Guide to Installing & Wiring Heating, Heat Pump, or Air Conditioning Thermostats InspectAPedia® -
Guide to Thermostats for Heating and Air Conditioning Systems
How Do I Install & Wire Up a Room Thermostat like the Honeywell Round Wall Thermostat?
Questions & answers about heating, air conditioning, and heat pump thermostat installation and wiring
This article explains the basics of wiring connections at the thermostat for heating, heat pump, or air conditioning systems.
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This article is part of THERMOSTATS our article series Guide to Finding, Using, and Adjusting Thermostats for Heating & Air Conditioning Furnaces & Boilers, Heat Pumps or Electric Furnaces or Boilers. This website answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect
residential heating systems to inform home owners, buyers, and home inspectors of common heating system defects.
The articles at this website describe the basic components of a home heating system,
how to find the rated heating capacity of an heating system by examining various data tags and components, how to recognize common heating system operating or safety defects, and how to save money on home heating costs.
We include product safety recall and other heating system hazards.
2-Wire Thermostats: How Do I Install & Wire Up a Room Thermostat like the Honeywell Round Wall T87F Series Thermostat?
Our photo shows the backing plate that is mounted first when installing a round Honeywell type room thermostat. Notice that the plate shows a "level" line. We left off the actual wires so that you could see the "R" and "W" by the two screw terminals at the lower left 7 and 8 o'clock positions on the thermostat backing plate.
It's important to mount mercury-bulb thermostats as level as possible since otherwise you're putting the thermostat out of accurate temperature calibration.
That's because the coiled bimetallic spring has to move that mercury bulb to a tipped position to turn the heating or air conditioning system on or off in response to room temperature.
When we found a thermostat that did not heat a room accurately to the called-for temperature, we'd take a look to see if it was installed out of level before looking further.
Because the "set" range on these thermostats may have had a lower-end of 55 deg .F., when we wanted the thermostat to maintain a building at a temperature lower than the minimum that the thermostat dial provided, we just tilted the whole thermostat backing plate on the wall in the proper direction to shift the operating range of the switch.
Newer thermostats that rely on other sensor and switch designs may not have this sensitivity to being out of level.
Where Do We Connect the Red, White, & Blue (if present) Wires to a Typical Two Wire Wall Thermostat?
Watch out: do not short any wires together. Turn off power & confirm it is off. Don't forget to turn off all electrical power involved with your heating system before working on thermostat wiring, and confirm that power is off where you are working by using an appropriate test instrument such as a VOM. Failure to respect this advice risks equipment damage, and in some cases electrical shock or even a building fire.
Wiring connections for a room thermostat such as the Honeywell 24-volt T87F, the Honeywell series 10 (out of production), or Penn "Rimset" low-voltage wall thermostat models are pretty simple as are the wiring instructions for White Rogers, Mercoid, General Controls, and similar thermostats.
So what are the proper wiring connections for a room thermostat?
This little photo is included so that you can see that on many thermostats the wiring instructions are embossed right on the thermostat body. Look for them on your thermostat as well as reading them in the instructions that came with the thermostat. (You kept those, right?)
Two wire thermostat wiring instructions: In a two-wire installation, the thermostat backing plate is mounted level on an interior wall in the room which we want to be the master temperature control for the area served by the heating or cooling system.
The red wire from the heater or air conditioner control is mounted to the "R" terminal on the backing plate.
The white wire from the heater or air conditioner control is mounted to the "W" terminal on the thermostat mounting plate.
3-Wire Thermostats: Where Do We Connect the Red, White, & Blue (if present) Wires to a Typical Three-Wire Wall Thermostat?
Three-wire thermostat wiring instructions, also called "series 20 installations" we have three wires rather than two to connect.
The Red wire coming to the thermostat from the heater or air conditioner is connected to "R".
The white wire is connected to the "Y" terminal, and
The blue wire is connected to the "W" terminal on the backing plate.
Then the thermostat body is screwed in place. The screws that secure a round Honeywell traditional wall thermostat to its backing plate will also connect it properly to the wiring.
A plug connector may be used: On other thermostats it may be necessary to plug in a connector between the thermostat and its mounting plate.
6-Wire Thermostats: Where Do We Connect the Red, White, & Blue, Yellow, Green, Orange Wires in a Typical Six-Wire Wall Thermostat?
