained using the equations presented in the new (1989) chapter 14 of the ASHRAE Fundamentals Handbook. The use of this information in making design decisions is also discussed. The comparison illustrates the fact that while the empirical equations are useful in identifying a potential problem condition, building geometry can greatly alter the dilution. Consequently, a healthy level of conservatism should be maintained in setting stack heights or intake locations.