Modern Steam Heating
Like Putting Rollerblades® on an Elephant
The building was on Fifth Avenue, right there in midtown-Manhattan, and that’s one of the reasons why this one has stayed with me for so long. The structure was so old and stately. It stood there among modern skyscrapers, looking very much like an aristocratic old man at a gathering of the newly rich.
I was with a guy who had gotten his professional engineering license around the same time I was born. He had brought me along for several reasons. First, he thought I’d find the place interesting. Second, because he wasn’t positive about what to do to remedy the problem. Third, he knew that I have this library of engineering books that reach back to a time when engineers used to have to know how to ventilate slave ships.
He told me that the tenant no longer trusted the engineering firm they had hired to write the specs for the renovation. None of their radiators would get hot. They used to get hot, but they didn’t anymore. That was the problem. They hired my friend the engineer because he was older than most of the people in New York City. They figured he’d know more about this stuff, which he did.
The project occupied just two floors of the stately 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, was as old as Cornelius Vanderbilt. Modern steam heating (such as it is) is often this way. The tenant thinks modern. The space now looks modern. The steam system, the engineer figures, is now also modern because of the stuff he had added. But, sadly, it’s not.
You see the trouble is that the rest of the building didn’t go along with the modernization. The new tenant––these folks who bought just two of the 15 floors––tried to fiddle the old system into the 21st Century. The consulting engineer, eager to please the client, decided to modernize just the portion that concerned him by replacing the old cast-iron radiators with sleek, European-style, panel radiators made of steel (which, with their narrow passages, is always a mistake with steam). The consultant also added thermostatic radiator traps (which had not been there before), and thermostatic radiator valves (to give the client “total control over the heat”). And when autumn arrived the only available heat came from the modern computers.
So this guy pointed the finger at that 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.
Now, have you ever heard that parable about the blind men and the elephant? It goes like this. One blind man touches the elephant’s leg and declares that an elephant looks like a tree trunk. Then a second blind man touches the elephant’s tail and decides that the first blind man is an idiot. An elephant looks like a snake, not a tree trunk. Bring in the other blind guys, have them grab other parts of the beast, and each comes up with a different conclusion as to the true appearance of an elephant. None of the blind guys take the time to grab the whole elephant and that’s the crux of the problem. (Why the elephant stood still for all of this touching has always been a mystery to me.)
The consulting engineer on this project decided to touch just two stories of this white elephant of a building. He saw old radiators, sans steam traps, and declared that these devices must be added because all steam systems of the two-pipe variety required steam traps. And I also imagine the consulting engineer declared the long-dead design engineer to be a know-nothing fool. “What sort of cretin,” he would say, “designs a two-pipe steam system without steam traps? Indeed!”
The thing that should have nagged at the consulting engineer, however, was that the building had heated just fine for a hundred years. This is one of the things we really need to consider whilst modernizing (such as we can) steam heat.
So the oldest engineer in the State of New York and I walked upstairs and took a look at what used to be the heating system in the new tenant’s place. One look was all it took. We both knew 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 steam is BIG) and small return risers (because condensate is small). There might be, say, a 1-1/4-inch supply and a 1/2-inch return. Here, we had a 1-1/2-inch supply and a 1-1/4-inch return to each radiator, and that was the tip-off. 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 traps and TRVs. Modern stuff. Didn’t work, but 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 the modern (such as it was) portion of the system had no heat. You see, there was a time in American Heating History when they didn’t use thermostatic radiator traps. They didn’t use them because these devices had not yet been invented. You cannot install what has not been invented (an important design consideration). This lack of traps, however, didn’t stop them from installing steam heat. They just put in these wacky systems that 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 they are usually 1-1/2 inches (which is larger than 1-1/4 inches). They put an angle valve on each side of the radiator so that you could shut off the heat (the Homo Sapiens control valve––quite modern back then!). The air would leave the radiators through the one-pipe-steam air vents. The steam would heat the radiators, and the condensate would dribble down the return lines. The steam would flow 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 then-modern system. And since there were so few moving parts, these things lasted for a very long time.
But then the consulting engineer came along and decided that he could put Rollerblades® on the elephant’s feet without affecting the rest of the elephant. 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 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. And he added thermostatic radiator valves (which stayed opened because the rooms were as cold as Pluto).
And that’s they called modern steam heat (such as it is).
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, or convince the rest of the tenants in the building to move boldly along with them (and at great expense) into the 21st Century.
This being New York City, I’ll leave it to your imagination as to what the other tenants had to say about that.
