Thermostat wiring details & connections for nearly all types of Resideo or Honeywell room thermostats used to control residential heating or air conditioning systems.

This article gives a table showing the proper wire connections for Honeywell brand wall or room thermostats used to control heating or air conditioning equipment.

Room thermostat installation & wiring guide: this article series explains the basics of wiring connections at the thermostat for heating, heat pump, or air conditioning systems.

Our page top sketch, courtesy of Honeywell Controls, illustrates the wiring diagram for a traditional Honeywell T87F thermostat used for 2-wire single pole single throw control of heating only in a typical gas-fired heating system.

Resideo - Honeywell Thermostat Wiring Guide

These questions and and answers about how to hook up or wire various models of Honeywell heating & cooling thermostats were posted originally

at THERMOSTAT WIRING HONEYWELL - be sure to see the wiring diagrams and procedures given there or in the detailed thermostat wiring procedures linked-to just below.

Note: In 2018 Honeywell announced that Resideo would be the corporate name of the Honeywell Homes product portfolio and ADI global distribution businesses.

Honeywell T87 type thermostats, wiring connections, instructions, diagrams

• THERMOSTAT WIRE CONNECTIONS - topic home, all brands
• HONEYWELL SERIES 20 WALL THERMOSTAT WIRING - home
• HONEYWELL 5-2 DAY PROGRAMMABLE THERMOSTAT - RTH2300B1012 WIRING
• HONEYWELL T87-F type 2-WIRE WALL THERMOSTAT WIRING
• HONEYWELL T87-F type 3-WIRE WALL THERMOSTAT WIRING
• HONEYWELL T87 WALL THERMOSTAT WIRING DIAGRAMS, OTHER - Honeywell Wall T87-F type Thermostats for sketches and drawings of Honeywell thermostat wiring hookups.

On 2020-12-03 - by (mod) -

I'm baffled, too Jerry. I would suspect a problem not with the thermostat or its wiring but with the controls at the heater itself, perhaps getting in trouble when at lower temperatures the burner (is this oil or gas?) runs longer at a time, maybe overheating a control. I'd call for help from a service tech and I hope you'll let me know what she finds.

On 2020-12-02 by jerry and Brenda Slayton

we have the rth2300/rth221,with red,white,black wires.heat is hot water baseboard.works ok in daytime but at night goes down to 50 degrees even set to 62 degrees.why?
email=shamrock17@vermontel.net
thank you.

On 2020-11-15 - by (mod) -

Sure, Jackie. Cap off any unused wires.

On 2020-11-10 by Jackie Jackson

Can i hook up a honeywell ct31a without connecting the yellow wire since my ac is disconnected?

On 2019-10-28 - by (mod) -

Can you clarify what temperatures don't match?

Keep in mind that the room temperature that your thermostat senses and reports is affected by its location, drafts, sun, heat or air movement in the wall cavity, etc. so if you measure room temperature elsewhere you'll pretty much always get a different temperature.

On 2019-10-24 by Pst

I replaced an old honeywell non digital with a new ome same model .temperatures dont match. Is there an adjustment on the temp set

On 2018-12-30 - by (mod) -

Glad to help, Dee.

See the diagnostic suggestions at

FURNACE FAN CYCLES DURING HEAT https://inspectapedia.com/heat/Furnace_Fan_Cycles_During_Heat.php

there we discuss the common causes of a blower fan cycling on and off as you describe.

On 2018-12-30 by dee

the heater comes on and runs for 5 min then off for 5 min and comes on again

On 2018-11-18 by (mod) - cap off un-used thermostat wires

No, Ian.
Just cap off the unused wire.

On 2018-11-16 by Ian

Forgot to mention it's a non programmable thermostat RTH5160

I have a 3 wire boiler heat system Red,White, Green but was only using red,and White I bought the honeywell RTH5160 Series do I need connect the Green wire

On 2018-11-15 by (mod) -

Delroy

Check to see if you've reverse the heating and cooling wires in the thermostat connections

On 2018-11-14 by Delroy

Have a central a\c thermostat is bad change it out but blowing hot air when it's on cold

On 2018-10-07 by (mod) -

DC

Here is a copy of the HONEYWELL RTH2300/RTH221 SERIES PROGRAMMABLE THERMOSTAT OWNERS MANUAL [PDF]

https://inspectapedia.com/heat/Honeywell-RTH-2300-Thermostat-Manual.pdf

that will review the role of each connector.

Compare those connections with the wiring instructions for your Blaze King gas fireplace

You didn't say which Blaze King you have, so you will want to go here http://www.blazeking.com/EN/gas-manual.html to find the right manual for your gas fireplace.

Without those details any further wiring guesses on my part - knowing not what you have installed - could be too dangerous to offer.

