Question on wiring relay / Navien NCB fan cutoff to AH

giantsean

Hi Everyone,

Posted here quite a bit last season with a bunch of problems w/ my hydro air setup. Happy to say it's doing better after some tweaking, but it still has a ways to go. For now it's keeping up. On that note, I'm digging into another tweak to solve the problem of the air handlers (one in basement, one in attic) blowing cold air while the our Navien combi is busy on a DHW call (during which it will not supply heating water).

I lifted the attached diagram from the manual. It appears simple enough - 24v from the stat passes through these terminals and in theory (I have not tested yet) the boiler will interrupt the heat call while supplying DHW. Since I have three thermostats (2 zones down, 1 up) and two AH's which need to be cut off, I figured on having to use a relay, but I am having some trouble envisioning the best way to wire the whole setup. Can I take 24V from anywhere (even the boiler itself has a feed as you can see from the diagram), attach to the T/S block, then run a wire from the A/H block to a relay coil, then use the relay to interrupt W on the each air handler? If that will work, I assume I will need a SPDT 24V switching relay. There seem to be a lot of different choices, so appreciate any suggestions. Alternatively if my approach sucks, I'd love to hear about the best way to accomplish this

Thanks and happy holidays!