Just bought a Honeywell RTH221B T-stat to replace old mercury one on wall. I have a single zone, gas fired forced hot air/AC furnace with condenser outside. Coming out of the wall I have 2 t-stat wires, one has a red and a white, and the other has a blue, green, white and red. All wires were hooked to a terminal in the old t-stat. How do I wire the new one?

Take a look in the furnace. Take the covers off, and look where the wires are hooked to in the furnace. Let me know and we should be able to help you out. If you can post some pics of the wires at the stat, and the wires at the furnace, it would help also.