Color Codes and Hookups for Thermostat Wires, typical for heat pump installations and thermostats
Reader Bryan contributed this nice summary of what the various thermostat wires usually control, by color code:
The wiring to a thermostat unit depends on if you have
a heating system only
a heat pump, providing both heating and cooling
air conditioning unit only
Thermostat wiring also depends on how the installer has wired the thermostat.
Typical Thermostat Wire Connections for Heat Pumps
Typical connections when wiring a heat pump are as follows:
Typical thermostat connections when wiring a thermostat to control only a heating system or only an air conditioning system
If your thermostat is controlling only a heating system or only an air conditioning system, you will only have a red wire, and a white wire coming form the inside unit, to the outside unit.
On an air conditioner these two wires will go on the contactor to send 24 volts to the coil to pull the contactor in to start the air conditioner.
On a heating system these two wires will go to two thermostat connections on the primary controller such as an aquastat or air handler control that turns on the heating unit. Depending on the type of heating system, the thermostat, acting simply as an "on-off" switch will
- Hot water heat In the U.S. the TT wires will turn on a hot water circulator (or open a zone valve) on a hydronic or hot water heating system; falling boiler temperature will cause the aquastat to turn on the oil or gas burner (this is the U.S. typical installation).
- Hot water heat In Canada the TT wires will activate an aquastat control that will turn on and off the boiler based on its temperature; circulators are already running.
- Hot air heat: the TT wires will turn on the furnace heating equipment (oil or gas or electric, say); when the air temperature in the furnace heating plenum is hot enough the fan limit switch will turn on the blower fan.
These are the traditional wiring schematics, again, check the thermostat to see if this is the case with yours.
Instructions for Wiring of Line Voltage 120V Wall Thermostats
See this 1949 Honeywell Control Handbook for an explanation of older line voltage (120-Volt) and 24-Volt thermostats and other controls such as the T40 series 4-wire 120V T44 Thermostat
Shorting Out Thermostat Wires - Leads to Loss of Heat
Watch out: do not short any wires together. Turn off power & confirm it is off. Don't forget to turn off all electrical power involved with your heating system before working on thermostat wiring, and confirm that power is off where you are working by using an appropriate test instrument such as a VOM. Shorting thermostat wires to ground or together is likely to damage components in the thermostat itself or in other heating system components, as this reader's report below illustrates:
I had a no heat situation since replacing my programmable thermostat. I did some checks that the thermostat company said and the thermostat is good. But now my furnace won't come on at all. I can hear the transformer humming. It is a Miller model #M3RL-080-ABW in a four year old manufactured home.
Apparently I touched two live wires together when doing the thermostat installation. I know, I should have turned off the breaker, (power), before working. That is the lesson of the week for sure!
I blew a small purple, two prong, auto style fuse in the electrical board on my furnace. What I did not know is the fuse was marked with a "E" instead of a number, but it is a 4 amp fuse, found at your local automotive store. I was without heat all weekend, even though it could have been on Friday evening.
I'm glad I pulled the fuse and looked to see the metal inside was broken. Otherwise I might have been without heat until I could get a HVAC guy to come out to my house. -- S.R.
A Table of Common Heating and Cooling Thermostat Wiring Connections for Major HVAC & Thermostat Brands
The following thermostat wiring suggestions were derived from a thermostat wiring connection code list provided courtesy of J. Scott Meenan.
Watch out: do not short any wires together. Turn off power & confirm it is off. As we have warned before, don't forget to turn off all electrical power involved with your heating system before working on thermostat wiring, and confirm that power is off where you are working by using an appropriate test instrument such as a VOM. Failure to respect this advice risks equipment damage, and in some cases electrical shock or even a building fire.
Common HVAC Thermostat Wiring COnnections
Terminal Name
Nominal Wire "Color"1
Function
Generic HVAC thermostat control wiring points [see other brand specific notes below]
(B)
Blue, Orange
Energize to heat. Used on some systems including Rheem/Ruud HVAC systems. See (O) below.
(B)
Blue, brown , or black
Blue, brown , or black wire, common side of the transformer. Needed on some electronic thermostats or if the system uses indicator lamps.
Watch out: do not confuse this terminal with the (B) discussed above. Check you brand, model, and installation manual/wiring diagram.
(Also see (X) below)
(C)
Common side of the transformer (see "B")
(E)
Blue, Pink, Gray, or Tan
Blue, pink, gray, or tan wire, emergency heat relay on a heat pump. [Active all the time when selected, usually not used -??]
