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2 thermostats 1pump

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rico7467
rico7467 Member Posts: 40
How can I make 2 different thermostats operate the same pump in case they would both signal for the pump to kick on at the same time. What kind of relay or device do I need to operate this situation

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  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
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    Any time you have multiple switches (thermostats) to control the same load, they must be wired in parallel so either one can signal operation. In this configuration, it does not matter if both are closed at the same time.
  • rico7467
    rico7467 Member Posts: 40
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    Right now the thermostats control 2 separate air handlers so if I run in parallel like you are saying is this going to keep the blower on the opposite handler from coming on and which connections should I tap on this thermostat wit the wires that are going to kick the pump on.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
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    Describe your complete application and exactly what you are trying to achieve.
  • rico7467
    rico7467 Member Posts: 40
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    I have 2 electric furnaces in my house for 2 different zones. Each one has 2 thermostats (one set at 70 degrees for the electric furnace in case the outdoor wood boiler would fail and one set at my desired house temperature to run the blower fan) what I am trying to achieve is to only have my circulator run when the house calls for heat because I am only using one circulator and right now it is continously running like most people install these. I just don't know how to achieve that.Right now the blower is connected to red and white so can I tap into a orange,blue,yellow,etc and run parallel like you are saying and it not effect the blower from kicking on in the opposite air handler and what part do I need to transfer that to making that 110volt circulator engage.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
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    What model/brand are the thermostats that currently only control the blower for hydronic heat?
  • rico7467
    rico7467 Member Posts: 40
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    They are Honeywell digital and they are turned on to gas/oil. They are the cheap $20 ones from lowes
  • rico7467
    rico7467 Member Posts: 40
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  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    The "backup" thermostat should be set at a lower temp [than the desired indoor temp].... One should be set for the desired indoor temp and only run the fan (if I understand correctly).

    The other [backup] should be set lower by a few degrees and run the both the fan and circulator.
    rico7467
  • rico7467
    rico7467 Member Posts: 40
    edited January 2016
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    bmwpowere36m3 that is correct but that isn't what I'm trying to figure out. I have two separate air handlers that I am trying to keep separate bur both run the same circulator without short circuiting if they would both call for the circulator to come on at the same time
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    The circulator only has to run when the backup thermostat kicks in, correct? So just wire the two backup thermostats in parallel to the circ or relay.
  • SWEI
    SWEI Member Posts: 7,356
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    How are the thermostats "running the circulator?" Is it wired to a zone relay box, to the boiler, to a fan control?
  • rico7467
    rico7467 Member Posts: 40
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    That's what I'm trying to figure out SWEI I don't know what I need to make them both operate the same circulator without completING the circuit and engaging the blower on the opposite furnace. I don't know if I can use a different stage on the thermostat so it acts like the circulator is the heat pump or auxiliary heat so it doesn't interfere with the blower?
  • SWEI
    SWEI Member Posts: 7,356
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    To what is the wire (metal flex, conduit, whatever) feeding the circulator connected?

    Can you post a photo of the circulator pump along with the surrounding pipes and wires?
  • Eric_32
    Eric_32 Member Posts: 267
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    Does the circulator have a relay powering it or is just hard wired to run forever?
  • Jamie Hall
    Jamie Hall Member Posts: 23,452
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    rico7467 said:

    bmwpowere36m3 that is correct but that isn't what I'm trying to figure out. I have two separate air handlers that I am trying to keep separate bur both run the same circulator without short circuiting if they would both call for the circulator to come on at the same time

    As I read this -- and correct me if I am wrong -- you have two thermostats, A and B, and two air handlers -- 1 and 2. You want thermostat A to run air handler 1, and thermostat B to run air handler 2. You want the circulator to run when either A or B is running.

