I've done some research, and here is my plan.
The current wiring for the humidifier is this
Some close up pictures
Furnance control board
Note that the black wires connecting to the C & W1 terminals are for the humidifier
My plan is to disconnect the black wires from the C & W1 terminals in the furnace, and from the valve on the humidifier. Cap and tape the exposed ends of the now un-used black wires.
Then I use this FAS/LVT Copper Thermostat Electrical Cable - 18/2 Brown.
Connect the black to C terminal and the white to the W1 terminal in the furnace
Run it to the humidifier, cut open the overall brown jacket and cut the white wire apart. (the black wire is not cut)
Connect each of the white ends to one of the wires on the humidifier valve.
Keep running the cable to my Ecobee 3, connect the black and white wires to the ACC+ and ACC- terminals on the Ecobee 3.
I have a few questions for this plan.
1. Is the cable I'm using going to be okay for the humidifier?
2. There is no HUM terminal on the furnace control board, will this be an issue?
3. Any other comments and concerns?