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Old 02-27-2010, 11:50 PM   #1
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Steam Heat Main Vent

My (old) house has a one-pipe steam heating system. The main vent is at very the end of the steam supply main, on a tee in line with the vertical pipe that starts the wet return. Everything I've read says that the main vent should be about 15 to 18 inches before (that is, upstream of) the end of the steam supply main, not at the end.
Ques.1: How am I hurting by leaving the vent where it is; why is 15 to 18 inches better than zero inches? What is gained by relocating the vent?
Ques.2: How big a job is it to tap into the 2-inch supply main?
Thank you for your answers.


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Old 02-28-2010, 04:59 AM   #2
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I have found this site to be most helpful for my steam heating questions


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Old 02-28-2010, 09:22 AM   #3
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Change your point of view. The system was installed at least 50 years ago, probably a lot longer actually. The guy that installed it new what he was doing. ( it came with the terratory back then) Unless someone has messed with the system, leave it alone. If you think you are having delivery issues....

Bad radiator vents
Bad main vents
Clogged or partially clogged return piping
Wrong pressuretrol setting
Always ask to see your contractors license!
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Old 02-28-2010, 09:43 AM   #4
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15 to 18" is because as the steam and water reach the end the water will basicly slam into the elbow. some water will go down and some up and into the vent causing vent damage. It will work at the end as it already has for years. But the proper location is before the end of the main.
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Old 02-28-2010, 02:45 PM   #5
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As John said, proper is at around 18" before the end of the main.

As NH said. its been like that for a long long time. No reason to change it now. Unless your replacing teh main vent every year or 2.
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