(G)
Green
Furnace blower fan (used in air conditioners, heat pumps, some electric furnaces.)
On most thermostats the (G) and (Y) terminals are connected together at all times when the fan switch is in the "Auto" mode.
(O)
Orange
Energize to cool, used for reversing valve on heat pump systems.
(R)
Red
Electrically live side ("hot" side) of the transformer wiring
(T)
Tan, Gray
Outdoor heat anticipator reset
(W) (W1) (W2)
White
"Heat", such as for a gas burner, oil burner, electric heat, or auxiliary heat on a heat pump, including the defrost output from an outdoor (condenser) that is used to activate electric heat at the compressor and to turn on the AUX heat lamp indicating that backup electric heat is in use or required.
Some heat pumps require a jumper from (W) to (Y) to operate the heat pump.;
(X)
Also see (B) above.
(Y)
Yellow
Compressor activity: cooling, or cooling and heating if on a heat pump
Thermostat Wiring Terminal Notes for typical
Two-Wire Flair 2-wire type Wall Thermostats (3 wires found at the wall thermostat)
Flair model ANOVO Thermostat fed from a Flair zone valve
(4)
As wire colors may vary, note the wire colors
Wire coming from Flair zone valve terminal (4) "Open"
(5)
at the zone valve.
Wire coming from Flair zone valve terminal (5) "Common"
Thermostat Wiring Terminal Notes for typical
Two-Wire Flair 3-wire type Wall Thermostats (3 wires found at the wall thermostat)
Flair model ANOVO Thermostat fed from a Flair zone valve
(4)
As wire colors may vary, note the wire colors
Wire coming from Flair zone valve terminal (4) "Open"
(5)
At the Flair zone valve and
Wire coming from Flair zone valve terminal (5) "Common"
(6)
Match those colors to terminals at the thermostat as shown here
Wire coming from Flair zone valve terminal (6) "Closed"
Thermostat Wiring Terminal Notes for typical
Two-Wire Honeywell T87-F type Wall Thermostats (only 2 wires found at the wall thermostat)
Honeywell thermostat T87F type models include the Super Tradeline T87F1959 (replaces the T26A1433 and T87C1252), T87F1867, T87F2816, T87F2824, T87F2873. These thermostat T87F models vary by the operating temperature range they support and a few other simple features such as the presence or absence of a thermometer. Functionally and for wiring they are similar.
(R)
Red
Red wire coming to the thermostat from the heater
(W)
White
White wire coming to the thermostat from the heater
Thermostat Wiring Terminal Notes for typical
Three-Wire Honeywell Wall T87-F type Thermostats (3 wires found at the wall thermostat)
(R)
Red
Red wire coming to the thermostat from the heater
(W)
Blue wire
Connect the blue wire coming to the thermostat from the heater or air conditioner
(Y)
White wire
Watch out: Connect the white wire coming to the thermostat from the heater or air conditioner to the (Y) terminal, not the (W) terminal.
Thermostat Wiring Terminal Notes for
General Electric (GE), Trane, American Standard HVAC
Numbers
Refer to the equipment wiring diagram (usually glued inside the equipment access covers and in the the installation/service manual). May be stages of electric heat, especially on
Air-Pro, Borg Warner, Coleman-Evcon, Frasier Johnson
(L)
Blue, Brown, Tan, or Gray
Service indicator lamp
(W2)
Pink or other color
Second stage of heat (may be same as (W) on heat pump or oil/gas systems.
(X2)
Second stage of electric heat on GE/Trane/American Standard systems. Also used as indicator lamp or misc. contact on other systems.
(Y2)
Blue, Pink
Compressor second stage
Thermostat Wiring Terminal Notes for
White Rodgers 1F90 Low Voltage Programmable Digital Comfort-Set
White Rodgers 1F90 Used For 2-wire Heating Only Systems
(W)
White
White wire coming to the thermostat from the heater or from the secondary (C) terminal on the transformer, routed through a White Rodgers isolation relay.
(RH)
Red
Red wire coming to the thermostat from transformer secondary (R) terminal. The same transformer (R) terminal typically also feeds a gas valve or vent damper, but not through the thermostat.
White Rodgers 1F90 Used For 3-Wire Series 10 Heating Systems
(W)
White
White wire coming to the thermostat from the heater
(RH)
Red
Red wire coming to the thermostat from the heater. From transformer secondary (R) terminal.
