Hammer from Hell in Asheville, N.C.

Chris Campbell

My wife and I live in a 1941 home with a two-pipe steam system. The house has a bedroom addition from the 1980s. Each year over the past 3 our steam hammer problem in the bedroom grows worse. This year the pitch on the pipes was checked, cleaner has been added to the boiler, and the traps have been replaced with air vents. Nothing helps. The hammer is worse at start-up and you can hear "flowing water" in the pipes and covectors! Could the boiler be pushing water up the return into the bedroom which is on the first floor and very near the boiler in the basement?

Any thoughts and/or a professional in North Carolina / East Tennessee would be greatly appreciated.

gerry gill

can you post a picture

of what was done to the radiators? also a picture of the boiler piping and the type of pressure control device..also is there a name anywhere? like for instance mouat, brommel, wiley, hoffman, trane, etc....sounds originally like a sag in a pipe or a pipe without insulation but after the radiators were altered who knows now...

kevin coppinger_4

well I am certainly...

no two pipe expert but if its 2 pipe you should have no air vents on the rads....replace the traps...kpc

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Steamhead

That's probably a Vapor system

almost all 2-pipe residential steam installed in that period was Vapor. The term "Vapor" generally described a two-pipe steam system that ran at a maximum of 8 ounces of steam pressure or thereabouts. These systems were works of pure genius, and they were considered the Cadillac of heating in the first part of the 20th century. Unfortunately, hot-water finally eclipsed steam after World War II.

In 2-pipe Vapor, the radiators do not have their own air vents. Air is discharged along with condensate into a dry (overhead) return line. Air is then vented from the dry return at a central location in the basement, and condensate is returned to the boiler.

There has to be a way of keeping steam out of the dry return. This is why your system has traps. These contain thermostatic elements that will let air and water through, but close when steam reaches them. If steam gets into the dry return, some radiators will not heat since the pressure in the steam main and the dry return will be the same. Without a pressure difference, even if it's only a couple of ounces, the steam will not flow.

Traps were commonly used, but other Vapor systems used water seals or check valves on the return connections, or orifices on the supply valves to keep steam from reaching the dry return.

If the air can't get out, the steam can't get in. I've looked at jobs where the boiler was replaced and the dry return vent was removed, and the system then won't heat, and no one can figure out why. I recall a Trane Orifice Vapor job that was missing the dry return vent, and someone added vents to the convectors like they did to yours, and the system banged and hissed. Didn't take long to straighten that one out! The owner was so pleased he had us heat an addition by adding radiaton to his Vapor system.

Two things to do: First, take some pictures of a couple of radiators that still have the original equipment on them, and see if you can find any names on any of the hardware (valves, traps etc). Also take some pics of the piping around the boiler including any odd-looking devices you may find there. Post the pictures here. This will help us identify your system.

Second, if you haven't already, get a copy of Dan's book "The Lost Art of Steam Heating", available on the Books and More page of this site. Chapter 15 is devoted to Vapor and Vacuum systems, and the whole book is a very good read.

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