fluffybear, Honeywell has several vision pro t-stats. The 8100 series is for a 1 heat and 1 cool. This is applied to a system that has a gas furnace with single stage heat and straight ac with single stage cooling. The Honeywell 8500 series will have a t-stat that will have the capabilities of operating 2 stage cooling and 2 stage heating. 16 SEER AC or higher will have 2-stage cooling. Your gas furnace that has a 2 stage gas valve has 2 stage heat. You may have a heat pump which has 1 stage cooling, but 2 stage heating. Model #'s of your outdoor and indoor equipment will help tell us what kind of system you have. Honeywell also goes a step further by providing the Vision Pro IAQ 9000. It operates humidifiers, dehumidifiers, ventilators. It makes no noise because the relays are in a module by the furnace. I have this T-stat, and there is none that compares to it.

I just set my Rheem VS air handler up to control humidity via the IAQ. You don't need anything else, unless you want to do it with absolutely no overcooling, in which case you need a relay. I chose to set it to one degree of overcooling instead, which is the lowest the IAQ goes. Rheem's ODD (On Demand Dehumidification) line works bassackwards compared to the rest of the industry, so you have to set the IAQ up as if you wanted to use overcooling to control humidity in order to get the DHM terminals to switch the ODD line properly. The IAQ could have a whole lot better programming interface. BTW, the crew that installed my equipment apparently didn't have a clue how to wire it for ODD, and just left it unwired, even though I told them the main reason I wanted the VS AH was humidity control. The good news is Rheem's ODD works wonderfully. It really drops the humidity when it comes on. I think you need the 9,000 series IAQ to do the ODD, but I don't have my paperwork handy to verify that.

You will probably need to call Carrier tech support and see how they want you to do it but I am pretty sure the scenario you are suggesting will not work notice they are asking to use an open on humidity increase open and close switch and this switch is just taking the normal cooling setting G terminal out of the control loop at your determined high humidity set point so as to decrease fan speed and result in longer run time for your cooling cycle I don't believe that is what the dehumid 2 function does on the IAQ of course I don't have the installation manual in front of me so I may be wrong but just remember that you are not looking for a 24 volt signal the G terminal will already have that at the call for cooling they just looking for a high humidity setting to open that signal to the G terminal and allow the furnace to go into lower fan speeds Here is a link that might be useful: Air Conditioning Repair made Easy

Location is Northern Virginia and the house built in 1987 with decent insulation. Our new system is a replacement for the 27yr old dinosaur trane which I was told rated probably at 7 or 8 SEER. No dampers in our air duct, all three levels have good air returns but having a 4 ton air handler may be a bit too much. As far as humidity control, the TAM7 is doing a great job so far and very quiet, not sure how is the 4 ton air handler that you suggested going to be better? I'm going to stay far away from Nest, it's terrible from what I've read. What is the model# of VisionPro IAQ? to add wireless remote sensor on all three levels of our home for the VisionPro IAQ I would have to spend big bucks on a Redlink gateway along with the more costly wireless sensors though....