So I just paid for a IAQ thermostat and the contractor said it won't control the speed of my Goodman VS 2 stage furnace because the AC is only a single stage system. Is that true? I have read on here that the IAQ was the thermostat to get as it can control VS fan speed. I paid the extra money because I have an existing truezone Honeywell 4 zone system (only using 3 zones). Do I need to return this thing or what?