Air often moves through buildings in waysno one intended or expected. No oneplans for air to come down the chimney, spillingthe products of combustion into occupiedspace. No one plans for ventilating air togather moisture and particles by flowingthrough a crawlspace before entering thebuilding. No arrows on drawings indicate thatair should flow from the boiler room throughutility chases until it reaches the top floorwhere it enters occupied space through gapsaround pipes and conduits. And yet airflowslike these occur in nearly every building.