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Steam Slow to Reach 15th Floor Along One Riser
In my 16 story/80 unit building in lower Manhattan, we have a two pipe steam system. All new (200 plus) radiator steam traps. And all new F&Ts in and around basement/boiler room. System works really well now on .5psi. Except for one riser that is giving me trouble. Steam is taking too long to reach the upper floor radiators on this riser. Up to the 5th floor it's fine. At the 5th floor the building sets back where there is a terrace. So the riser which runs up that exterior wall is offset where the terrace is, then continues vertically to the 15th floor. Radiators on that riser above that offset are slow to heat up, especially at that low psi. Obviously this results in not a lot of heat time, thus complaints from residents. I noticed on another somewhat far flung riser, the 4" header just before the riser has a small air vent. I'm wondering if I can use air vents at my problem riser to help steam get up quicker. I have heard that a vent at the end of the header and somewhere toward the top of the riser can help steam move quicker up the run. Is this advisable with my two pipe system, and if so, what product should I be looking at? And what would be optimal placement/configuration? Header and riser are 4".
Also, though not along this particular riser, before our recent steam trap replacement job, I saw a couple radiators toward the top of the building that had two stacked steam traps at the same location, a top one being a larger trap acting basically as an air vent but handling no condensate. We removed these old configurations when we installed the new traps and have seen no ill effects in operation, but I'm wondering if I shouldn't try that configuration on a couple of radiators near the top of this problem riser. Or if I should just give air vents a try.
Any insights would be much appreciated. Thanks!