<P> The chimney (smokestack or stack in American and Canadian English) is the part of a steam locomotive through which smoke leaves the boiler . Steam locomotive exhaust systems typically vent cylinder exhaust through the chimney to enhance draught through the boiler . Chimneys are designed to carry exhaust steam and smoke clear of the driver's line of sight while remaining short enough to clear overhead structures . Some chimneys included features to avoid dispersing sparks . </P> <P> The chimney was usually located above the smokebox at the leading end of the locomotive, furthest away from the driver's cab and firebox . The earliest locomotive chimneys were typically tall enough to sustain temperature - induced density difference draught through a fire - tube boiler while the locomotive was stationary; but following the example of Richard Trevithick's first locomotive in 1804, most designs diverted steam cylinder exhaust upward through the chimney to create a vacuum in the smokebox and accelerate airflow through the firebox while the locomotive was in motion . </P>

What comes out of a steam train funnel