upgrade 3-wire thermostat?

[bob]

The cable connecting the furnace and thermostat has 3 wires. The thermostat
is a honeywell battery powered unit and can turn the heat on/off, or turn
the fan on/off.

I want to install a thermostat that can be remote controlled, but they all
require an additional C wire, to draw power from the furnace.

Is the only solution to fish a new 4-wire cable from the furnace to the
thermostat, or is there an easier way?

[tra...@optonline.net]

Unless you can find a remote controlled thermostat
that runs only off of batteries, the only solution is a
new cable. And I'd probably make it 6 or 7 wires, so if
you add AC, etc you have extra wires. The cost
diff for the cable is small.

[Pete C.]

Fish a new wire, you may be able to use the old one to pull the new one.
Alternative would be to give up separate fan control, tie them together
at the furnace end and re-use the fan wire for your common.

[tra...@optonline.net]

He could do that, but should realize that if he
does, the fan will come on at the same time as
the furnace. Normally there is a delay of a minute or
so to avoid blowing cold air, before the furnace warms
up.