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Multi-stage heating thermostat

How do these work? Are they simply controlling a couple of separate heating systems, and turning them on at the same time, or are they staging them, so that if #1 is unable to handle the load, (and the temperature drops x degrees); then the thermostat fires#2?--NBC


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,495
    edited January 2014
    Types of 2-stage thermost

    I did some research and I see that some thermostats rely on a timer to energize the second stage, which I don't want. If I can find it, I need one with two set points a degree or so apart. Each set point will control a different boiler.

    When the temperature is not too cold, then the first set point will energize the lead boiler, and it should be able to keep up with the heat loss, as long as the outside temperature is no more than 40 degrees below the interior. This system will be sub atmospheric, and so the boiler can be matched to the load at the time, and may run for long periods of time in certain conditions. If the temperature were to drop further, then boiler #2 will be fired as well to help out.

    The aim is to keep the lead boiler able to operate in vacuum in moderate weather, and in periods where the setback temperature will be within the 40 degree difference.

    If I were not using sub atmospheric operation, then I could simply stage them on pressure with the lag boiler cutting out at a few ounces, but I think this means it will fire unnecessarily on a call for heat, which I want to avoid if possible.

    It's easier to put the engine in the bus, than it is to find the right driver!

    Any thought about makes of thermostat I could use??

    Several years ago we had the excellent services of [email protected] on this site to aid us in deciphering the different models of their products-how I miss him! I wish more of the Mfg's were able to have someone answer questions here. I suppose they do not want to get caught up in a ****-fest from some disgruntled customer.--NBC
  • Zman
    Zman Member Posts: 6,792

     I have done what you are attempting with low mass and high mass radiant panels.

    This t-stat will let you set the differential at which  the second stage fires.

    Anther thought would be to use one of these to control the second boiler

    I am not a steam guy, but I think I understand what you are trying to do.

    Will the one boiler have enough capacity to provide an even distribution (ie steam to all radiators)?

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    I don't

    know how techy you are but a PLC would do the job perfectly. You can customize it to do exactly what you want.

  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,495
    Not that techy

    Yes we do need one electronic control for steam boilers, handling, LWCO, pilot lighting, burner lighting, pressure regulation, and temperature control with or without an outdoor sensor, and steam arrival sensor. This would reduce the multiple gadgets on the boiler to just one, connected to a wifi network for control and monitoring.

    I'll have to wait until Mark and his Midco burner are ready for prime time consumption, either as a kit, or a finished product.--NBC
  • vaporvac
    vaporvac Member Posts: 1,520
    Honeywell wireless

    Hi Nicholas,

    I somehow missed this post. My Honeywell 6500 series is meant to do this. It's the system Jstar has used for staging his multiple-staged boilers. Email me if you're interested in the wiring diagram. They are used with a Taco switching relay.
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF