Humidifier with multi zone HVAC Controller

[hart2hart]

I've got a HVAC unit controlled by a multizone controller -- in my case a main living area zone and a master bedroom zone. The main living area thermostat has a humidity sensor and controls large central humidifier. When humidity is needed the thermostat signals the humidifier to turn on and turns the fan on for that zone.

 

The humidfier runs almost full time during cold weather so I turn fan mode of master bedroom thermostat to On. This method ensures humidified air is sent to both zones of unit. However, during late fall and late winter, the humidifer runs alot less. Finally decided to program so master bedroom fan is only set to On mode when humidifier is running.

 

I've confirmed the Venstar thermostat with Insteon attachment does not send a Fan ON state or mode to ISY when it is turned on as a result of request for humidity. I've reviewed low voltage wiring between Honeywell HVAC controller and humidifier. HVAC person used a low voltage (24V) AC wire from Honeywell HVAC multizone control unit to control a standalone relay and wires from that relay act as Dry Contact so that closed state is humidifer on and open state is humidifer off. My first guess is to install an IOLinc in series with the wire controlling humidifier and have IOLinc send open/closed state to ISY program which will set master bedroom thermostat fan mode (including ignoring if an Override is set via KeypadLinc button).

 

Anyone else have similar setup or otherwise have suggestions? BTW and FWIW, I remember that HVAC person had to call Honeywell to arrive at this configuration for controlling humidifier with Venstar thermostat.

 

Thanks

[hart2hart]

Finished installing a couple days ago and just in case it will help anyone else...

 

The HVAC people had installed a SPST relay. I measured small voltages from the humidifier contacts and the IOLinc sensor contacts. Didn't want these voltages to interfere so I replaced relay with a SPNO/SPNC (SPDT would work) version. When 24VAC is sent from Venstar thermostat SPNC relay contacts are opened and SPNO contacts are closed. The closed set (SPNO) turns on the humidifier and the open set(SPNC) is wired to IOLinc.

 

Simple program logic is:

 

if IOLinc Sensor = Off

master bedroom thermostat fan mode = On

else

master bedroom thermostat fan mode =Auto