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Repair, Replace, Convert 1925 Steam system

My home has a two pipe steam system installed in about 1925. Based on what I have read in The Lost Art of Steam Heating, the system is two pipe steam with Hoffman steam traps on the return side of every radiator. The supply and return lines run parallel to each other around the top of the basement. There is a small Hoffman steam trap connecting the supply and return at the end right before they both dive to the floor where they are connected together and return to the boiler. The supply also has a connection about 1/3 of the way around the loop where it Ts and one branch dives to the floor to return to the boiler. The near boiler plumbing includes a Hoffman differential loop with a steam vent. This is the only vent I have been able to find. Also there is no expansion tank.

The boiler appears to be the original US Standard. Originally fired with coal it was converted to oil some time ago. The oil burner is probably inefficient based on its 30+ year age.

The system still heats well but is expensive to operate. After turning the pressuretrol down from 5# to 2# the banging has stopped and steam evenly distrubutes to the radiators. What is the best economic option if I plan to live in the house for 20 years? Repair the existing oil burner, steam traps, insulation etc. Replace the boiler with a new model but keep the system running on steam. Or, convert the system to hot water at the same time I replace the boiler. The radiators appear to be connected at the top with about 1/3 of them narrow column water type anyway. The supply to each radiator is 3/4", return 1/2". The main supply line appears to be a 4" line with the main return 1 1/2"

Any assistance would be helpful. My home is located between Omaha and Kansas City and not in an area with lots of knowledgable contractors.


  • A vaporstat; 0-1 PSI

    part number L 408A 1132 would control the system properly, and a properly sized, modern steam boiler would save some fuel. It looks to be quite intact, and serviceable. The contractor that does the work is the single most important factor in saving fuel.

  • Hoffman Differential Loop System

    Noel gave you a a good pressure control.

    I preffer the Honeywell L408A1157. It allows you to tinker with steam pressure settings up to 4 PSIG. This vapor stat also has a differential control that allows you to set the differential from 0-16 oz.

    Vapor systems are a funny creature. Many can give excellent heating at settings as low as 8" high pressure with a diffewrential of 2-4". which means that you would be able to heat the building with as low as 4' steam pressure.

    The differential setting is used based on the recovery of the steam pressure which is governed on how the burner operates.

    Some fuel burning equipment causes a slow rise in steam pressure. This is not a problem because you can set the differential control high of low depending on how fast the steam pressure is restored to the system.

    Example: The burner shuts down at 8" the setting is for a 4" differential. When steam pressure reaches 8" the burner shuts down.

    Steam pressure in the boiler drops to 4" and the burner comes on. The steam pressure continues to drop slowly. If the steam pressure drops below 3" there may not be enough sytyeam pressure in the system for steam to reach all the radiators. If that occurs you would need to set the differential to 3" that way the steam pressure would not drop to far below 4" steam pressure.

    Some older systems were designed to operate up to 2 PSIG. The 2 PSIG senario occurs when the outdoor temperature is around 20 degrees or less.

    Proper heating at times may require steam temperatures to be at 215 degrees. All of this is dependant on the amount and size of the radiators.

    In your home only you will be able to make the determination of the steam pressure.

    In old buildings I usually start at 1.5 PSIG and work downward. I continue tio lower the steam pressure until the house ca not maintain proper temperature. Once I find the bottom line I then can determine the proper operating temperature.

    Look at the boiler gauge. See if the gauge also reads in vaccum. If it only reads pressure replace it with a compound gauge. The gauge should read 30Hg-0-15.

    It appearts that the vent valve on the system is orignal. If it it is the system should go into vacuum. If your system is capable of producing vacuum and does not bang do not change any thing.

    If the vent valve is not a vacuum type buy a vent that can hold system vacuum.

    Some vapor systems that were converted from coal can operat as a vacum system. Other systems may bang when they operate in a vacuum.

