Questions tagged [thermostat-c-wire]

The "C" or Common wire provides a way to get constant 24VAC power to the thermostat, now required by many newer thermostats with WiFi and/or touchscreens.

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257 views

How to wire isolation relay to create C-wire

I'm trying to follow the ecobee instructions here: https://support.ecobee.com/hc/en-us/articles/227874527-ecobee-thermostat-installation-with-an-isolation-relay Which uses a wiring diagram as such: ...
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Wifi thermostat

Can I connect C-wire to the empty terminal(red arrow)
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321 views

What are these extra wires behind my thermostat?

I an hoping to install a new thermostat that requires a C wire. I pulled off my old thermostat, an old round dial type, and it was of course only connected to four wires. The four wires are the only ...
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321 views

Connect C wire Lennox G16

I bought a new thermostat that needs the c wire. Old thermostat wasnt using the blue c and was stuffed back in the wall. Come to find out the blue c wire is not connected to the furnace. Trying to ...
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203 views

Lennox G16Q3-50 Furnace with AC, Door Interlock Switch and Main Circuit Breaker

If the door of the Lennox G16 is removed, thus the door interlock switch unpressed and system off. Does this mean that I only need to shut off the AC power from the outside breaker panel and leave the ...
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Pull 7- or 8-conductor thermostat cable?

I've got 4-conductor cable now, but am looking to put in a smart thermostat (ecobee3). It requires a C wire, or the use of their adapter kit, so I'm thinking of just pulling new cable. 7-conductor ...
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161 views

Honeywell Wi-Fi Thermostat

I need to hook up a C wire to power a wi-Fi thermostat. I have an extra unused blue wire, but I don't know what to hook it up to at the furnace. I don't have the traditional wiring R W RC G Y C on the ...
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3answers
4k views

How to move from RH/RC thermostat to C thermostat in AC only system?

I see this is a pretty common question, but the answer seems like it might be dependent on your thermostat and air handler, so I'm posting with my specific questions. I'm upgrading from a White ...
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479 views

Where is my Common Wire? [duplicate]

I purchased a wifi thermostat and cannot located the common wire. My unit is old and is a Coleman 70 with no terminals inside labeling the wires. As you can see in the second image, there is a blue ...
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292 views

C terminal / Wifi thermostat [duplicate]

I'm using a blue wire as a c-wire, however when I went to connect the blue wire at the furnace, it already had a white wire ( not from a thermostat) corrected to the c-terminal. Can / wires be ...
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Where to attach the “C” wire to my furnace?

I am upgrading to a new thermostat which requires a "c" wire to power it. I have an unused blue wire running from my thermostat to my furnace that I plan to use as the common wire. However, I am ...
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Where to connect Blue C Wire at old furnace?

I have looked at other responses and each layout is a little different. Looking to connect a Smart Thermostat and need to know where to connect the Blue wire at the Furnace. See the attached picture....
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Heatpump Wiring Color Convention

A heatpump thermostat is to be upgraded. I am unsure of: Which color wire is the Common (thought to be BLUE) Where should the brown wire be connected? (B node?) Is the 'B' node in the photo ...
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61 views

C wire Hooked to Compressor but terminated at Thermostat

I'm looking to install a thermostat that requires a "C" wire. See the picture below of the terminal inside the furnace one of the blue wires appears to go to the cable that goes outside to the ...
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1answer
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How do I create a C wire? [duplicate]

My furnace is old and only has 4 wire connections, but I require a C wire. How can I create one based on this diagram? I do have 5 wires running between the furnace and thermostat.
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Do they make 24v transformers that have individual terminals for up to 4 thermostats? [closed]

I have two ecobee 3 thermostats sharing a 24v transformer. I'm about to buy two more. Do they make 24v transformers that have separate pairs of terminals for each thermostat? This is not a question (...
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C wire problem for WiFi thermostat [duplicate]

I’m trying to add c wire to furnace to run a WiFi thermostat but don’t know where to hook up c wire to get power to turn on thermostati have 2 extra wires just don’t know where to put one them to get ...
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How can I install a Honeywell Wifi RTH6580WF1001 thermostat in place of a Honeywell RTH2300b?

