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Heating Zones and simple relay?

Discussion in 'Electronic Basics' started by OceanGeek, Mar 27, 2007.

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  1. OceanGeek

    OceanGeek Guest

    I have a house with 5 heating zones, some radiant heat some cast
    iron. Each zone is controlled with a standard 24V thermostat. I
    would like to create a simple circuit that would make a zone (or two)
    slaves to another zone.


    Zone A calls for heat (thermostat closes) i would like this action to
    cause Zone C to come on (via a relay??) for as long as Zone A needs
    heat. Zone C would still be a discrete zone.

    Does any of this make sense?
  2. Rich Grise

    Rich Grise Guest

    Sure. Just energize a relay with zone A's 24V, and put its contacts
    in parallel with zone C's own thermostat output.

    This is assuming ordinary bimetal thermostats - if they're electronic,
    then we'd need more information (i.e., make, model, wiring diagram,
    overall wiring diagram, etc.)

  3. OceanGeek

    OceanGeek Guest

    The other thermostats are electronic but they run off batteries so
    they are really just a switch, right? Will the 24V circuit have
    enough mA to close the relay? I dont want to start blowing the fuse
    (1A) on the control box. Am i over thinking this?


  4. ehsjr

    ehsjr Guest

    Do this - it places no load on your control box:

    AC in----o--- < existing zone A switch
    | |
    [ZoneALoad] [new relay]
    | |
    AC in ----------+

    Pick a relay whose coil voltage matches the
    AC applied to the zone A load (a circulator,
    I assume, but it doesn't matter).

    When zone A turns on, the relay will energize.
    Wire the contacts of the new relay in
    parallel with the zone C switch, like this:

    o--- < new relay contacts
    | ^---o
    AC in----o--- | < existing zone C switch
    AC in ----------+

    You can slave any number of zones you want.

  5. Rich Grise

    Rich Grise Guest

    You're not overthinking it at all, but to come up with a realistic
    answer, we need to know exactly what you have now. It's impossible
    to tell from here how much current your 24V supply can supply unless
    you tell us, and that sort of thing.

    Do you have model numbers, manufacturers, specifications, etc?

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