Last night I only had a few minutes, but I wanted to check the wiring on my existing thermostat. As it turns out, there are only two wires going to it. There is one going to RH and one to W. This is just enough to run a heating system (with no fan control).
However, the cyberstat requires at least one more wire, and an additional wire to just run the fan would be a nice addition while I'm at it. It requires a C wire to power the thermostat, and hooking up a G wire will allow me to run the fan at will. The thermostat has no battery backup. This is likely the case because the wifi probably eats up more power than a normal programmable thermostat. Thankfully, backup power isn't required because the cyberstat uses flash memory. So, once the power comes back on, the thermostat just resumes the program.
Anyway, it looks like I need to run new wire to the thermostat. I am thinking some leftover network or telephone wire (6+ conductor) that I have laying around will work nicely.
For reference, here is what the letters mean:
