Do u really guess that they have different heights?
Who have else than u written
Even official sources cannot guarantee correct height data! . These aeronavigational agencies took this data by land-surveying methods.
But 270 m is the common height for many chimneys.
http://skyscraperpage.com/cities/?buildingID=91285
http://skyscraperpage.com/cities/?buildingID=91284