It's not too hard. You need an 8870 per hvac zone(however many tstats hvac guy wired for), an 8811 protocol adaptor and if more than 1 stat, the 8818 distribution panel. The 8870 will wire like any other unit as far as the hvac contractor is concerned. It also has some com terminals that you need to hook your cat5 to and on the other end it will connect to the 8818 and then to the 8811. Basically the tstat is the bridge between the furnace and your XP8 or any other control processor.

We always give the tstats to the hvac guy and tell him to install them without the cat5 so they can get their system fully functional to prevent the blame game of who is at fault when something doesn't work. Then once they are done, we connect the cat5 and take it from there.

If this helps, here is some reading for you [Link: aprilairecontractor.com]