I have a heat pump with emergency heat function. Changing the old thermostat to a Rite Temp 8010. All the connections corresponded just like the installation manual said. Only question I had was the old thermostat had a black wire connected to an X terminal. The new thermostat, which has 2 AA batteries, said to tape off the X wire from the old thermostat. I did that and everything seems to work fine (didn't check AC today though). I also pulled the panel off the heat pump unit in the basement and the black wire in question above is connected to a C terminal (apparantly the common side of the 24 VAC transformer? I thought I read somewhere that I could go ahead and connect that black wire from C in the basement to C on the new thermostat and extend battery life? Or should I just quit while I'm ahead and leave well enough alone? Thanks.