I bought this thermostat and installed it myself though Honeywell is quite clear that this is not for homeowner installation. It's my understanding and it's clear from the documentation, that only professional HVAC people are supposed to install this.
Though you can install this without the Equipment Interface Module (EIM), I decided to wait, get the EIM, and then do the full installation. The first EIM I ordered was the wrong one, so you have to be careful about that. The EIM is installed next to your equipment, you run almost all the wires from your devices to the EIM and just a two-wire thermostat wire (for power) to the thermostat itself. Once powered up, the EIM, the thermostat, the outdoor remote, and the handheld remote can all start talking with each other over the air and things are swell from that point on.
I have a forced hot air, oil furnace, an air conditioner, and a powered bypass humidifier. I also got the optional return and supply air temperature sensors. Everything wires into the EIM: the humidifier can use one of three universal terminal pairs. When you setup the thermostat for the first time, you tell the thermostat what you have and what's wired to what ports on the EIM.
I did run into some quirks. When I opened up my furnace to find the power supply, I didn't realize the low voltage thermostat power is actually AC, not DC. I was carefully (I thought) testing everything as I went and ended up confused when I didn't read the voltages correctly on my meter. This was a rookie error. A professional installer would have known immediately that 24 volt AC power is used.
You are given the option of having the thermostat control the humidifier and run it even when the heat is not on. I have not been successful in implementing that option and the thermostat didn't run properly with that option set. Once I put the options back to the more typical situation where the humidifier only runs when the furnace is on, everything ran perfectly.
You have to enter a code to get to the installer options after you first set everything up. This code is not hard to find and if you read the installer instructions carefully, you can find it easily thereafter.
Once in place, the thermostat is excellent. It recovers from lost power without a hitch and no new programming or resetting is needed. The touch screen works very well. The options are plentiful and excellent. You can, for example, hit a button for "Stay home from work" and it will keep the heat on for you. Controlling the house heat using the remote control as your temperature sensor works very well. (I need this as the wall-mounted thermostat is affected when I have a good fire going in the fireplace formerly leaving the rest of the house freezing.)
I'm very pleased with the thermostat though I don't expect any help from Honeywell if something goes wrong.
**************** Update... three months later... ********************
I spent some time going through all the wiring on all my equipment. I found wiring diagrams for the furnace and air conditioner. I got better light into the nooks and crannies and took my time identifying everything on everything. I found it helpful to take pictures of items, load them onto my computer, and then blow them up to see details and to have everything in the same place.
The end result was that I found several places where technicians over the years had swapped wires here and there. Things worked with simpler thermostats but I think these swaps were causing problems with this fancier system.
I took my time, straightened out the wiring for the furnace, hooked it up, tested it, then did the same for the fan relay, then the A/C, then the humidifier. I tested things as I went and made sure I was matching all the wiring diagrams.
Bottom line was that I got it all working beautifully. I mentioned that the thermostat has a code-locked installer section. In that master menu, there are all sorts of sub-menus for setting up and testing the system. In the testing section, you can go through each component one by one and turn them on and off. If you have the sensors, you can check the temperature difference between return and discharge air. This was extremely helpful. There were times I was worried when testing the equipment without using this special testing section... things would work and then they wouldn't. Another rookie mistake on my part. The thermostat won't allow the A/C system to turn on then off and then on again in rapid sequence... that's to protect the equipment from rapid cycling. But that was also causing me to worry something had gone wrong when I couldn't fire things right back up. However, if you use the installer test section, the delay is bypassed and you can turn things on and off as necessary to check it all out.
Soooo.... I'm very pleased with this system. It ain't cheap, it ain't uncomplicated, and it ain't for the timid. But with some patience and skepticism of what technicians have done to your system in the past, you can get it all up and running and when you do, it's really, really good.