Thermostat Wire Color Codes

This article describes several tricks of the trade used by professionals when installing room thermostats and wiring them up. It describes the standard wire color conventions for HVAC thermostats.

Thermostat Wiring Tips & Color Conventions for 24V Thermostats

Complete guide to thermostat wire color code convenions + 9 Wiring Tips for Room Thermostats: Helpful Pointers Regarding 24V Thermostat Wiring & Heat-Anticipators

For HVAC technicians and others who need to determine wire color code conventions & connections for both new and older heating and cooling equipment, heat pumps, split systems, etc., here we give themost-common conventions for identifying or connecting thermostat wires based on wire color and wiring terminal identification letter(s).

Watch out: The type of heating system installed determines what thermostat wires are necessary and how they must be connected. You will always want to follow the instructions from the manufacturer of your specific thermostat or heating or cooling equipment directly as often the wire color and connection points will vary from "standard" conventions.

Our complete thermostat wiring guide for various types of heating or cooling systems and thermostat brands and models is found

at THERMOSTAT WIRE CONNECTIONS.

Additional wiring details are

at THERMOSTAT WIRING DIAGRAMS if you prefer those.

Article Contents

• THERMOSTAT WIRING COLOR CODES - you are here
• BASIC THERMOSTAT WIRE COLOR CODES - heating and cooling with electric, gas or oil heaters
• THERMOSTAT WIRE COLOR CODES - CURRENT heat pumps & combination systems
• THERMOSTAT WIRE COLOR CODES - TRADITIONAL heat pumps & combination systems
• TIPS on THERMOSTAT WIRING & COLOR CODE CONVENTIONS
• SHORTING THERMOSTAT WIRES to ID R W B
• SHORTING THERMOSTAT WIRES -> NO HEAT

Also see HVAC SYSTEM TYPES, and see for our complete guide to wiring different types of heating, cooling systems & various brands and types of room thermostats.

Basic Thermostat Terminal Wiring Color Codes

Notes to the table above

As shown these thermostat wire connections are for a heating only or heating and cooling system (not heat pumps) using a single 24VAC transformer for power.

• Y = A/C, may be routed from the thermostat to the air handler (blower unit for indoor air) and from there to the A./C compressor/condenser unit (outside)

Newer HVAC systems and thermostats may sport additonal terminals by convention used as follows:

• Rc = cooling - takes power to the cooling system; may be jumpered to R in single-transformer systems; Not jumpered if using a separate transformers for heating & cooling systems
• Rh = heating - takes power to the heating system; may be jumpered to R in single-transformer systems; Not jumpered if using a separate transformers for heating & cooling systems
• G = fan, possibly switched by the thermostat's FAN ON control if present
• C = common, brings 24VAC power to the thermostat to power various features

Contempory Thermostat WIring Color Codes - heat pumps

Notes to the table above

This table shows the most-common thermostat wire connections on modern combination heating and cooling and heat pump systems.

1. O wire for reversing valves in Amana, Carrier, Ducane, Goodman, Heil, Janitrol Lennox heat pumps, may vary for othe rmanufacturers
   
   Dark Blue wire for reversing valves on Rheem & Ruud heat pumps
   
   Also referred to as "changeover to cooling" relay
2. Y2 wire for stage 2 cooling may be colors than light blue
3. W2 wire for stage 2 heating may be other colors than brown

Traditional Thermosat Wiring Color Codes

Notes to the table above

This table shows typical thermostat color codes and connections for a traditional heating and cooling system including some heat pumps and backup-heat systems.

Tips for Successfully Wiring a Room Thermostat for Heating or Cooling

1. The string in a typical recently manufactured multiple element thermostat wire is there to help an installer more easily strip off the main outer jacket without harming or nicking the individual inner wire jackets.
   
