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Tommathome 04-03-2011 02:30 PM

Need Help with Radiant + AHU Heat Coil Control Wiring
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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 low mass 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 operates off the relay that 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. (That doesnít make sense to me even though it works. Does the W2/W3 connection even have a function? And thatís where Iím stuck.) A wiring diagram is attached. It doesn't show the wiring for the A/C for simplicity.
My inclination is to divert the G wire to a heat sensor on the 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

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