Look at a Honeywell VisionPro IAQ. It's a great control for a system such as yours. With your variable speed blower, you can set up two stage dehumidification without a dehumidifier. It will also control a powered or non-powered humidifier. Add an outside sensor and it will do so with complete frost protection. Quite simple to install and program. Once you get through the installer setup routine, day to day operation and schedule programming are dirt simple. These are available for very decent prices. Full factory warranty allegedly requires professional installation but for what that costs, you can buy yourself quite a few of them.

don,

Thanks for the response!

I'm assuming the system you described is the VisionPro IAQ model# YTH9421C1002,
which inludes the TH9421C1004 Thermostat and THM5421C1008 Equipment Interface Module.

Do you have an opinion about the VisonPro model# TH8321U1006, which is only a multistage thermostat with dehumidification and some fan control?

I'm not sure about the brand of my humidifier (but I'll check), it plus a dial control is mounted on the air handler itself.

That would be it. There's a new version 2 of that model that supposedly addresses some programming or firmware problems. The second version can be identified by looking inside the touch screen module for the sideways "2" behind the model number

As far as I know, the lesser VisionPro models will dehumidify by overcooling only. The IAQ controls your variable speed blower trim function and if that's not enough, it goes to overcooling. For example, if you set the IAQ to maintain summer humidity at 45%, when the humidity exceeds that limit, the stat invokes your blower trim function and reduces cfm by 15% to slow the air moving across the coil. If your humidity exceeds the set point by more than 5%, (goes above 50%) it goes into overcooling until humidity drops back below 50%. The IAQ should replace your current humidistat that currently controls your humidifier.

The W-R 1F95-391 and Robertshaw T9865i seem to be the only other units that can handle dehumidification by trimming the blower. All others use overcooling. The IAQ is the only one able to utilize both methods.

I have the Honeywell IAQ t-stat as well, and best t-stat I ever had.