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Fresh air enters a building through its air intake. Likewise, building exhausts remove air contaminants from a building so wind can dilute the emissions. If the intake or exhaust system is not well designed, contaminants from nearby outside sources (e.g., vehicle exhaust) or from the building itself (e.g., laboratory fume hood exhaust) can enter the building with insufficient dilution. Poorly diluted contaminants may cause odors, health impacts, and reduced indoor air quality. This chapter discusses proper design of exhaust stacks and placement of air intakes to avoid adverse air quality impacts. Chapter 16 of the 2001 ASHRAE Handbook-Fundamentals more fully describes wind and airflow patterns around buildings. Related information can also be found in Chapters 7, 14, 29, 30, and 31 of this volume, Chapters 12 and 13 of the 2001 ASHRAE Handbook-Fundamentals, and Chapters 24,25, and 30 of the 2000 ASHRAE Handbook-HVAC Systems and Equipment.