    So... you need two relays. One with the coil powered by thermostat A/air handler 1 and the other with the coil powered by thermostat B/air handler 2. The NO contacts on both relays are wired in parallel and energize the ciruclator. Coil and contact voltages as appropriate...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    rico7467
  • rico7467
    rico7467 Member Posts: 40
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    Hard wired to run forever that's what I'm trying to eliminate eric
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    To me it sounds like 4 thermostats...
  • Jamie Hall
    Jamie Hall Member Posts: 23,452
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    Got to admit that at this point I am hopelessly confused on what it is that is wanted... and what it is that is to control it...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • rico7467
    rico7467 Member Posts: 40
    edited January 2016
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    Best I could do!
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    hmm…

    You have an electric furnace… i.e, forced hot air? But the wood boiler I assume is suppling hot water. So its like a hydro-air system, but also electric? I'm confused… if it's an electric furnace, then how does the wood boiler work in concert?

    What's the square box with the circ, the wood boiler?

    I think you need to post some pictures of your entire setup and that mystery box/relay (probably best with the cover removed).
  • rico7467
    rico7467 Member Posts: 40
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    There is no mystery box relay!!!! That's the product I'm trying to find. As far as the electric furnace goes that is on a separate thermostat that is set 5 degrees below my blower fan thermostat so it will only come on if the boiler couldn't maintain. And yes the circulator is on my wood boiler
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    So that circulator should run, when the "main" thermostat calls for heat?
  • SWEI
    SWEI Member Posts: 7,356
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    Are you comfortable assembling electronic components like relays, transformers, etc. in a box? Jamie described an inexpensive solution, but there are prepackaged relay controls that would be easier for a non-pro to install.
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    So you actually have more than two thermostats. One for each zone/air handler fan and at least another to trigger the air handler to turn on the heating element.

    Sounds like a two zone relay would work like a taco sr502. Like Jamie said, two thermostats inputs and tie the two circ outputs together in parallel to wood boiler circ.
  • rico7467
    rico7467 Member Posts: 40
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    Jamie hall hit it right on the money with his previous comments on two thermostats and air handlers running the circulator. What kind of coils and relays do I need to purchase to achieve that Jamie hall or anyone that knows what he means
  • Eric_32
    Eric_32 Member Posts: 267
    edited January 2016
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    A Taco SR 502 should do it (I think). Wire each "main" thermostat to it's own "TT" terminals in the SR box. Those wires being from terminals "R & W" in the thermostat. to T & T in the taco box. the wire currently supplying the pump now will get a service switch then power the Taco Box. The pump will connect to both zones C1 and C2 terminals in the Taco Box. As long as there is one source of power to the Taco Box, the pump will run when either zone calls.

    Question... the water from the boiler goes where? Thru a coil in the air handler? or something else? and does it go thru both coils in both air handlers? if So how... in series? meaning through one then through the other?

    They make two stage thermostats.. that have terminals to call on a 2nd stage of heat (your electric element) if necessary if the 1st stage can't keep up. So each air handler can operate off 1 thermostat instead of 2.

    To me it would work like a heat pump as primary heat or 1st stage with electric element in the air handler as the 2nd stage.

    edit.... I just looked at your drawn diagram... I think you would be better off adding a zone valve for each air handler and use a Taco ZVC 403 box instead. This way flow will only go to the hot water coil in the air handler that requires it. and there will be one end switch for the single pump. If it is indeed piped like you have drawn and they are not in series but piped separately back to the "manifold" where the pump is.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
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    Do you have AC tied in with the furnace thermostats?
  • JUGHNE
    JUGHNE Member Posts: 11,077
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    If you want the pump to run whenever either furnace fan is moving air this is a simple idea. Really old school but simple.

    Put a "Sail" switch on each furnace, connect the switches in parallel, switches may have to power a relay based on the pump electrical load. "Borrow" 24 VAC from one of the furnaces to run the relay. 2 wire T-stat cable is all you need for pilot circuit.

    If you have AC, then add a switch for the low voltage so the relay coil isn't cooking all summer.
  • SWEI
    SWEI Member Posts: 7,356
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    Do you want the pump to run after the fan(s) start, or before they start? Blowing air over a cold coil may not be the best plan, which is why they make controls for this (e.g. Taco HAFC-201.) A snap switch will also work, but may already be there in the "furnace" controls (if there are any.)