Published: June 24, 2014 - by Dan Holohan

Categories: Steam

two pipe air vent system

The building was on Fifth Avenue in midtown-Manhattan, and that’s one of the reasons why this one has stayed with me for so long. It was so stately and classy. It stood there with all the modern skyscrapers, looking very much like an aristocratic old man at a gathering of newly rich, Wall Street yuppies.

I was with a guy who had gotten his professional engineering license around the time I was born. He had brought me along for a couple of reasons. First, he thought I'd find the place interesting, which I did. Second, because he wasn't positive about what to do to fix the problem the tenant was having. And third, he knew that I have this library of engineering books that reach back to a time when central heating was brand-new. Comes in handy.

He told me that the tenant no longer trusted the engineering firm they had hired to write the specs for the renovation of the offices they occupied. None of their radiators would get hot. They used to get hot, but they didn't anymore. That was the problem. They hired this engineer because he was older than most of the people in New York City. They figured he'd know more about this stuff than most, which he did.

The project occupied just two floors of the grand old 15-story building. The tenant bought the space in this building, had it gutted, and then set out to make it look modern. The steam system that heated their two floors (along with the rest of the building) however, dated to Ragtime. Folks who buy space in steam-heated buildings often think that if they modernize their space the old heating system will watch, and nod, and also become modern. The new folks change the radiators, hide the pipes, and wonder why, with all the money they've spent, things aren’t going their way. This shouldn't be happening to them, but it is, and the reason why is because the rest of the building didn’t go along with their modernization.

In this case, the new tenant – these folks who had bought just two of the 15 floors – tried to fiddle the old system into the 21st Century. The consulting engineer, eager to please his client, decided to modernize just the portion that concerned the tenant by replacing the old cast-iron radiators with sleek, European-style, panel radiators made of steel, with very narrow internal passages (never a great idea with steam). The consultant also added thermostatic radiator traps, and thermostatic radiator valves to each radiator. He explained to his client that these modern additions would give them total control over the heat, but when autumn arrived, the only available heat came from the computers.

So one guy pointed a finger at another guy, who pointed at a third guy, who looked around for a fourth guy, who pointed back at the first guy. And you know the rest of that story. Which is why the oldest engineer in the City of New York and I were there that day.

Which brings me to the elephant. There were these blind men who come upon an elephant for the first time. One blind man touches the elephant's leg and tells the others that an elephant is like a tree trunk. But another blind man touches the elephant's tail and decides that the first blind man is an idiot. An elephant doesn't look like a tree trunk; it looks like a snake. And then up steps the other blind guys. They each grab a different part of the elephant, and each comes up with his own conclusion as to the true appearance of an elephant. None of them take the time to explore the whole elephant, and that's what’s causing the confusion and the disagreement.

The consulting engineer on this project decided to touch just two stories of this old elephant of a building. He saw antique radiators without steam traps, and declared that they must add traps because all steam systems of the two-pipe variety require steam traps (which isn't true). I imagine the consulting engineer also decided that the long-dead design engineer was a know-nothing fool. Who would design a two-pipe steam system without steam traps? Indeed!

The thing that should have nagged at the consulting engineer, though, was that this wonderful old building had heated splendidly for more than 100 years. And it did that without benefit of steam traps at the radiators. It's hard to argue with success, but the consulting engineer didn't consider that.

So the oldest engineer in the State of New York and I walked upstairs and took a look at the heating system in the neighbor's space. This is what used to be in the new tenant's space. One look was all it took to tell us what we had here. The tip-off was the size of the supply and return risers. On most two-pipe steam systems, you'll find big supply risers (because low-pressure steam is big), and small return risers (because condensate is small). There might be, say, a 1-1/4-inch supply and a half-inch return. Here, we had a 1-1/2-inch supply and a 1-1/4-inch return at each radiator. There was also a one-pipe-steam air vent on the return side of each of the original radiators. There were no air vents on the modern, steel-panel radiators, of course. They had thermostatic radiator traps and thermostatic radiator valves. Modern stuff. None of it worked, but it looked marvelous.

The oldest engineer in the United States of America smiled at me and I smiled back. We knew that what we had here was a two-pipe, air-vent system. That's why the new tenants with their newly modernized portion of the system had no heat.

There was a time in American Heating History when they didn't use thermostatic radiator traps. They didn’t use these devices because no one had yet thought to invent them. You cannot install what has not been invented. This lack of traps, however, didn't stop the Dead Men from installing steam heat. They just put in these two-pipe, air-vent systems, which look remarkably like two-pipe, direct-return hot-water systems. The steam leaves the boiler and heads up into the building. It favors the supply lines, of course, because these are usually larger than the return lines by at least one size. Steam follows the path of least resistance. The Dead Men put an angle valve on each side of every radiator so that tenants could shut off the heat if it got too warm. The air left the radiators through the one-pipe-steam air vents. The steam heated the radiators, and the condensate dribbled down the return lines. The steam flowed into the return lines along with the condensate because there was nothing there to stop it. After a while, there was steam everywhere, and that was perfectly normal for this system. And since there were so few moving parts, these systems lasted for as long as the building stood.

But then the consulting engineer came along and decided that he could put a party hat on the elephant, while leaving the rest of its body naked. He added the traps to a system that’s not supposed to have traps because there’s supposed to be steam in the returns (the new thermostatic radiator traps shut, and stayed shut). He got rid of the air vents on the radiators (even though they were supposed to be there), so the air had no way out of the system. And he added thermostatic radiator valves, which then stayed opened because the rooms were as cold as cold be. Steam couldn't enter the radiators because air couldn't leave. And if steam did enter the radiators, the condensate would have no way of leaving because the steam in the return kept the traps closed.

The oldest engineer in the Western Hemisphere and I told the tenant that they were either going to have to return to the 19th Century, as far as their heating system was concerned, or convince the rest of the tenants in the building to move boldly along with them (and at great expense) into the 21st Century.

And this being New York City, I'll leave you to imagine what the other tenants had to say about that.