Rehabilitating a 1917 One-Pipe Steam System

May 12, 2000
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I received an unexpected phone call from the owner of a vintage townhouse built in 1917, which had had a fire on the upper floors two years ago. The owner wanted to put the heating system back into operation.

The five-story building is located in a historic district on the East Side of Manhattan. I was told that the original architect was Cass Gilbert, who also designed the New York City Public Library and the United States Customs House in lower Manhattan.

An addition was put on the rear in the 1950s, and I could roughly date the addition from the style of the radiators added to that section of the building.

The fire started on the third floor, and there was extensive fire and smoke damage above, with water damage to the entire structure. The building could be rehabilitated and put back to use. With the present booming economy, it was bound to find an eventual buyer.

The heating system was a one-pipe steam system, and I believe that the boiler was originally fired with hard coal. The original radiators and piping were still intact in the first through fifth floors, except where the radiators were disconnected in the process of the structural repairs to the building. Several radiators were missing.

The building addition in the 1950s necessitated changes to the heating system to heat the rear of the building. However, these changes were not made in a way to make the system function properly, and the lack of understanding of the functioning of a one-pipe steam system led to more problems.

A new boiler appeared to have been installed in the 1950s. It was an H.B. Smith boiler, Series 25, with a firing rate of no more than 6.45 gal of No. 2 fuel oil per hour. However, the burner was a Carlin 950 FRD-1 burner that is rated to fire between 7 and 13 gal of No. 2 fuel oil per hour.

I contacted the manufacturer’s rep for H.B. Smith, and he gave me the recommended firing rate for the boiler, as my H.B. Smith binder did not have the rating for this unit, which is now considered obsolete and is no longer manufactured. The particular boiler in the building was originally designed to be hand-fired or stoker-fired with hard coal. The company has since come out with a new series of boilers to take the place of the Series 25.

I could tell that the boiler was a replacement unit, since it had a steel shell with fiber glass insulation, and fiber glass insulation was not generally used to insulate boilers until the 1950s.

Changing the Burner

Another problem arose when I examined the Air Resources permit from the New York City Depart-ment of Environmental Protection (DEP). All fuel oil-burning equipment over a gross input of 350,000 Btuh must have a permit to operate within the city limits of New York. The permit was for a Carlin 301 CRD burner. Thus, the burner on the boiler did not match the permit and was illegal.

The owner of the building wanted to replace the boiler. I knew from experience that the cast iron boilers manufactured by H.B. Smith were reliable, and could last for decades without replacement. So what the plumber did — which he was not supposed to do — was to open up the doors on the front of the boiler.

When we looked inside, we found a considerable amount of soot, as the unit had not been cleaned in several years. We did not see any internal water leaks, so I pronounced the boiler in generally good condition.

But when the doors were put back on the boiler, the plumber did not have any furnace cement or roping to properly seal up the doors, so when the boiler was turned back on, smoke came out of the front of the boiler, and the smoke ended up on the third floor.

The boiler was quickly shut off. I told the owner that the burner needed replacement, as the present burner was not only illegal, but it had not been manufactured by Carlin for at least 25 years. I quickly called the Carlin rep, and was told that the Model 301 CRD burner that was on the permit was no longer being made, and the new model was a 301 CRD PA.

By phone, a representative at the DEP told me that putting on a 301 CRD PA burner would not require a new permit filing with the city. In the subsequent weeks, the owner replaced the burner.

Additional work along with the burner replacement included sealing up the doors, a boiler cleaning, and putting the barometric draft back into proper operation. I also told the owner to have the fuel oil lines purged of any sludge, and to have the fuel oil tank cleaned of sludge as well. I also recommended a chimney cleaning.

On The Steam Side

My initial survey of the building included a listing of every radiator, its location, and size, so I could go back to tables to compute the total square feet of equivalent direct radiation (EDR). But when I first did that, there was a major discrepancy between the total exposed radiation in the building and the boiler net output.

It turned out that the source of the smoke on the third floor was hot air ducting that ran from the basement to the third floor. There were cast iron radiators in the ductwork in the basement, and the radiators heated air that supplied the third floor. I told the owner that the ductwork needed to be cleaned out, as it looked like there was 80 years of dirt in the system. This dirt was a potential indoor air quality problem.

In those days, the fin tube steam coil did not exist, or else it wasn’t widely used. The cast iron radiators have the advantage of being fairly easy to clean in the ductwork; all you need to do is to brush them off, and you don’t need high-pressure water the way you do with fin tube coils today.

The steam piping was installed incorrectly when the new boiler was installed in the 1950s. The steam piping above the boiler and in the boiler room must be considered part of the boiler itself.

It is here that any condensate or water which is mixed with the steam is separated from the steam and returned to the boiler. Energy waste results when the steam sent into the steam lines has more than 2% condensate or water in it.

It is imperative that steam and condensate flow in the same direction in a steam line. There were two take-offs from the boiler into the header. For the right take-off, the condensate was flowing against the direction of the steam flow. That is bad, because it creates a fluctuating water line in the boiler. You will see it happen when the water in the sightglass bounces up and down. Other factors can cause this bouncing up and down to happen, including dirty water in the boiler.

Another problem is that the header was only 20 in. above the water line in the boiler. For low-pressure steam systems, one should have the main header at least 24 in. above the boiler water line.

The equalizer line from the main steam header back to the boiler was undersized, being only 1-in. dia, and there was a steam trap on it. Note that this building is heated by a one-pipe steam system. For a boiler firing at 3.5 gal of No. 2 fuel oil per hour, the equalizer should be 21¼2-in. dia.

Expansion and contraction must be allowed for in the main steam header, and to do this, you need to make offsets to allow for the expansion and contraction.

Returns Removed

When I inspected the system, I noted that large sections of the condensate return lines on the floor of the basement had been removed from the system. Also, I noted that every condensate return line had a steam trap on it, even though the system had one-pipe steam radiators.

By removing portions of the condensate return lines, what was once a wet return system was changed into a system with a dry return. When one does this, in conjunction with changing the water line in the boiler, one can upset rather dramatically the operation of the system.

To get the condensate back to the boiler, a condensate receiver and condensate pump were installed on the system, which were totally unnecessary. I also believe that several of the steam lines feeding the radiators in the new section of the building, put on in the 1950s, may be undersized, although the analysis had not yet been completed at the time of the preparation of this article.

I did find a steam trap on a line on an upper floor draining condensate out through a pipe piercing the wall; to do this, a steam trap was put on this “relief” pipe.

Some very strange things had been done to the system in the building. It is going to take tens of thousands of dollars to rectify the mistakes.

Before I finish this article, let me tell you a little secret. If you have a one-pipe steam system, try operating it with 0.5 lb of steam pressure. Almost every one-pipe steam system that has ever been built can operate on just that pressure. Crank the pressuretrol way down, and you will find that the system operates much quieter.

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