we are trying to install a new hunter thermostat (42122). We have labeled our wires as directed except we have a brown wire that was considered x in the old thermostat. We don't know where to put the brown wire. Is it considered a common (c) wire?

x goes usually to x or L but is not needed. I take it you have a heatpump and 8 wires at the stat?

There are 7 wires hooked up. There is a blue wire that wasn't used in the old mercury thermostat

well usually blue goes to c, and x like I said goes to x or L. you can take the door off downstairs to see if the blue is hooked to anything, or what the brown wire goes to.

Thanks