Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Hoffman Differential

byeckley Member Posts: 2
I am looking at a steam boiler replacement that has a Hoffman Differential Return trap(loop?). It has rust bubbles on it and worries me. If I remove this can I use a simple Hartford loop? I have about 40" from the end of the return to the water line on the boiler.


  • Steamhead
    Steamhead Member Posts: 16,734
    A Differential Loop does something entirely different from a Hartford Loop. It keeps the pressure difference between the steam and return side of the system from exceeding a certain amount, usually 10 ounces, thereby ensuring the water can return to the boiler by gravity.

    Nowadays we can control the boiler pressure with a Vaporstat. Set the Vaporstat to cut out at 8 ounces and you should be fine.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    ethicalpaulMad Dog_2
  • Jamie Hall
    Jamie Hall Member Posts: 22,947
    Well, you can. As @Steamhead says, make sure that your vapourstat is set to cut out at 8 ounces or less, and is reliable.

    You will need to reconfigure some of the piping. The dry return connection to the loop needs to be connected to the dry return outlet of the loop, and the steam line from the boiler to the loop needs to be removed and capped at the boiler header. The main vents above the loop on the dry returns can stay where they are.

    All that said... why bother? There are no moving parts involved. The castings and piping are heavy, and a few rust bubbles on the outside of 100 year old cast iron are nothing to worry about. If you don't mess with it, it will still be there, doing its job, 100 years from now.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Mad Dog_2shakingthrough
  • clammy
    clammy Member Posts: 3,094
    What is the water line on the boiler that is installed in comparison to what you are going to install ? If there’s a big difference I think I would walk around and be sure your new possibly lower water line won’t leave you w loose of water seals . Also take a look about and see if you have crossover trap . I would highly recommend a vaporstat and check your edr ,does the systems have traps or a water seal and what type of supply valves ,if there’s original and graduated orificed type valves then make sure you do not over size the boiler . If there is a loose of water seals then plan ahead and install a false water line to resolve the issue . Either way be sure to over size your header to ensure your your getting dry steam this would be beneficial to proper operation and performance of all steam system but 2 pipe vapor system will always operate well when supplied w dry steam . Poorly pipe boilers on 2 pipe vapor system gives them a bad name and the issues which will only be corrected by showing some respect by piping it above the manufactures min piping diagrams being there diagrams are all min .
    Peace and good luck
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    Mad Dog_2