Dan Holohan: How one missing pipe can make all the difference
A friend of mine who is excellent when it comes to old steam systems, posted on www.HeatingHelp.com about a problem he was having on a job.
The problem wasn’t in the steam-heating part of the system, which took care of the second and third floors. It was in the hot-water zone that a long-gone contractor had piped off the steam boiler to heat the first floor of the house.
The previous owner of the house had contracted for that part of the job and it had been a problem ever since the new owners moved in. My friend said the homeowner told him the banging was sometimes horrendous, but it was as quiet as a tomb when my friend visited the job. Life’s funny that way.
And my friend, being an excellent steam man, posted photos and a sketch of the steam part of the job. There were some flaws in the system piping, but none that would cause all that banging on the first floor.
I thought about this for a while, how he went right to the steam part of the system. Most of us tend to go to the places where we’re most comfortable when troubleshooting. If we know steam inside and out, we’re going to look at the steam side of things, even though the problem is on the hot-water side. That’s human nature and we always should be a bit wary of human nature when we’re searching for solutions.
All the steam-savvy contractors that post on www.HeatingHelp.com were commenting on this steam pipe and that steam pipe and how it could be made better. That’s what they were good at.
I was looking at the piping for the hot-water zone. I’m a steam guy, too, but I’m also a born-and-raised New Yorker, so I know what a Brooklyn Special is and that’s what I was looking at.
Well, sort of.
The Brooklyn special
Years ago, when I was getting my hydronics education, mainly from old books and old men, I heard a contactor use that Brooklyn Special term at a trade show. He was talking to a boiler rep at the time and asking about certain below-the-waterline tappings on their steam boilers. He told the rep he never worried about not having enough work because according to the U.S. Census, there were a half-million one-pipe steam-heated homes in Brooklyn, New York alone. Imagine that.
A Brooklyn Special was how they heated the basements of many of those homes with hot water instead of steam. Steam boilers go in the basement, of course, and steam-heated homes traditionally didn’t have heated basements unless the homeowners were wealthy. And in that case, the radiators wound up either on the basement ceiling or high up on the basement walls. In either case, that’s to get those radiators above the boiler’s waterline.
But most of the folks who came to own those old houses a bunch of generations further down the line didn’t like the look of ceiling-mounted radiators. And having a cast-iron radiator hanging on the wall like a picture of the family wasn’t very decorative.
So once copper-fintube baseboard became available in the 1950s, the New York City contractors tapped into the water in the steam boiler at a point below the boiler’s waterline and ran a loop around the basement. They used a circulator and two flow-control valves, one on the supply side to the baseboard and the other on the return side. This prevented overheating when the pump was off. They wired the pump to a thermostat and used a strap-on aquastat to sense the temperature of the boiler water flowing out to the hotwater zone. It’s simple and it works like a charm.
And since they were successful with this, they started doing the same thing on the upper floors. This works as long as you don’t have any air vents up there. It works for the same reason water stays in a straw if you hold your finger over the top of the straw and lift it out of a glass of water. It’s gravity vs. atmospheric pressure, and you can run a zone like this up to the third floor as long as you fill it with a purge hose and make absolutely sure air can’t get in from the top.
John Rogers, a guy I worked with when I was at the rep years ago, was old enough to be my grandpa. He had never gone beyond high school but just before he retired he sat for the New Jersey Professional Engineer license and passed on his first try. He did that just for the heck of it. Smart fella.
He’s the guy who told me about the bypass pipe and how you absolutely had to have it if you were going to do a Brooklyn Special above the boiler’s waterline. The bypass would take water that’s been through the hot-water zone and blend it on the suction side of the pump with the real hot water that’s coming out of the boiler. You use two globe valves to balance the flow between the boiler water and the returning water. You check the supply temperature with a thermometer while the boiler is making steam and you make sure it’s not hotter than 180° F at the pump’s discharge.
“That’s to keep the water in the zone from flashing to steam when the pump shuts off,” John explained to me way back when. “If you put water that’s 215° up there above the boiler waterline the pump will keep it in its liquid state by adding pressure to the water. But when the pump shuts off on the thermostat, the hot water will turn to steam and just sit there.
“It won’t shove the water out of the zone because the air can’t get into the zone. The next time the circulator starts, the steam will collapse and you’ll get severe water hammer. So always remember to have that short bit of bypass piping down there between the returning water from the hot-water zone and the hot supply from the boiler.”
And there you go. One missing pipe can make all the difference.
I posted on the www.HeatingHelp.com thread about this and the steam guys turned from looking at the steam pipes and considered what I was saying. They began to see it in their mind’s eye and I hope the same is happening for you right now because this is a common problem in areas where contractors add hot-water zones to steam boilers without using a separate heat exchanger or the boiler’s tankless coil to separate the steam part of the system from the hot-water part of the system.
I learned this from one of the smartest heating guys I’ve ever known. I’m not that bright. I could never pass that P.E. exam like John Rogers did. I just had the good sense to shut up and listen when he was trying to teach me something.