[SGVLUG] HAK group question: How to remote control a millivolt thermostat (circuit)

[Homan Chou]

I haven't been able to attend the HAK meetings yet, let me know if there is
a more appropriate forum to ask my question.

My home (built in 1945), has an old "gravity" heater, which is basically a
gas furnace under one central vent located in the middle of house under the
floor.  There is no forced air distribution at all, the hot air simply
rises up the vent, and pretty much all of it goes up stairs and not into
other rooms downstairs.  That's actually fine because we only need the
heater in the middle of the night for a few hours, and all our bedrooms are
upstairs.  However, the thermostat is located downstairs and is too far
from the vent in order to operate as an effective switch (it's in the
dining room which pretty much stays chilly even if even if it's blazing hot
upstairs.)

I would like to turn the heater on or off based on the ambient temperature
upstairs.

I removed the thermostat cover and it is just a metal coil that expands and
contracts, with a little magnet at the end that snaps onto another piece of
metal to close the millivolt circuit.  That explains why the thermostat is
not very precise at switching on or off, the magnet holds onto the
connection longer than it needs to.

The way I see it, there are 2 problems that need to be solved:

1) I need to be able to remote control the opening or closing of the
millivolt circuit.  a) I can do this manually by attaching an arduino +
servo arm to move the existing thermostat temperature lever.  or b) bypass
the thermostat entirely using some kind of relay?  But I don't know enough
about relays ... what kind, how would it be wired up?

2) I need to be able to forward the ambient temperature upstairs to the
arduino controlling thermostat downstairs.  How do I do that?  Is there a
wireless temperature sensing product I can purchase and hack?  Or do I just
get another arduino upstairs, get ambient temperature using a thermistor,
then wirelessly forward the measurement to the other arduino using a pair
of xbees?  I have never used xbees before.  Should I consider wifi internet
shields instead?  That way I can potentially also control the heater with
my phone/browser?

Thanks for any advice.
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