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Using G-Wire as a C-Wire for Smart Thermostat

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  • Dec 28th, 2017 11:53 pm
[OP]
Deal Addict
Dec 27, 2013
2232 posts
584 upvotes
Woodbridge

Using G-Wire as a C-Wire for Smart Thermostat

I purchased a Honeywell Lyric T5. This unit requires a C-wire. My home does not have one. I have read conflicting reports about using a G-wire and forfeiting manual fan functionality.

I don't mind not being able to manually turn on the fan. I think I can count on one hand the number of times I've manually turned on the fan. I just want to makes sure that the heating and cooling wire will turn on the fan when the unit is heating and cooling.

This would be a temporary solution while I look into either running a 5th wire, or installing some sort of extra wire module... which goes into my next question:

Assuming that running a 5th cable is not something I'm going to do, what is the best permanent solution to not having a C-wire? I know of the Honeywell Wire Saver Module, Venstar Add-A-Wire. Will either of these work just as well? Are there other options out there that might be better/cheaper/easier to install etc.?

Thanks for the help!

EDIT - the concerns I saw online were that the heating will run the fan without issues but the AC will NOT turn on the fan. This YouTube video suggest running a jumper at the furnace control board between the Y and G, so that when the AC turns on, the fan will turn on. One comment in the comment section suggested that on his Lyric T5, it originally didn't work, but then after some software update/calibration it started to work. This is just one report, but I'm optimistic. Any comment on this?
2 replies
[OP]
Deal Addict
Dec 27, 2013
2232 posts
584 upvotes
Woodbridge
Hmm - Another option is I buy a 5 wire bundle, disconnect all of the wires from the furnace, clamp the start of the new bundle to the end of the old bundle and just pull it out at the thermostat and hope it just pulls its way through the wall. This sounds like a bad idea though... I'm sure something would get snagged along the way.
Sr. Member
Mar 19, 2013
689 posts
205 upvotes
Prince Albert, Sask.
I would leave the existing wire as is. It could be stapled or attached in someway. It may turn into “why did I do this”. Fish a new wire. Sounds like you have access? Remove your thermostat, take some string, attach a weighted object, I use a screw. Drop the weighted screw and string(ample) in the hole where your existing wire is. Locate where the wire comes out. Take a foot of sturdy wire, I use electrical ground wire. A chunk of metal coat hanger will work. On one end of the wire make a hook. Then about 6 inches from the hook, give the wire a 45 to 90 degree bend. Now go fishing, stick the wire in the exit hole and twirl. Your will catch the string. The rest is easy. Worked for our provincial phone company for 31 years, worked every time. Good luck, have fun.

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