    If you can operate in a vacuum with out banging you will save some fuel. The boier will produce steam below 212 degrees if the piping system is tight and can hold a vacuum.

    Vacuum will be produce when the burner shuts down and the steam in the system condenses. The higher the vacuunm the lower the steam temperature will be.

    Low steam temperatures on start up is good. Principaly because steam circulates at the lower temperature. it will begin to heat the pipe and radiators quicker than if the boiler had produce steam at 212 degrees.

    The temperature of the steam does not matter if the thermostat gets satisfied sooner.

    Idf money is no object and you are looking for long term economics you can replace the boiler. The newer boilers are smaller and steam faster. They steam faster becuse there is less water in the boiler to heat up. Additionally the internal design for heat transference in most new boiers is superior to the old boilers.

    If you replace the boiler with a new smaller boiler make sure that all the low return lines are emmersed in water.
    Additionally make sure that any return line that ties into the bottom return with a T connection has at 3" of water above the T connection.

    Additionall if there are check valves at the bottom of the differential loop or check valves are in the return befire ofr after the differential loop that they be replaced with new ones.

    Keep that old steam system. If you change it to hot water and if the job is done correctly you will save some fuel but you will not live to see the pay back.

    As to an expansion tank, steam system do not need them, do not let any one indstall one as you will waste your money and screw up the system.

  • Jake, I used that control, because

    ....because the Differential loop acts when the pressure gets above that range, and the zero to four PSI vaporstat isn't very sensetive below a pound.

    Been there....

  • Steamhead
    Steamhead Member Posts: 15,992
    Keep the steam

    One of the advantages of steam over hot-water is that most of the pipes drain dry when the system shuts down. That means they won't freeze during a power failure. The exceptions are the wet returns in the basement and the boiler itself. But water damage would be minimal where these pipes run.

    You can still get parts for your steam traps, and if the vent on the Differential Loop quits the best replacement is a Gorton #2.

    Nothing beats a new boiler for efficiency. But if it's not time for a new one, the existing boiler can often be upgraded.

    That's probably not the original boiler. It is a National-US, which was a company formed by the merger of National Radiator and U.S. Radiator in the 1950s. This company later became part of Slant/Fin. The Differential Loop you have was made in the 1920s.

    The boiler looks like it was an "all-fuel" design which meant it could burn coal, oil or gas. The flue passages inside the boiler are probably rather large- too large to extract all the heat available from oil or gas. However, it may be possible to strategically place bricks or baffles in the flue passages to slow down the hot flue gases so they give up more heat before leaving the boiler. This must be done by a knowledgeable pro. You'll be able to see the results when the stack temperature goes down.

    The photo doesn't show the oil burner itself. If the burner is an older type, upgrading to a "flame-retention" type will increase efficiency. Flame-retention burners make hotter fires, which often makes it possible to reduce the firing rate and still get the same amount of heat.

    Vapor systems were the Cadillac of heating in their day, and are still some of the best out there. With proper care, yours will last many more years.

    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Convert it to a new oil or gas power burner

    with a good contractor and a little refurbishing those boilers last forever. It looks like it is in pretty good shape.

    With some proper adjustments after a new burner and proper set up I have gotten combustion efficiencies on those boilers to 78 to 79%.
  • J. W. Trimmer
    J. W. Trimmer Member Posts: 9
    \"37\" series boiler

    The boiler is a National-US All fuels boiler "37" series. The plate says 900 sq ft of steam or 239,000 btu/hr on oil. The oil burner is a National oil burner 52AF-G-4436. Any suggestions for a replacement oil burner?
  • Steamhead
    Steamhead Member Posts: 15,992
    That sounds like the original burner

    Most new burners I see these days are Beckett, but I run across Carlin, Riello and Wayne burners too. Each brand has its proponents, but I don't think you can go wrong with any of the above. The most important thing is a proper installation!

    Talk to your oil company, they may have a brand they are used to working with. It can't hurt to go with what they handle.

    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
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