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Thread: Wiring a 3 wire zone valve into existing boiler system

  1. #1

    Post Wiring a 3 wire zone valve into existing boiler system

    Hi - I have added an outdoor wood furnace to my heating system (hot water boiler) and I need to add a zone valve to control the flow of hot water. I have a Taco 572 3 wire zone valve along with their wiring diagram, but it isn't clear how to wire it into my existing system. See my diagram below of my existing system. Can someone explain how to wire this in? Do I need to have a seperate transfomer for this zone valve? What is #3 terminal for? It seems terminal #1 & #2 would do the job.
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  2. #2


    Two wire is for continuously operating pump. Three wire is for intermittent operating pump. You would go by your pump operation.

  3. #3


    So I can't use this zone valve on the existing system?

  4. #4


    Umm... I'm not exactly sure what it is you're attempting to do with the zone valve between these two systems. Quite often, you just have a set of ball valves you switch around when you're burning the outside furnace, and change back when you're burning the inside furnace. Could you explain a little further what you're hoping to do, and we can formulate a little better answer on how to control this zone valve.
    "Nothing is foolproof to a sufficiently talented fool"

  5. #5


    I don't see why you couldn't. Does your circ pmp run continuously? if it does then you need only 2 wires. If your circ pmp runs only when there is a demand for heat then you would use 3 wires.

    I just noticed md's post he posted at the same time I did. To add to what he said. Are you planning on using the outside unit for an undersized inside unit due to room additions or something?
    Last edited by Mr Roboto; November 22nd, 2004 at 10:23 PM.

  6. #6


    Ok...here is what I am doing with the 2 systems. The outdoor wood furnace has a supply and return line. There is a seperate pump on the outdoor wood furnace that will pump hot water to the house boiler and then take the cool water back to the outdoor furnace. This pump runs continuously - I am not trying to control this pump. Attached to the house boiler is my house pump that pumps hot water to my radiators when the thermostat requests heat (so this does not run continuously). The zone valve is placed on the radiator side of the house pump. This is to eliminate the natural convection of hot water from circulating through my house when I don't need the heat (this will also cut down on the amount of wood that I will use). The outside furnace and the house boiler are tied together and use the same water to heat. The outside unit will heat the house all winter (unless I run out of wood - and then I want the inside boiler to take over). I have attached my crude drawing of my system. Hopefully this will help you understand what I am trying to accomplish.
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  7. #7


    So, your wanting to use the house boiler as a standby unit? Then if you run out of wood you want it to shift to the standby unit automatically? Then the standby unit will then become the main heat source with the outside unit becoming idle?

    What is the type of fuel for your house unit?

    From your drawing it looks like you are just using the pump on the outside unit as a circ pump. You have the pmp taking a suction on the house boiler then discharging back to the house boiler. Where does the pmp take a suction from the water jacket?

    It sounds like what you want to do is have the outside unit circulating through the inside unit. The inside unit being idle "as far as a heat source" and the zone vlv controling the heat to the house. Then you want be able to shift the heat source to the inside unit and the outside to become idle.

    Also, do you mean you are using the zone vlv as a stop vlv to prevent natural circulation due to the difference's in densities?
    Last edited by Mr Roboto; November 23rd, 2004 at 09:26 AM.

  8. #8


    Yes, the house will be on standby so that when the water temp in the house boiler gets below a certain temp (measured by the temp probe) the LP boiler will kick in and heat the house system back up to normal temp. Yes, when I am out of wood the house system will take over. The outside unit will still be running but not generating any heat.
    The house uses LP for heat.
    Yes, the outside pump just circulates the hot water from the wood furnace to the house. I am not sure I am following you on the pmp suction thought. Because the wood furnace pump is always running it just circulates the water in the house boiler. The house pump also runs using the water in the house boiler.
    Yes, you are correct on your 4th paragraph. Only planning on shifting to the house boiler when I run out of heat/wood in the outside furnace.
    Yes, the zone valve is only going to open when the inside house pump kicks on. Otherwise it is shutoff - not letting any water move to the house radiators due to natural convection.

  9. #9


    What I meant by the pmp suction on the outside unit. Is that from your drawing it looks like you have the pmp suction hooked to the inside unit return.

    Does the pmp on the outside unit take a suction from the water jacket of the wood burner? Then discharge it to the heating system then returned to the inlet of the wtr jacket on the wood burner?

    It seems that by the way your setting it up. Is that when the outside unit is idle you would be circulating some unnecessary water from the outside unit. This would cause you to use more LP gas when the outside unit was idle. You would be heating that extra water unnecessarily.

    It seems that it would be better to have the outside unit isolated from the system when not in use. You could make it do this automatically if you wanted to. The when the outside unit wasn't being used it would be shut down.

  10. #10
    Unregistered Guest


    Yes, the outisde pump takes water from the wood furnace and discharges it into the inside boiler. The return on the indoor boiler is then pushed back out to the outside wood furnace to be reheated.
    Your are exactly correct! That is the downside to this type of system, but if I don't continue to circulate the water the possibility exists that the outside system could freeze. I don't want that to happen!

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