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Honeywell Heat Generator #1

Hi Dave,

Yes! It originally had mercury in it and probably still does. Read about its function in the system in the Library section of this site, listed under Old Hot Water.

Best regards, Pat


  • Bubblehead
    Bubblehead Member Posts: 2

    I was just at a job to help with a boiler replacement of a turn of the the century house, last century that is. It has
    an old coal fired boiler converted to gas. Piped on one of
    the returns is a Honeywell Heat Generator #1. I believe
    this contains mercury, Anyone know if this is correct.
    And what the heck is it. The expansion tank in the attic is
    piped to the top of it. I will replace with diaphragm type.
    Any thoughts.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Please do not replace the open expansion tank OTHER THAN IN KIND unless you also remove the Heat Generator and convert the system to forced circulation!

    Removal of the Heat Generator will necessitate conversion to forced flow unless there have been SUBSTANTIAL thermal improvements to the shell AND the experienced occupant has not already complained regarding balance, poor economy, warm basement, etc.

  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    Swampy's right

    The Heat Generator kept a slight pressure on the system so it could carry higher water temperatures. This speeded up the gravity circulation and allowed the use of smaller pipes. If the pressure got too high, it pushed the mercury aside and the water went into the tank. Nowadays we use a closed expansion tank, a safety valve and a circulator to do the same thing.

    Be careful when sizing your circulator. It's way too easy to over-pump these old systems. Follow this link for more:


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  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    If you remove it

    If you ultimately remove it, handle it very carefully and see if a local trade school would be interesting in owning a piece of history before you decide to junk it. I have mine, thanks to Mr. Holohan.
  • Shaun Anderson
    Shaun Anderson Member Posts: 164
    If we can get the mercury out.

    We are in the process of building a hyronic heating showroom and this piece of history would be great to keep and show. Only if we can find a place we could have it drained and cleaned up to display.


  • gerry gill
    gerry gill Member Posts: 3,078
    why not plug the openings

    and keep the mercury in it..thats how mine proudly sits in my reading room.

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    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

This discussion has been closed.