I am looking for an automatic humidistat, wall mounted to control an Aprilaire 350. The stat that comes with the unit is cheap junk, and I am tired of adjusting it based on out side temp. No problem running wires for an outside sensor or cont. 24vac power.( Aprilaire says they don't have one other than duct mount.)
Try www.customer.honeywell.com, and follow the prompts for humidity controls. I believe there are thermostat/humidstat combination units, and stand-alone humidistats. The VisionPro IAQ model has humidification controls, and a lot of other features, if it is still available. Some may not be available at retail. Other manufacturers may have similar units as well.