   Once an installer has used a knife or wire stripper to expose enough of this string to be able to grab onto it with his fingers, he can then pull the string at right angles to the thermostat wire, then slicing easily a little further through the main outer jacket without having to risk any further harm to the new just freshly exposed jackets of the smaller inner wires.
   
   An installer can then simply prune away any of the smaller wires which he may have had to nick before he was able to grab onto the string and to use it to safely strip off the outer jacket.
2. It's always best to wrap a spare or unused wire around the main thermostat wire outer jacket where the outer wire jacket just starts, so that such wires, if needed, could still be used at a later time or date. C
   
   utting such wires back instead of merely wrapping them back out of the way, may be regretted later on in the job in hindsight. We don't leave bare wire ends because we don't want to risk accidentally shorting out something inside the thermostat or other control device.
3. Heat-anticipators are typically chiefly found in mechanical (non-digital) thermostats, though some new digital / programmable room thermostats like the 3M-22, discussed
   
   at THERMOSTAT SWITCHES, INTERNAL, provide a nearly identical function referred to as an adjustable thermostat swing-rate (cycle rate or thermostat sensitivity).
   
   Whenever installing or servicing a thermostat with a heat-anticipator, the amperage setting on the heat-anticipator should always be verified as matching the amperage draw on the gas valve or relay that it controls.
   
   See HEAT ANTICIPATOR Adjustment
   
   and HEAT ANTICIPATOR SET & TEST by AMMETER
   
   Not all heating systems and buildings benefit from a heat exchanger but in some cases you want a thermostat with this feature.
   
   See DO I NEED A THERMOSTAT WITH A HEAT ANTICIPATOR? for details.
   
   In any event, if a heat anticipator is included in a thermostat it should be set properly. Otherwise the relay or thermostat may not function properly, resulting in too-short burner on-time (higher heating costs) or room temperature overshoot (wasted heating dollars).

   Note: your fuse marked with an "E" was probably being read upside down and was a 3-amp fuse. Using a fuse one amp greater incapacity is probably not too dangerous, but it's best not to overfuse as doing so risks equipment damage. Certainly a larger fuse is asking for wiring or device burn-up should a future short circuit occur. - Ed. & reader comments

   Since shorting thermostat wires can damage a circuit but can also blow the low voltage transformer, also

   see LOW VOLTAGE TRANSFORMER TEST

   Reader Question: possible shorted thermostat wires

   Our furnace thermostat failed after an adjacent water heater installation. I noticed that wires were pinched between the water heater and the gas pipe. After I loosened the safety straps and freed the wire, the thermostat works. (I reset the furnace). Were squished wires the cause of a temporary short and will the wires keep working if they are undisturbed? - Larry 8/2/11

   Reply: check for shorted wires and for thermostat transformer damage as well as for blown fuse

   Yes it's surely possible that your thermostat wires were shorted. Now a short in those wires sometimes lets you off the hook with no trouble, since the wires and thermostat are basically an "on-off" switch that calls for heat (or no heat).
   
   But a thermostat wire short at the transformer could burn out the low voltage transformer that powers the thermostat and heating controls or maybe even damage the thermostat itself.
   
   Find and check the low voltage transformer (often it's mounted near your furnace, on an electrical junction box, or it may be integral in your heater control unit).

   See LOW VOLTAGE TRANSFORMER TEST

   Question: reader comments on shorting out thermostat wires & fusing requirements

   Greetings, not sure if anyone saw this or not, but whoever S.R. is above in the description about shorting out wires seems to maybe have missed the fact that the "E" they refer to is actually a "3" amp fuse and not a 4 amp fuse.

   My HVAC installer of 30 years who recently installed 2 furnaces for us and is installing my heat pump agrees that it is a 3 amp fuse. We purchased an extra one just in case. Putting a 4 amp in there may not be good for the board as it may allow too much current for a relay or something and you may fry a piece on the board which is most likely not cheap. I hope this helps - D.M. - 3/12/12

   Reply:

   Thanks D.M., We posted your important fuse size comment right in the article

   at SHORTING OUT THERMOSTAT WIRES - Leads to Loss of Heat.

