C-Wire for Smart Thermostat

[Plump]

Ordered a smart thermostat through the local power company with a $100 instant rebate. Getting my ducks in a row and want to start with the wiring. I've got an OLD house (1895) with just two-wire thermostat wiring to my gas fed boiler. No AC, no fan.

Can I pull a new 4/5 wire and just connect it to the C-wire that's in my current boiler. Nothing is attached to it at this time. Don't want to fry the board and figured you guys would know.

Thanks!!!!

 

[SethB]

Yes you can

 

[jlv03]

It is interesting that, what I assume is the thermostat 2 wires, one of the thermostat wires is landed on the "G" terminal. This is typically used to turn on the fan.

 

[Plump]

It is interesting that, what I assume is the thermostat 2 wires, one of the thermostat wires is landed on the "G" terminal. This is typically used to turn on the fan.

I know absolutely nothing about these wire ups so I couldn't fathom a guess on why they used that G wire. It's a boiler so definitely no fan. I should have the HVAC guy come out to do a check up anyway so I'll maybe get an answer from them.

Thanks!

 

[exranger06]

Yes, I just did this earlier this year on my oil burning boiler. You really only need 3-wire thermostat cable, not 4 or 5.

 

[rlitman]

Yes, I just did this earlier this year on my oil burning boiler. You really only need 3-wire thermostat cable, not 4 or 5.

I agree, but the "you really only need" argument is also why the OP now has to run a new wire, because before this smart thermostat, he really only needed two wires (the same boat I was in).

When I ran new wires to my thermostats two years ago, I used 8-wire thermostat wire. The price difference between that and 4 wire was insignificant (especially compared to the effort required to run the wires). Granted, I happened to have certain walls open that would end up closed, so adding wires in the future would be even more difficult for me.

In my kitchen, I'm piggy-backing that run, by using two of those wires to power a cordless phone base station on the other side of the wall (sending the 9VDC over the wires so I don't need to have the phone plugged in right there). Upstairs, I've got 7 spares (the original 1-pair wire is still there too) that I don't know what I'll do with, but they're not in my way...

 

[brewchief]

I know absolutely nothing about these wire ups so I couldn't fathom a guess on why they used that G wire. It's a boiler so definitely no fan. I should have the HVAC guy come out to do a check up anyway so I'll maybe get an answer from them.



Thanks!

It goes to the G terminal because they are using a common fan center for the circulator relay, very common with older boilers.

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