I want to let my main thermostat control the duct fan. I have purchased an energizer but am unfamiliar with hooking it up to the thermostat.
The energizer has two connections for 24v wires and I would like it to come on
Whether using heat or air.
I know G is the fan control but where should the second wire come from ?

Y? Or RH or RC? Please advise as if you are telling a novice.
Thanks