upgrade 3-wire thermostat?

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?
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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.
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bob wrote:

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.
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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.
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