Which brings me to the first piece of advice I’d like to offer you as you strive to bring old American buildings into the new millennium.
If you’re not sure what you’re looking at, put your hands in your pockets. Get out there and grab the whole elephant! Give him a squeeze. See the entire system, not just your client’s portion of it. Wander around and knock on doors. Find the building superintendent and drink coffee with him. Have him tell you all about the peculiarities of the place. Get a sense of the whole building because the whole will most certainly affect your portion of it.
Don’t remove stuff that you don’t understand. That old cast-iron thing that’s hanging from the boiler room ceiling is not some heating tonsil or adenoid that no longer serves a purpose. It’s there for a reason. If you don’t know what it is, find out. There were at least three dozen companies making vapor equipment in the early 1900s. Their goal was to make future generations scratch their heads in wonder. Much of this stuff is still there, and most of it makes the system work. If you don’t know what it is, smile a silly smile, and tell your client you’ll get back to him. Then visit us on the Internet at www.HeatingHelp.com. If it’s old and weird, you’ll find it there. Look around for missing parts. Someone might have gotten to the job before you did. They may have ripped out some important stuff. You can often tell what’s missing by looking at what’s left. For instance, if you’re in the basement and you see radiators hanging from the ceiling, that means that the job once ran on gravity return––even if the job now had a condensate pump or boiler-feed pump. If you see dry returns going into the chimney, you know that they once used the draft to induce vacuum in the pipes. Knowing what used to be there can help you figure out what’s wrong now.
As You Modernize, Know that the Air has to be Able to Get Out
There has never been a steam-heating system that didn’t need to be vented in one way or another. Sometimes you can see the air vents. They’re right there on the radiators or at the ends of the steam mains and dry return mains. But other times, the “vents” aren’t quite as obvious. The “vent” may be a condensate receiver. And if the steam traps have failed, someone may have plugged that vent on the receiver. If the air can’t get out, the steam can’t get in.
If the system is old, take a walk down to the ends of the steam mains and look for 1/2-inch lines that cross from the end of the steam main to the end of the dry return main. These lines will be higher than the steam and return mains, and there will be a thermostatic radiator trap in them. That’s your “air vent.” The steam pushes the air to the end of the main. The air passes through the 1/2-inch line (and the thermostatic trap) and enters the dry return main. Somewhere beyond that, the air leaves the system through a main vent that’s probably as big as a muffler on a minivan.
Wander around and find these strange pipes and huge vents. And know that if that 1/2-inch crossover thermostatic trap has failed, the steam will get into the return line and shut the big air vent before all the air has a chance to get out of the risers. You can start your modernization project (such as it is) by replacing that little crossover trap.
If your system has a vacuum pump, that pump becomes your “air vent.” It will come on with the burner and pull all the air out of the system. And once a system is sized for vacuum, it’s never going to work well without the vacuum pump.
My point being, a vent doesn’t always look like a vent. But it’s there. Somewhere. Know that something has to stop the steam at the terminal units.
That is, with the exception of that wacky two-pipe, air-vent system. You will know that one by its big pipes (on both supply and return), and those two angle valves at each radiator. Beyond this oddball, every steam system should have something at the terminal unit to keep the steam from moving into the dry return lines.
Usually it’s a trap. If you’re looking at a fan-coil unit, it will probably be a float & thermostatic trap. It could even be a bucket trap, if the load is relatively constant. As you modernize, make sure every trap in that building is working. One bad trap can disturb the operation of an entire system. Check them. Thermostatic radiator traps will show a measurable temperature drop from inlet to outlet. These, you can check with a thermometer. F&Ts, and bucket traps, release condensate at saturated steam temperature, so you’re wasting you’re time with that thermometer when you’re dealing with these. Check them by opening a valve or a union at the trap’s outlet and take a look at what comes out. You should see hot condensate and some flash steam when the trap is working.
If you don’t see a trap at that terminal unit, look for an orifice at the inlet or the outlet. The orifice will probably allow in about 80% of the unit’s rating. If the system pressure is too high, too much steam might push through the orifice and enter the return lines. When in doubt, crank the pressure down.
If you’re out at the ends of the steam mains and you’re not seeing traps, don’t be surprised. They didn’t use traps on steam mains that dropped into the wet return (on gravity return systems). You might see a U-tube arrangement if the end of the main connects to a dry return. That U-tube is your “steam trap.” If you raise the pressure too high, you’ll blow the water seal out of the U-tube and the system will heat unevenly. When in doubt, crank it down. Remember, with steam heating, the required system pressure is a function of load and pipe size, not the building size. And if you see those U-tubes at the ends of the mains, they’ll probably have those crossover air-vent/thermostatic traps as well. Look around for them, and fix them, if necessary.
Be Aware of Boilers on Pedestals
You’re walking through the basement and you see this boiler up on a concrete altar. This is not evidence of some ancient religion (oh, what will the archeologists of the future think of us!) That boiler is up there for a reason. This system has a gravity return and the boiler’s water line, in its present elevated state, is covering the wet returns that dip under doorways. If you’re replacing that boiler, you’re liable to wind up with steam in those wet returns if you lower the boiler to the floor, or if you add a condensate- or boiler-feed pump to the system.
As you face this challenge, know that you can easily solve it by constructing what’s known as a “false water line.” This is a piping arrangement that lets you lower the boiler (or add a boiler-feed pump) without disturbing the integrity of the old system. You can read about false water lines in my book, “The Lost Art of Steam Heating” (available at www.HeatingHelp.com), should the need to know ever arise.
Modernizing (such as it is)
As you modernize, know that they often mixed one-pipe radiators with two-pipe radiators.
They did it all the time, and thought nothing of it. Don’t let the integration of the systems rattle you. Generally, the two-pipe radiators leave the main before the one-pipe radiators. That’s so the condensate from the one-pipe radiators won’t drain into the supply lines heading toward the two-pipe radiators, causing the steam in the main to condense. Be aware of this piping subtlety if you’re moving steam pipes around. So much of this is common sense, though. You just have to think like steam, air and condensate. If you were inside those pipes, what would you do?
Be Careful when Sizing Pipes
You’re a modern engineer so you’re probably used to sizing pipes for commercial steam systems. Maybe you just did a job with reheat coils that were taking steam from a high-pressure source. Or it could have been that sterilizer in the hospital that you specified not long ago. You reached for your ASHRAE books and turned to the Moody Friction Flow Charts and went to work sizing those pipes. You figured the load and the pressure drop and the velocity. Which is great for a commercial system. But please don’t use those charts if you’re modernizing a space-heating steam system. There are charts that are specifically put together for space heating. You can find them in the older editions of the ASHRAE and ASHVE books. You can also find them in my books, “The Lost Art of Steam Heating” and “The Golden Rules of Hydronic Heating.” The difference in the charts is that, when sizing for space heating, you’re working with pressure drops that are measured in ounces, not pounds. Steam distribution, in space-heating systems, is mostly about the pipe sizing. Use the right charts and you’ll be a much happier person.
Write into your specs that the contractor must thoroughly clean the system when the work is done. And I’m not just talking about just the boiler. Have the contractor get hold of some trisodium phosphate (use one pound of TSP per 50 gallons of boiler water) and let him run it through the system with the steam. Have him waste all the condensate that returns from the system and make him keep doing this until all that goop from the past 100 years has left the system. The natural state of a steam system is to corrode, so you’ll be doing your client a good service by overseeing the cleaning of the system. Most contractors will try to avoid having to do this, and that’s why you should write it into your spec.
What's in It for Your Client?
If you’re specifying a new boiler, and if that boiler is sized to the connected load, and if the system is piped well and thoroughly cleaned, and if the air can get out on every firing cycle, your client is going to save money on fuel. That’s good, right?
The modernized system will also be better balanced. That’s because you were very aware of the piping arrangement, the size of that piping, and the way the air was leaving the system. And when you were looking at those old steam traps, you were also thinking of them as “air vents” because they pass the air to a place where it can leave the system. You also thought of those traps as “balance valves” because they keep the hot side hot and the cold side cold.
Most important, your client is going to be more comfortable with the modernized system, and isn’t that what they’re really looking for you to deliver––comfort and improved efficiency? You’re going to give them an updated steam-heating system that doesn’t make noise, doesn’t use more fuel than it should, and allows them the luxury of keeping the windows closed in February––perhaps for the first time in decades.
Good for them, and good for you!
Finally, What's in It for You?
When you take some old American steam-heating system and modernize it, you get a special kind of satisfaction. It comes from knowing that you were able to understand the mechanical engineering that came along before you did. You were able to use your education, your research capabilities and your design skills to bring that old system back to its fullest potential.
Remember, it is not always possible to rip out the old and begin anew. Consider that wonderful old building on New York’s Fifth Avenue. We had to take it back 100 years or so to make it work again. Who knows, maybe next time, you’ll be the one who will know exactly what to do.
And won’t that be wonderful!