wetviking
02-21-2009, 05:39 PM
Can anyone explain gas line physics… I'm installing a gas heater this spring and came across something peculiar, the 1" main enters the house and gets reduced to .5" prior to the meter and exits the meter as .5", then is connected to .75" pipe which eventually turns into what looks like 1.5" which runs to my furnace and water heater and is T'd off to .5" lines for each appliance. Question is, if my gas line is reduced to .5" at the meter, why do they use larger pipe down the line? I would assume this is for the same reason that the heater installation instructions tell you to use .5" for runs up to 25 feet and .75" for runs up to 100 feet. Anyone know? I'd call my local gas Co. but trust me, the people answering the phones do not have a clue.
Kind regards,
Wetviking
Poconos
02-22-2009, 12:23 AM
Gasses have mass and behave like any fluid. The larger pipe reduces the velocity which reduces losses around bends and cuts frictional loses due to contact with the inside of the pipe and additional turbulence. I forget but I think air drag increases as roughly the 4th power of velocity but it may be the 3rd power. I'm surprised they reduce the pipe diameter that much at the meter even if it is a short run. After the pressure regulator, located somewhere before the meter, the high distribution pressure is reduced to something in the 'inches of water' range. 5" sticks in my mind and I used to know that too. Long long time ago. When I lived in a house with gas service I do remember the high pressure was around 60 psi from the street thus they could use a small diameter plastic pipe for the runs before the pressure regulator.
Hope this answers your question.
Al