OK, I have the Lennox XC21 with VS Blower. I also have the Harmony III Zoning system. The (2)T-STATS that control the upper and lower "zones" are for A/C only. The heat is on a different T-STAT. Home came that way. My question for you is is a certain T-STAT required to get the benefits out of my system? If so, which one is recommended? THANKS IN ADVANCE!