Message from discussion upgrade 3-wire thermostat?
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Mon, 19 Nov 2012 10:21:32 -0800 (PST)
Date: Mon, 19 Nov 2012 12:21:10 -0600
From: "Pete C." <aux3.DO...@snet.net>
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Subject: Re: upgrade 3-wire thermostat?
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> 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?
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.