what if i forgot to label my thermostat wires when i took it off
Back in the olden days, thermostats were unproblematic on/off devices that didn't need their ain continuous power supply. Modern thermostats with Wi-Fi and backlit display, by dissimilarity, need a steady supply of juice.
The C wire, or "common wire" enables the continuous menstruum of 24 VAC power to the thermostat.
Technically speaking, ability flows from the R (red) wire, but not continuously (not on its own, anyway). To make it continuous requires a mutual wire to consummate the circuit. When the circuit is consummate, 24V free energy volition flow continuously.
If you're considering purchasing a smart thermostat, y'all're probably thinking of doing the installation yourself. After all, if you're able to change a light switch or receptacle, you're skilled enough to install a smart thermostat – assuming your system already has a C wire.
If your organisation has a C-wire, it might be in use or but tucked away behind your current thermostat.
If your system doesn't accept a C-wire, you'll demand to run a new cable from your furnace to your thermostat to install well-nigh of the modern smart thermostat models.
Thermostat wire comes in diverse weights. If you accept heat and Ac, you lot'll demand 18/5. If you've only got rut, 18/3 is sufficient just you may want to run 18/5 anyway for a bit of hereafter-proofing.
Identifying Your Thermostat's Wires
There are two means to find out what wires your HVAC organisation has.
Method one: Wait at the wires behind your thermostat
Detach your thermostat from the wall and look at the wires connecting to it. If you've got a wire continued to the terminal labeled "C", y'all're (probably) adept to go with a smart thermostat installation.
If you don't meet a C-wire here at your thermostat, don't presume you don't have 1 merely nevertheless. It might be blimp into the wall, which is what some installers do when the C-wire is present but not needed.
Y'all tin also look within your furnace (see method two). If you discover a C-wire in your furnace, then the other cease is probably stuffed into the wall behind your thermostat.
Method ii: Wait at the wires inside your furnace
Disable power to your furnace and pop the embrace off. (The ease of doing it this way will vary by furnace and installation.)
Look for a row of screws labeled R, C, West, W2, One thousand, Y/Y2, like then.
Every bit you can meet in the photo above, this furnace does not have a C-wire hooked upward. To make this HVAC system compatible with a smart thermostat, it would need either:
- a new bunch of wires run betwixt the furnace and the thermostat, or
- the Venstar Add-a-Wire, or
- a smart thermostat like the ecobee3 which comes with a Power Extender Kit for systems without a C-wire
If the idea of poking around in your furnace or thermostat makes you lot uneasy, consider hiring a professional for the installation of your smart thermostat.
There are no standards for wire colour!Whatever wire can be used for any purpose. A previous owner or handyman may have been "creative", and then what you find behind your thermostat might vary from what you read about online or here. These photos are from my own home, but every home is a unique snowflake.
Here are common uses for wire colors:
- Blue or Blackness – C –Common wire, may be unused by your existing thermostat. Enables continuous power menstruation from the Scarlet wire.
- Red – R – 24VAC power from the furnace'due south transformer
- Ruddy – Rc – 24VAC (defended to heat phone call)
- Crimson – Rc – 24VAC (defended to cooling call)
- Dark-green – G – Fan
- White – W – Rut
- Yellow – Y – Air conditioner
Do I Really Need a C Wire?
Yep, you should install a C-wire if yous are upgrading your thermostat.
Well-nigh all modernistic thermostats, smart or not, require a ability source, and that doesn't await probable to change any time shortly.
Nest Owners Not Exempt
The popular Nest thermostat claims to work without a C-wire, at that place are some caveats. Without a C-wire, the Nest gets its ability from your heating or cooling system… assuming it's running. When it's not running, the Nest notwithstanding needs to get power. The Nest will "pulse" the heat wire, turning on the furnace to pull a bit of power to keep itself going.
In some systems, this is unnoticeable, simply in others, the furnace responds every bit if being told to turn on and and then immediately off.
Read one frustrated Nest possessor's review of his experience with the "pulse" trouble hither.
Nest'south manufacturer updated its literature to warn that the Nest may be incompatible with some unmarried cycle, no-C-wire systems, but the reality remains that outdated wiring is going to get more and more of a pain in the barrel to deal with.
Future Proofing
About states have outlawed the old fashioned "mercury blob" thermostat. Even the most no-frills thermostats on the market today still need a ability source. Adding a C-wire, either through new wiring or an adapter, ensures compatibility with new thermostat technology.
Don't practice the "fan wire" trick
Information technology is true that y'all can re-purpose the fan wire equally a power wire, but then you (and future homeowners who live in your abode) won't be able to manually turn the fan on. If you're going to spend a couple hundred bucks on a thermostat, spend a niggling more than for an adapter or a technician to do the job right.
What to exercise if y'all lack a C-wire
- Rent a pro to run new wires between your furnace and your thermostat (or do information technology yourself)
- Grab a Venstar Add together-a-Wire, which adds a fifth wire to your 4-wire setup
- Go a smart thermostat that's designed to work with systems lacking a C-wire, similar the ecobee3 (information technology has an adapter for C-wireless systems) or the Emerson Sensi (in many systems, it doesn't need a C-wire at all)
Further Reading
- Install new thermostat simply not sure if I have wire C – user mail service and answers on doityourself.com forum
- What is a C-wire? (by Sensi) – peachy explanation past the creators of one of our favorite thermostats
Source: https://smartthermostatguide.com/thermostat-c-wire-explained/
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