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Thread: AHU with Hydronic Heat Coil + Radiant - Need Help with Control Wiring

  1. #1
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    Apr 2011
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    AHU with Hydronic Heat Coil + Radiant - Need Help with Control Wiring

    For A/C, I have a variable speed AHU with a conventional single stage outdoor A/C unit. For heating there is a hydronic heat coil in the AHU heated by a separate boiler. The boiler also heats a radiant floor system throughout the house. The AHU heat/cool system operates well. It was professionally installed.
    The radiant system was installed by me and currently the pumps operate off the relay that also activates the boiler. I want to change that so the radiant-only operates on a stage 1 heat call and AHU+ heat coil operates on a stage 2 heat call. Currently the tstat uses W1 to energize the boiler only and tstat G controls the AHU fan. Tstat W2 is wired to AHU W3. (What function does the have? And thatís where Iím stuck.

    A wiring diagram as it's wired now is attached.

    My inclination is to divert the G wire to a heat sensor on the hot water supply to the heat coil and from the heat sensor to the G terminal on the AHU. Then wire tstat W2 to the relay for the heat coil pump. But this system must exist in a million homes. Can someone please tell me the standard or best way to do it?

    Your help would be greatly appreciated.

    The tstat is a White Rodgers 90 Series
    AHU is American Standard 4TEE3F37B1000A

  2. #2
    Join Date
    Nov 2010
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    DO you have zone valves in place? one for the radiant and one for the fan coil? if not you need to so that the boiler does not circulate hot water though the fan coil and waste good btus that could be going to the radiant.
    It is what it is.......

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