Hello, I am attempting to connect my Aprilaire 700 with Automatic Humidistat up to my Honeywell THM5421R EIM, so that the Humidifier can be controlled by the Honeywell EIM/Thermostat. The schematics may be seen on page 10 here: https://customer.honeywell.com/resources/Techlit/TechLitDocuments/69-0000s/69-2758EFS.pdf


I currently have the humidifier functional and powered by it's own solenoid, and I hooked the humidifier up to the furnace's HUM ports and its own outdoor thermostat, but I have no wiring going to the thermostat directly from the Humidifier. It appears that I need to connect the Humidifier to the U1 ports on the Thermostat, without a jumper, since it is already receiving power. I'm just not sure what exactly to connect to the U1 ports on the thermostat, so that I might control the Humidifier from the THM5421R / Thermostat. Is it necessary for me to remove the Aprilaire Humidifier's Humidistat and instead must it be plugged into only the furnace board / Honeywell thermostat? Since it is otherwise functional, ideally, I am hoping the Aprilaire humidifier it can be left wired into the furnace as is, but that it can just be connected to the Honeywell EIM so I can have both controllable from the one Honeywell thermostat. Any help would be greatly appreciated!