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Thread: Converting a manual switch heating zone to a thermostat heating zone

  1. #1
    DIY Junior Member
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    Default Converting a manual switch heating zone to a thermostat heating zone

    Hi Everyone,

    I have a split level house that has 3 hot water heating zones that run on a single oil burning boiler; One of the zones is for an exterior greenhouse, which is adjacent to the outside of my house. The circulator for the greenhouse zone turns on using a manual switch, and the temperature in the greenhouse is controlled by automatic ventilation.

    We plan to remove the greenhouse entirely.

    We decided to disconnect the greenhouse supply and return lines, but make use of the existing system by rerouting it to our basement, which previously had no heat. Now I am trying to convert the manual switch for the circulator into a thermostat controlled zone. I understand that I need to install a relay switch and connect that to the boiler, but I am at a loss for what time of switch/thermostat combination I should use, and how to install it.

    Can anyone point me in the right direction? Much appreciated.
    Last edited by breilly629; 03-10-2010 at 07:41 AM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Look at www.taco-hvac.com for a zone controller. This will have a low-voltage control module that a standard thermostat can control and a relay to turn on the circulator. Alternatively, you could pick up a 120vac thermostat and control the circulator directly. Note, your existing system may have an unsed set of contacts that could be used with a new thermostat and no new hardware other than the thermostat and rewiring.

    So, in reality, there's no one standard way to do this, and you'd have to know more details about what you are starting with.

    Just controlling the circulator may not fire the boiler, depending on how that is set up. You'd have to review what you have, and then see what is required to add a zone.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
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    Cheapest way would be with a Honeywell RA845 switching relay. Thermostat calls the relay, relay starts the circ and calls the burner.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    That assumes the boiler is not "constant temperature", but since the greenhouse circuit apparently worked by just starting the pump, the assumption is that the zones are NOT controlling the burner and all he has to do is operate the pump with the thermostat. EIther a line voltage thermostat, (possibly the easiest way), or a switching relay, RA819A comes to mind if my memory is correct after over 40 years of not using one.

  5. #5
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    The old system would have operated on that basis as the boiler would have had to maintain temperature for the greenhouse zone to heat and that same set up would work for the basement zone as well though I am assuming that the house zones control circulation as well as burner operation. A Honeywell RA89 would also serve though it does not have as set of dry contacts to call TT on the primary control or Dual (or triple) aquastat. A Picture of the boiler and controls would be helpful.

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