(B)
jumper wire
Add a jumper between (R) and (B) on the primary control
(R)
jumper wire
Add a jumper between (R) and (B) on the primary control
Notes:
1. Color: markings in the thermostat wall plate or in some models at other terminals on the thermostat body itself may indicate conventional wire colors that connect to this terminal, or the terminal ID with a letter such as "R" = red, as we illustrate above.
Watch out: the colors of the wires that you connect to these terminals do not necessarily match the nominal "terminal ID", as we illustrated above at "How Do I Install & Wire Up a Room Thermostat "
Lennox thermostat and equipment wiring color codes may vary significantly from common usage. Be sure to consult with Lennox and obtain the proper installation manual for your equipment.
These White Rodgers Tables Map Old Thermostat Wires to New (White Rodgers) Thermostat Terminals & Help Identify Old Thermostat Types
Thermostat Terminal Identification Table
Old Thermostat Terminal Marking or ID
Old Thermostat Type
4
W
RC
Y
G
1
RH
W
RC
Y
G
2
M
H
V
C
F
3
RS
4
Y6
G
4
R
W
Y
G
5
Source: White Rodgers 1F90 Low Voltage Digital Comfort Set Thermostat Installation Instructions
Map of Old Thermostat Terminals to New TT Terminals
Old Thermostat Type
New
Old
New
Old
New
Old
New
Old
New
Old
1
RH
4
W
W
RC
RC
Y
Y
G
G
2
RH
RH
W
W
RC
RC
Y
Y
G
G
3
RH
M
W
H
RC
V
Y
C
G
F
4
RH
R5
W
4
Y
Y6
G
G
5
RH
R
W
W
Y
Y
G
G
Source: White Rodgers 1F90 Low Voltage Digital Comfort Set Thermostat Installation Instructions
Questions & Answers regarding this article
Questions & answers about heating, air conditioning, and heat pump thermostat installation and wiring
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Thanks to reader S.R. for discussing loss of heat due to a thermostat wiring mistake, October 2010
Thank to Mr. Scott Meenen, G&S Mechanical Services, for providing some common thermostat wiring codes also found at Mr. Meenen's web page http://toad.net/~jsmeenen/wiring.html . 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 jsmeenen@toad.net - 10/2010. Quoting:
We service American Standard, Amana, Arco, Arco-Air, Bryant, Carrier, Coleman Evcon, Comfortmaker, Day/Night/Payne, Dunham-Bush, Fedders, Fredrich, Goodman, General Electric, Heil, Intertherm, ICP, Janitrol, Lennox (Armstrong, Johnson Air-Ease), Miller, Modine, Nordyne, Rheem/Ruud/Weatherking, Sears, Stewart Warner, Trane, Weather King, Williams, White-Westinghouse, Whirlpool, Weil Mclain, York, (Frasier Johnson/Borg Warner) and others.
Domestic Central Heating Wiring Systems and Controls, 2d Ed., Raymond Ward, Newnes, ISBN-10: 0750664363, ISBN-13: 978-0750664363, Quoting from Amazon.com:
This unique A-Z guide to central heating wiring systems provides a comprehensive reference manual for hundreds of items of heating and control equipment, making it an indispensable handbook for electricians and installers across the country. The book provides comprehensive coverage of wiring and technical specifications, and now includes increased coverage of combination boilers, recently developed control features and SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) boilers ratings, where known.
In addition to providing concise details of nearly 500 different boilers fuelled by electric, gas, oil and solid fuel, and over 400 programmers and time switches, this invaluable resource also features numerous easy-to-understand wiring diagrams with notes on all definitive systems. Brief component descriptions are provided, along with updated contact and website details for most major manufacturers.
"Automatic Oil Burner Controls - Thermostats", Domestic and Commercial Oil Burners, 3rd Ed., Charles H. Burkhardt, McGraw Hill, 1969 (and later editions), ASIN B0000EG4Y8
Proliphix Corporate Headquarters,
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: All Proliphix Network Thermostats come with our free Uniphy Remote Management Service. This unique offering lets you monitor and control your HVAC systems by simply pointing your Browser to our secure Proliphix Web Site. Enjoy the convenience of programming a thermostat from any location, using a simple graphical interface. No computer equipment or software is required. And since Proliphix takes care of the network configuration for you, you’ll be up and running in no time. We’ll even proactively monitor your thermostats and send you an immediate email or SMS message when an HVAC problem is detected.
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
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
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
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
Links to our list of additional information on heating system inspection, repair, maintenance
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