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Empire State Bldg. steam pressure
There is a lot of talk about the steam pressure in the Empire State Building being 2PSI. While this is true, it is important to understand that the building has, and always has had, a Vacuum Heating Pump. (In fact the original Nash unit is still there as a back-up!!!) I know because I (GS Dunham LLC) was involved in the sale and installation of the new unit. A vacuum pump is just a huge mechanical air vent that pumps the air out of the piping and creates a vacuum (depending on how tight the pipe is) in order to "stretch" the steam and help it move quicly and quietly through the system. Steam distribution is as much a function of Vacuum (air removal) as it is pressure in such large buildings. A vacuum also lowers the temperture of steam. So it is not truly accurate to say the building heats at 2PSI because without the Vacuum Pump the pressure would need to be higher to overcome the HUGE amount of pipe. Also remember that you either have a Vauum Pump OR air vents, not both. The vast majority of NYC Hi-risers have Vacuum Pumps.