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The Unseen Damage of A Flooded Steam System

There's more to a steam-heating system flood than meets the eye. In this episode, Dan Holohan troubleshoots a problem with an old one-pipe steam system. 


Episode Transcript

The couple had lived in the house for five years and loved it dearly for its Victorian charm. They'd been restoring it as a hobby and never would have considered parting with the old one-pipe steam system had it not started acting up.

"It bangs all the time now," he said. "It didn't used to, but it does now."

"It started all of a sudden," she agreed.

"Do the radiators heat well?" I asked.

"Not like they used to," he said.

"They heated much better before the banging started," she added.

"When did the banging start?" I asked.

"Right after the flood," he said without hesitation.

"What flood?" I asked. She looked at him and smiled the way only a wife can smile. He laughed and shook his head.

"The flood that I caused," he said. "You see, our boiler doesn't have an automatic water feeder. It never did. I feed it by hand about once a week." She continued giving him that smile. It said, You ain't easy to live with, but I love you just the same.

"Anyway," he continued, "I got a phone call so I set the valve on a trickle and went to answer it. The call was from my son. He'd had a car accident, nothing serious, but it was enough to make me jump in the car and go see. I forgot the valve was open, and by the time I got back, water was pouring out of the second-floor radiator vents."

"I was at work," she said, "The water ruined the ceilings we'd just finished restoring."

"And the next day, the banging started," he said. She nodded in agreement.

"When does it bang?" I asked.

"All the time," they said in unison.

I had a feeling about this one right away because I could see the system filled with water in my mind's eye. Let me tell you a bit about it before I explain where the banging came from.

It was a one-pipe steam system with a gravity return. The house was built in 1914 and while the boiler had been replaced once, the piping was all original.

There was a 2-1/2" main that ran from the boiler header across the center of the basement and down to the far end of the house. From there, two 2" mains broke left and right and followed the perimeter of the basement. Ten, good-sized, column-type radiators fed off the two mains. The total EDR on the radiators was 485 square feet. I knew that some Dead Man had taken great care with the pipe sizing in this house. The radiation load exceeded what a single 2" main in a one-pipe system should handle at low pressure (which is 386 sq. ft. EDR), so he split the load and used that 2-1/2" main up the middle of the house.

Half the radiators were on the first floor and the other half were on the second floor. The Dead Man had used the right size runouts to the upstairs radiators. He'd increased the horizontal runout to each riser by one pipe size to accommodate the steam and the condensate in counterflow. All in all, the system looked pretty good. The worn asbestos insulation bothered me a bit, but the home owners were planning to get rid of it soon.

We fired the boiler, waited ten minutes and sure enough, the system started to complain. The banging was everywhere at first, and then it moved to the ends of the mains after the system had been on for a while.

We went upstairs and checked out the radiators. They heated only about half-way across. The vents panted, and many of them squirted water. I checked the pressuretrol and found someone had set it to cut in at 2 psi and out at 6 psi.

"Who set the pressure this high?" I asked.

"The guy from the oil company," the man said. "He told us we needed the high pressure to push the heat into the radiators."

"What do you think of his idea?" I asked. He shrugged his shoulders. "The guy said it would probably take some time, and then he left. I haven't seen him since."

I cranked the pressuretrol down to where it belonged - cut in at 1/2 psi with a 1 psi differential. I would have set it lower if I could have, but this particular pressuretrol didn't go any lower than that. I knew we didn't need pressure to push the steam into the radiator. The steam wasn't getting that far. Something was stopping it.

Here's what I want you to see in your mind's eye. This job has 55 feet of 2-1/2" steel pipe, 138 feet of 2" steel pipe and 60 feet of 1-1/4" steel pipe. The total weight of all that pipe is about 960 pounds.

The Dead Man who designed the system supported those pipes with pipe hangers. He knew his pipes would contain steam and air, which weighs practically nothing, and condensate, which is heavier than steam and air, but considering the quantity, doesn't weigh that much either.

The Dead Man figured his pipes would have to handle about 121 pounds of condensate every hour. At any given minute, there would be about a quart of water (which weighs about two pounds) up in the pipes.

Now think about what would happen if you flooded this system. When you include the radiators, this system can hold 105 gallons of water. You know how much 105 gallons of water weighs? About 875 pounds! That's nearly as much as the all the pipe in the house.

How do you think the Dead Man's pipe hangers felt about carrying that much extra water weight? You think his mains sagged a bit under the strain?

It was hard to see because of the asbestos insulation, but those mains had sagged quite a bit and that's what was causing the water hammer on start-up. Steam mains are supposed to pitch a minimum of 1" for each 20 feet of run when the steam and the condensate flow in the same direction. The slight pitch allows the water to drain after each cycle. If the water lays in the mains between cycles, the steam will pick it up on the next cycle and drive it down the line where it will smash into the first available elbow.

So the extra weight did some unnoticed damage here, but that wasn't all that happened. Think about an old cast-iron, column radiator. The inlet is a bit higher than the bottom of the radiator, right? Old-time radiator manufacturers did that for a reason. Since a steam system is an open system, radiator manufacturers knew there would be a lot of corrosion taking place as the years went by. They deliberately left some space at the bottom of the radiator for the dirt and corrosion to accumulate.

When he flooded his system, the homeowner freed almost 80 years worth of crud from his radiators. It fell down the risers and gathered in the horizontal runouts between the main and the risers. Once there, it did a fine job of blocking the condensate from flowing back to the wet return. A puddle of water collected in each runout and the steam condensed in it before it had a chance to flow up to the radiators. That's why the radiators wouldn't heat all the way across. That's why the air vents were panting. The steam pushed and condensed, pushed and condensed. Raising the steam pressure only made a bad situation worse.

Some of the evil soup from the radiators also worked its way down into the wet return. That caused condensate to back up into the steam main and created a water hammer during mid-cycle. Can you see this all happening in your mind's eye?

The only way we could fix this one was to flush the crud out of the system. We disconnected each radiator, one at a time, and hooked up a hose to each. We broke into the wet return back at the boiler and flushed the system from top to bottom under street pressure. You should have seen what came out. There was stuff in there that looked like it was leftover from the birth of the universe.

Once everything was hooked up again, we corrected the pitch, making sure the mains sloped downhill at least 1/2" for each 20 feet of run. All of this was done after the asbestos had been abated, of course. When we were done, the homeowner reinsulated the pipes and we started it up.

The banging and clanging had left, flushed out with 80 years of crud that never should have been disturbed in the first place.

See? There's more to a system flood than meets the eye. So use your mind's eye!

Well, I hope you enjoyed that tale. And if you did, please share it with your friends. And if you haven’t already, please subscribe to this podcast. I have many more Dead Men Tales to share with you, and I appreciate your taking the time to listen. Without you, I’m just talking to myself! Thanks.

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