On 2018-10-07 by dcif

My Honeywell rth230b is wired with the red and yellow both in the RH slot and a black and green wire both going to the W. this is for a Blaze King gas fireplace...any ideas on how to wire it with a Honeywell RTH7500?

On 2018-10-07 by (mod) - recommended non-programmable replacement for Honeywell RTH2300B

Ray

Check out the T8775C1005 from Honeywell, shown below. This is the company's replacement for the traditional T87 round, non-programmable thermostat.

On 2018-10-06 by ray

Can you recommend a non-programmable replacement for a Honeywell RTH2300B/1038. Thanks

On 2018-08-15 by (mod) -

Larry the fan is controlled by a relay and control board in the compressor unit, not your indoor wall thermostat.

But if the outdoor compressor/condenser unit doesn't run at all, the problem could be a mis-wired thermostat.

On 2018-08-10 by larry

installed Honeywell CT87n thermostat replacing a digital thermostat; the a/c compressor runs and cools, but, the a/c compressor fan is not running

On 2018-08-08 by (mod) -

Den

Go to your air conditioner or heater, see where the blue and brown wires are connected. If there are just two wires used, it may be that the service tech simply used those colors instead of the standard red and white.

Don't connect anything until you know what the wires do or did previously.

On 2018-08-08 by Den

Yes i have s rth2300 termostat not sure how to wire it i have a blue wire and a brwn one that doesnt explain in the directions please help

On 2017-10-22 by (mod) -

Don,

Thank you for taking the time to make that comment, I will review the article and material to make sure that the very basic wiring that you described as made clear.

I know we've discussed it elsewhere in this series, but it should have been easier to find.

On 2017-10-21 by Don Walden

No Instruction on the RTH2300?RTH221 about a two wire system, finaly figured it out use R W connection be nice if i could have found it

On 2017-10-16 by David

Replacimg a programmable thermostat with a manual Honeywell. Basic Bryant electric furnace that just has a convential a/c unit (but this furnace can also be configured for a heat pump). So ... 5 standard wires - R Y G W and B. Hooked up wires to corresponding posts on new tstat R-R, W-W, Y-Y, G-G, B-B.

Set dip switches per Honeywell instructions. At first a/c came on fine. Turned to heat - nothing. Fan wouldn't come on set it to manual and no heat.

Must add that was holding conversation with home owner when I removed old stat so NOT sure where blue wire was connected (while looking at online instruction I see blue wire is mainly not connected to blue post.
WTH did I do wrong.

On 2017-06-18 by Eddie m.

My central air turns on and off for days but suddenly the outside unit will not come on. If I turn the system off for 6or8 hours everything works fine for awhile,help

On 2017-06-09 by (mod) -

Typically, Isaac you'll buy a 4-wire thermostat, then don't make use of a 4th wire connection as it's for a feature that your HVAC system doesn't use. Or there may be instructions with the thermostat to use a jumper between two terminals.

On 2017-06-09 by Isaac

I'm putting in a new thermostat for baseboard heat and my old one is 3 wires. I can only find a 4 wire or 2 wire thermostat. How am I suppose to wire it?

On 2017-03-14 by (mod) -

Anon
the rth6350d1000 -1027 you cite, I assume, refers to a Honeywell 5-2 Day Programmable Thermostat (RTH6350D) - so I'm unsure what you're asking. That thermostat is designed to control both heating and cooling systems, so a heat pump should be no trouble.
If you don't have the manual see http://yourhome.honeywell.com/en/products/thermostat/5-2-day-programmable-thermostat-rth6350d

On 2017-03-14 by Anonymous

I have a rth6350d1000 -1027
I have a heat pump
What thermostat is compatible?

On 2017-01-17 by Bobbie

Forgot to tell you when the previous comment it's just for an oil heat hot air blower

I'm replacing an Old Mercury thermostat to a digital one that's simple is two white wires coming out of the wall and a black one where do I put them

On 2016-07-09 by keith

I have a ct87n honeywell thermostat,5-wire,Where does the blue wire go?

On 2016-07-09 by Terry

I have a honeywell mercury basic 2 wire heat only thermostat, I bought a Honeywell RTH111B Heat/cool thermostat, Can I hook this up using one side or the other, Heat only or cool only being that I only have 2 wires?

On 2016-06-03 by Anonymous

I have a class2 lr95329 thermostat
Will that run heat and air with just 2 wires. The heat will kick in and out but the air is not.

On 2016-01-05 by (mod) -

Wendy,

The function of option switches on a thermostat depend on the brand and model. An example: some thermostats allow the installer to specify the type of heat the thermostat is controlling by fuel (oil, gas, electric) or by heat delivery (forced warm air, forced hot water) and the thermostat may then adjust its heat anticipator or other features to work best with that system.