   ...

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   Reader Comments, Questions & Answers About The Article Above

   Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

   Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

   What type & brand of thermostat do I buy for "heat only" ?

   I see red/white/blue&white.
   
   I need to find a thermostat to operate steam heat only.

   No AC or Fan while using these wires.

   Wiring from 60s, radiator is cast iron, new boiler.
   
   The Braeburn Megaswitch was installed to replace old round Honeywell. Now no longer sets, ( coil retracts back to center and heat is coming from all radiators)

   I purchased new non programmable heat only round Honeywell w/o anticipator but has on/off switch in back
   Did not work
   
   The wires - what type of brand thermostat can I use. On 2021-01-03 by Victoria

   by (mod) - Braeburn 505 "Heat only" thermostat

   Victoria
   
   A Braeburn 505 "Heat only" thermostat will work fine for you and is very inexpensive.

    

   ...

   Continue reading at THERMOSTAT INSTALLATION STEPS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

   Or see THERMOSTAT WIRING TIPS & COLOR CODES FAQs - questions & answers about TT wiring posted originally at the end of this page.

   Or see these

   Recommended Articles

   • THERMOSTAT INSTALLATION STEPS
   • THERMOSTAT WIRE CONNECTIONS
   • COMMON WIRE at THERMOSTATS
   • CONVERT LINE to LOW VOLTAGE THERMOSTAT
   • LINE VOLTAGE THERMOSTATS
   • THERMOSTAT WIRE CONNECTIONS - 2-WIRE like the T87F
   • THERMOSTAT WIRE CONNECTIONS - 3-WIRE Red, White, Blue Wires
   • THERMOSTAT WIRE CONNECTIONS - 4-WIRE Red, Yellow, Green, White
   • THERMOSTAT WIRE CONNECTIONS - 5-WIRE Blue/Black, Red, White, Yellow, Green
   • THERMOSTAT WIRE CONNECTIONS - 6-WIRE Red, White, Blue, Yellow, Green, Orange Wires
   • THERMOSTAT WIRE CONNECTIONS - 8-WIRE Black, Red, White, Yellow, Green, Orange, Brown, Blue
   • THERMOSTAT WIRE SORTING to ID R W
     
   • THERMOSTAT WIRING AZEL i-LINK
   • THERMOSTAT WIRING 3M-22 FILTRETE
   • THERMOSTAT WIRING AMERICAN STANDARD
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   • THERMOSTAT WIRING EMERSON
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   • THERMOSTAT WIRING GOODMAN
   • THERMOSTAT WIRING & MANUALS, HONEYWELL
   • THERMOSTAT WIRING LINE VOLTAGE 120-208-240VAC
   • THERMOSTAT WIRING NEST
   • THERMOSTAT WIRING TRANE HVAC
   • THERMOSTAT WIRING WHITE RODGERS
   • THERMOSTAT WIRE TERMINAL ID CODES / FUNCTIONS
   • THERMOSTAT WIRING OPENING SEAL
   • THERMOSTAT WIRING COLOR CODES

    

   Suggested citation for this web page

   THERMOSTAT WIRING COLOR CODES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

   Or see this

   INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC THERMOSTATS

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   Citations & Reviewers

   In addition to any citations in the article above, a full list is available on request.