I have separate heating (hot water) and air handler (cooling System). The current thermostat I'm using is a Honeywell RTH2300B and the new one I want to install is a Honeywell Wifi RTH6580WF1001. The ...
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278 views

I have older HVAC unit (heat pump) and looking for the C wire to hook up to Smart Thermostat

I spent 2 hours with Thermostat vendor, Ecobee and they couldn't help me. I have R,G,Y,B and the white lead is not connected. I need some guidance on how to get a Common wire. I tested voltage and R-G,...
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How do a replace an old baseboard thermostat with a wifi thermostat?

I don't know if this is a dual pole or single pole thermostat (n00b here, don't know what I'm talking about). I don't even know what voltage this is (240 or 120). But here's a photo of the wiring: ...
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Help me to find C wire

GV1 - ZONE 1 VALVE GV2 - ZONE 2 VALVE Y1 - YELLOW WIRE 1 Y2 - YELLOW WIRE 2 R1 - RED WIRE 1 R2- RED WIRE 2 TT1 - ZONE 1 THERMOSTAT TT2 - ZONE 2 THERMOSTAT R RED WIRE W WHITE WIRE B BLUE WIRE BOILER ...
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1answer
1k views

Add c wire to furnace for smart thermostat

I have an older furnace and am looking to add a c wire for a smart thermostat. Currently behind my thermostat I have red/black wire, however, there are 3 additional wires that are not connected. At ...
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Why isn't the “C” or Common wire working on my Nest thermostat?

I Have connected the Blue wire to the C terminal on a 3rd Generation Nest and to the Blue wires on the Transformer....... But the Nest Thermostat does not show the Blue wire connected on the Equipment ...
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610 views

how to connect C wire to Weil-McLain EG-65 Series-5 gas steam boiler

Which of the Weil-McLain EG-65 transformer terminal should I use for a thermostat common wire? (I am trying to connect a nest learning thermostat to that boiler and it needs a common wire). Thanks.
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Smart wall heater thermostat line voltage from high to low.

Cadet's blog provided an approach on connecting a smart thermostat to a Com-Pak wall heater by connecting it to a relay/transformer. They have recently updated and changed their post to not recommend ...
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236 views

Installing an Ecobee3 - Wiring Question

This shows what my wiring looks like in the living room and garage. I had a Honeywell Thermostat that I want to replace with an Ecobee 3, is it possible to use the C terminal for this? The red wire ...
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3k views

No C wire connection on old Goodman furnace

I have read for hours, and tried figure this out myself, but I need help. I'm trying to connect the Blue C wire from the tstat, without a C terminal at the furnace. From what I have read, it seems ...
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1answer
399 views

Finding “C” wire on old heat pump HVAC unit

I am wanting to replace my old round mercury filled Honeywell thermostat with a new wifi smart Honeywell thermostat, the only problems is I don't have a "C" wire on my current thermostat and need help ...
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2answers
10k views

Less than 24 volts on the thermostat C wire

We have a brand new air handler at work, but the thermostat is mounted on a wall next to a server/computer room which is always warmer than the rest of the office. I want to install a thermostat that ...
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1answer
522 views

How do I wire a thermostat with an external 24V transformer?

My current wiring has 5 wires, R, Rc, Y, G, and W wires. No C wire. I've added an external 24V transformer and connected one wire to the C connector but don't know what to do with the other. If I ...
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2answers
8k views

What if the furnace doesn't have a C wire connection

I have a 25+ year old York Forced Air electric furnace, want to hook up the new Honeywell WIFI stat, there is no C wire connection in the Furnace itself, and some instructions have indicated using the ...
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605 views

How to wire a C-wire from a humidifier to a Carrier furnace?

I need guidance on a wire. One wire connects the humidistat to HUM. Another wire should go from the humidifier to COM24Vac. My COM is taken as you see in the picture. Is it an issue to wire the second ...
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1answer
523 views

Can I share “C” wire on two thermostats?

I am wiring a second thermostat right next to the original one. The new needs a C wire. Can I share it from the old one? Old: 8 wires, used to run heat pump (w/ heating and AC) and backup oil. Now ...
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1k views

Where do attach C wire on my boiler?