On 2016-01-05 by wendy

in my thermostat there are 3 switches labeled 1-3 says option switches what are they for?

On 2015-12-05 by (mod) - converting a 6-wire to a 4 wire thermostat

Shane:

The thermostat installation guide for the Honeywell CT31A series instructs us to identify the functions of each of the original wires and to label them according to the terminal ID's to which each was connected in the old thermostat.

Next if the new thermostat is a model that supports all of the features of the old one the instructions include a terminal map. If you don't have that data let me know and I'll help you obtain the instructions from Honeywell.

Existing wires Connect to:

R • RH • 4 • V Terminal “R”

W • W1 • H Terminal “W”

Y • Y1 • M Stop! See note

G • F Stop! See note

Rc Stop! See note

WATCH OUT: regarding the "note" - If any of these wires are present, you cannot use this Honeywell ct31a1003 thermostat with your system.

On 2015-12-05 by shane

I have an RV and the original wiring is 6 wires for gas heat and electric ac.

I now have a new thermostat Honeywell ct31a1003 and is a 4 wires. How can I wire the thermostat to work the heat I have two wires that I need but nowhere to wire it. Help

On 2015-11-02 by (mod) -

Glenn,

I took a look at the Honeywell RTH8500WF owners's guide that includes installation procedures. It looks pretty easy. On the new thermostat (the RTH8500WF) you'll see terminals marked RC (red-common) and W (white) to which you'll connect the wires. Be sure to read and follow all of the instructions including some good suggestions about labeling wires and of course turning off power to the system while fooling around with the thermostats.

Use our page bottom CONTACT link to send me photos of your old and new thermostats, wires, and any questions that arise may be more easily addressed.

On 2015-11-02 by Glenn

I have a 2 wire Honeywell ct87k thermostat and want to replace it with a Honeywell wifi thermostat RTH8500WF, can this be done? if so, how do I connect the two (R & W) wires?

On 2015-04-11 by Steve

I have a Honeywell with three wires connecting to the terminator labeled, Data, R, C. It does provide both heating and cooling and I am trying to connect an Ecobee and have to map those wires to the normal Rc, Rh, C, G, W, Y1, Y2. Any idea how I would do that?

Question: Replacing a round Honeywell T87 with a Digital Honeywell Thermostat

Hello - I am replacing a round Honeywell T87 thermostat (shown above) with a non-programmable digital Honeywell unit (shown below). I have a hot water system with multiple zones and with no air conditioning.

There are three wires at the thermostat. On the old round unit the red wire went to the R terminal, the white wire went to the w terminal and a green wire went to B terminal. I hooked up the new stat the same way but it would not work

If I selected "fan on" instead of "fan auto" the zone would heat up but would not shut off (hot water kept flowing even if I selected a temp below room temp). Appreciate your help. - Patrick - 1/20/12

Reply:

Patrick, typically the three wire thermostat hookups would be exactly the same for the old and new thermostats.

For details of wiring a typical and simple digital Honeywell thermostat, see Honeywell 5-2 Day Programmable Thermostat - RTH2300B1012.

For help in understanding the wiring of your old thermostat, see Three-Wire Honeywell Wall T87-F type Thermostat wiring and also see Generic HVAC Thermostat Control Wiring Points

Question: Replacing a mercury thermostat with a digital unit

I am replacing an old mercury thermostat with a digital. my system is a heat pump. my neighbor gave me the digital, no instructions, no box.

i'm trying to decide if this is even a heat pump compatible thermostat. on the therm it has c, g, rc, rh (which are linked by a black wire.) w, y, b, and o. coming out of my wall is, white connected on old therm w2, yellow connected to y, green conn g, black conn e, red to r, blue to b and bro to x. any help would be great. - Kurt 6/4/12

Reply:

Kurt, as you see in the examples at For help in understanding the wiring of your old thermostat,

see Three-Wire Honeywell Wall T87-F type Thermostat wiring and also see Generic HVAC Thermostat Control Wiring Points.

Many thermostat wiring setups are straightforward or "cookbook" but why not find the brand name on your thermostat and then you can obtain the installation instructions right from the manufacturer?

Also, Honeywell's thermostat replacement advice (and most likely that of all thermostat manufacturers) warns:

Watch out: MERCURY NOTICE: Do not put your old thermostat in the trash if it contains mercury in a sealed tube. Contact your local waste management authority for instructions regarding recycling and proper disposal.[5]

Question: where does the "W" wire go on a new thermostat without a "W" Terminal?