   • [1] ...
   • [2] Thanks to reader S.R. for discussing loss of heat due to a thermostat wiring mistake, October 2010
   • [3] Thank to Mr. Scott Meenen , G&S Mechanical Services , for providing some common thermostat wiring codes also found at Mr. Meenen's web page Malware Deleted 12/9/2014 . Mr. Meenan provides heating, heat pump, and air conditioning repair services in Maryland, Washington D.C., and northern Virginia. He can be contacted at 301-591-1646 or by Email to Malware Deleted 12/9/2014 - 10/2010.
   • [4] Azel Technologies Inc., P.O. Box 53138 10 Royal Orchard Blvd. Thornhill, Ontario, Canada L3T 7R9 Ph: 905-223-5567 Fax: 905-223-3778 Email: info@azeltec.com, Website: www.azeltec.com.
   • [5] Honeywell Controls, the company wants you to use their contact form at this web page: http://www51.honeywell.com/honeywell/contact-support/contact-us.html
     Honeywell Consumer Products, 39 Old Ridgebury Road Danbury, CT 06810-5110 - (203) 830-7800
     World Headquarters, Honeywell International Inc., 101 Columbia Road, Morristown, NJ 07962, Phone: (973) 455-2000, Fax: (973) 455-4807 1-800-328-5111
   • Honeywell product model numbers & instruction Manuals: see http://yourhome.honeywell.com/home/Applications/FindYourModelNumber.aspx
   • [6] White Rodgers Thermostats and HVAC controls,
     
     Homeowner information: http://www.emersonclimate.com/en-US/brands/white_rodgers/Pages/wr-homeowner-info.aspx
     
     Contractor information: http://www.emersonclimate.com/en-US/brands/white_rodgers/wr_contractor_info/Pages/white-rodgers-contractor-info.aspx
     
     White Rodgers Product Catalog (don't misspell the company's name as White Rogers Thermostats) -
     http://www.emersonclimate.com/Documents/thermostats.pdf - Thermostat Catalog
   • [7] White Rodgers 1F90 Low Voltage Digital Comfort-Set thermostat Installation Instructions, PN 37-3654, White-Rodgers Division, Emerson Electric Co., 9797 Reavis Rd., St. Louis MO 63123
   • [8] "Automatic Oil Burner Controls - Thermostats", Domestic and Commercial Oil Burners, 3rd Ed., Charles H. Burkhardt, McGraw Hill, 1969 (and later editions), ASIN B0000EG4Y8
   • [9] Thermostat wiring color codes & conventions, Thanks to reader " Helpful Pointers" Regarding 24V T, 10/7/2012
   • [10] Domestic Central Heating Wiring Systems and Controls, 2d Ed., Raymond Ward, Newnes, ISBN-10: 0750664363, ISBN-13: 978-0750664363, Quoting from Amazon.com:
     
   • [11] Proliphix Corporate Headquarters [Website: proliphix.com] , 3 LAN Drive Suite #100, Westford, MA 01886 Phone: +1.978.692.3375 Toll Free (U.S.): 866-IP-LIVING (866.475.4846) Fax: +1.978.692.3378 - Sales: sales@proliphix.com Marketing: marketing@proliphix.com Customer support: support@proliphix.com http://www.proliphix.com/ - quoting from the company's website:
     
   • [12] "Heating Control Handbook for the Installer and Service Man,Oil Burner, Gas Burner and Stoker Controls", Honeywell Corporation, March 1949 [copy on file as HoneywellControlsHandbookSA1399-2-1949.pdf] . Some of the controls discussed in detail here include the
     • Honeywell T1 and T11A = Series 10
     • Honeywell T21A (T2) = Series 20
     • Honeywell T847A = Series 80
     • Honeywell RA117A (RA1) = Series 10
     • Honeywell LA101A = Series 10,
     • Honeywell LA419A (LA4) = Series 40
     • V155A = Series 10, V435A = Series 40, V575A = Series 50, V835A = Series 80
   • [13] Trane TCONT800 Series Touch Screen Programmable Comfort Control Ownes Guide, American Standard, Inc., Troup Highway, Tyler TX 75711, January 2005, Telephone: Customer Service: 1-877-3381, website: www.trane.com
   • In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
     
     CONTINUE READING or RECOMMENDED ARTICLES.

   • Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
     
     Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The HOME REFERENCE BOOK - the Encyclopedia of Homes and to use illustrations from The ILLUSTRATED HOME .
     
     Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.

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