I need to add a C wire to use my wifi thermostat. I have a 2 wire thermostat now. There is a third wire in the wall which runs to the basement where it is cut off. I can easily extend it to the boiler....
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1answer
689 views

Help installing new thermostat

disclaimer, this is my first attempt at doing any type of electrical work, so apologies in advance for any wrong terminology :) I attempted to install a new Honeywell programmable thermostat. When I ...
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4answers
4k views

G to C trick not working for cooling. Honeywell RTH9080WF

My electric furnace has no c terminal. Furnace is heat & cool both. (Lennox Electric Fan coil Model CBS18-21-3P). I installed Honeywell RTH9080WF. I switched G to C on my thermostat and got the ...
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2answers
411 views

How do i connect a Commmon wire to Heat Controller Inc air handler?

I swapped out a 24v Honeywell Thermostat for a NEST Thermostat. I followed the Manufacturer instructions for install. Everything was working for a week or so. I recieved an error(pictured below) ...
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505 views

Is it okay for wires at the C terminal to touch?

I just purchased the Honeywell wifi thermostat but my existing thermostat does not have a C wire. So the instructions given suggest using the G wire as the C wire and at the furnace to move the G ...
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1answer
17k views

Add C wire for Thermostat to Goodman furnace

I have read most of the posts here and have a specific question about my install. In the picture you can see the 3 blue wires coming off the 24v side of the transformer. One goes to the side and than ...
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1answer
2k views

How to add “C” wire using a/c fan wire?

Honeywell has a video that shows how to use the fan wire ("G") of the cooling system as the "C" wire for the thermostat. It is in the video - "Honeywell DIY wifi...substitute g-wire for c-wire" on ...
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1answer
2k views

Where is my common wire on the unit?

I have 2 systems in my house, my heat is gas hot water radiator heating and A/C is a separate newer system. I'm trying to figure out if I can run a C wire off air handler from the A/C system to run ...
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1answer
7k views

Where to connect a c-wire on a furnace with existing two wire mercury thermostat

My existing thermostat is an old mercury two wire device, heat only. Looking to upgrade to a better model, but I need to run a c-wire. I don't know where to connect the wire at at the furnace, any ...
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1answer
1k views

Which terminal should be used for a “C” wire when none are labeled “C”? Older electric furnace/heat pump

I have an all electric air handler/furnace connected to a separate AC unit and it is also a heat pump. I've purchased the latest and greatest Honeywell WiFi "Smart" Thermostat and it needs a C wire. ...
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4answers
14k views

I am installing a Honeywell RTH6580WF with a TACO SR504

The current installation does not have a C wire. So I have run an extra wire and am now confused as to where to connect it. There is a 24VAC connection and a common connection. Comments say that ...
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2answers
4k views

Can I install a Honeywell WIFI Thermostat?

I have done quite a bit of research and have not been able to find an answer I am looking for. I currently have a manual digital thermostat that is not programmable made by Braeburn. My system is a ...
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1answer
4k views

Where to connect c wire at furnace for Honeywell Wi-FI thermostat

We are installing a new honeywell wifi thermostat have an extra blue wire in our bundle. We aren't sure where to connect the blue wire on the furnace board. Click for larger view
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652 views

Please help establishing a C wire for new tstat

I bought a new WiFi tstat as a replacement. The tstat controls my second floor hot water baseboard heat and my central air conditioning. I've located all the wires....the ones coming up from the ...
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1answer
2k views

Need help running and connecting a 'C' wire to my new thermostat [duplicate]

I have a Laars gas boiler that has 3 heating zones; basement, 1st floor, and 2nd floor. I want to replace the old mercury honeywell tstats on the 1st and 2nd floor with newer honeywell RTH9580 wifi ...
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1answer
891 views

How to add a 'c' wire common wire to this system

I have a galaxy cast iron gas boiler and i'm trying to determine where to attach the 'c' wire on the furnace for my new wifi thermostat. The cable is an 18/5 but is only using 2 of 5 wires currently. ...
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2answers
829 views

Do I have to run an extra wire all the way to my new thermostat, or just to the “router”?

I've got an older home (plaster walls) and an older furnace, It's a Peerless. My current thermostat is located on my main floor and only has 2 wires to it, red and white. I should mention that my ...