(June 11, 2014) I have a white wire but the new thermostat doesn't have a W terminal said:

My old thermostat has this:
R, G, Y, O/B (orange wire), W, C (blue wire)

New thermostat has this:
R, G, Y, O, B, C, and "not used"

I assume the orange wire goes to "O", but where does the white wire from "W" go?

Reply:

Place a jumper (piece of wire) between Y and W if you have a heat pump without auxiliary/back-up heat.

Question:

Aug 18, 2014) Robert said:

Trying to replace a Honeywell model T834C1954 mercury stat (for heat pump) with new Honeywell programmable.

Old stat has YELLOW wire going to terminal marked "P" - new Honeywell stats have no "p" terminals.

Honeywell "tech" line person could not help - said I would have to trace yellow wire back to the pump - easier said than done. Any thoughts what terminal on new stat would be compatible with old "P" terminal?

Reply:

Robert, I can't know what your system's yellow wire is doing, but by generic color code convention

(see inspectapedia.com/heat/Thermostat-Wire-Color-Codes.php )

Yellow is for the switched compressor compressor control circuit - for air conditioning or a heat pump.

(Aug 21, 2014) Robert said:
Dan Joe, thank you!!! Based on your response, then, I "should" be safe in connecting this yellow wire to the "Y" terminal in the new programmable stat?

Presuming "worst case" scenario to be heat pump would simply not work properly and I just live with old stat? It is curious, tho, that old stat has a dedicated P terminal and none of new ones do.

Appreciated your quick response - thanks again1
Robert

Reply:

Robert, I'm naturally scared to say "safe" for anything diagnosed only by e-text, but I've indicated what we know about wiring *conventions* - nobody here knows what actual wiring connections have been made at your home.

You could try tracking down what wires go where by finding what you think is the other end of the same colored wire and using a VOM to confirm or test for continuity.

(Aug 21, 2014) Robert said:

Absolutely understand and would never expect you to sign off on an e-text situation. As for tracking down the wiring to the source, this will be difficult.

The "home" is actually an apartment unit in a high rise building that my daughter just moved to. The "mechanical" room for the heat pump is basically a broom closet and, without knowing directly for what I'm looking . . . well, you can probably understand.

Your "tracking down" suggestion is exactly what the Honeywell "help desk" finally offered when I called.

Thinking that we may just abandon the project, return the new stat, and daughter will get used to old fashioned manual heat/cool control.

Thanks again - I am impressed with your quick replies and effort to give advice.

Robert

Reply:

I'd regret giving up if in fact we could ultimately learn that the wiring solution was trivial.

Look in the broom closet foe an access cover on the air handler that can be removed. Turn off power to the unit. Look inside for the thin low voltage wiring, see if you see a yellow wire.

(Aug 22, 2014) Robert said:

Super! I will for sure give that a shot next time I am at the broom closet venue. We live 2 hrs. apart so don't have prompt access to the challenge. This really "should" be a simple thing, methinks. Appreciate your tenacity in sticking with me on this!! It may be a few weeks before I get to daughter and then back on this thread to give you an update.

But, stay tuned . . . "I'll be back!" =[:-)

Question: Siemens RAA20

(Oct 20, 2014) Blaine said:
Have a Siemens RAA20 (high rise hot water heat) with 2 black and 2 white wires. One black goes to connection L, one white to connection Y.

Other black and white wire are twisted together in a copper wire connection.

New thermostat Honeywell RTH2510B has the same Y connection but no L. It has O/B, RC, R, G, W/AUX.

I think the black wire connected to "L" in the Siemens RAA20 goes to terminal "G" on the new Honeywell, but not sure?

Any tips appreciated.

(Feb 24, 2015) Karen said:
Cannot get the red wire into "R" with a jumper wire in my new Honeywell RTH221. The old thermostat had the red wire in "RH" with a jumper wire.

...

Continue reading at THERMOSTAT WIRING HONEYWELL - how to wire a Honeywell room thermostat, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Thermostat Wiring & Installation Articles

• THERMOSTAT INSTALLATION STEPS - how to replace or install a new thermostat
• THERMOSTAT WIRING COLOR CODES & methods for identifying which thermostat wire is which if yours have lost their labels or have unclear color codes.
• THERMOSTAT WIRE CONNECTIONS detailed room thermostat installation & wiring guide for each heating or cooling system type and each thermostat brand / model
  • COMMON WIRE at THERMOSTATS
  • CONVERT LINE to LOW VOLTAGE THERMOSTAT
  • 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 B
• THERMOSTAT WIRING OPENING SEAL
• THERMOSTAT WIRING in PARALLEL / MULTIPLES
• THERMOSTAT WIRE TERMINAL ID CODES / FUNCTIONS - what are the R, W, and other thermostat wire terminals used for?

Suggested citation for this web page

THERMOSTAT WIRING HONEYWELL FAQs 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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