You need a thermostat with A. isolated relays, has primary and secondary heat relays ( W1 and W2 ). Because both units have different power supplies you will need either a zone controller or a separate relay. There is absolutely no reason to use more than 1 TSTAT.

If you are only going to use Y1 for cool and W1 for heat you may not need to do anything other than connect the unit. If you are adding central Air to your radient heat you can may only need to increase the wires at the TSTAT.

For example, you need to power the TSTAT. I prefer to power the unit separately from the HVAC system. You contractor will protest, but it is done. It will cost you about 40 dollars for the transformer.

Then you will bring power from the AC system in to RC and power from the heating system into RH. Wire W1 and Y1 to the heating and AC systems and you are done.

If you have W1 and W2 you will need either a zone controller or a relay to isolate the the different power supplies. You only have a single RH so W2 needs to be isolated from the secondary heating system.

April Air does make a TSTAT that can meet these requirement. But there are a number of TSTATs that have these features. Interestingly, I've seen lots of Crestron TSTATs installed by HVAC contractors that will never be hooked up or controlled by a Crestron system. Why? It can control any digital system, from FCU, forced air, or heat pump without needing a zone controller. It also has Y1, Y2, W1, W2, B,O, Humidity relay, and temp sensor inputs. This means a single TSTAT can be installed by that contractor without needing expensive zone controllers ( 300 ).

Alan