Installing NEST Thermostat - two wires

[Ian]

I am installing a new NEST thermostat, replacing an old two wire mercury bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.

Can anyone tell me which letters on the NEST base (W, Y, O/B, AUX, E, G, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.

Thanks,

Ian

[Nate Nagel]

http://www.behvac.com/troubleshooter41.htm

You'll probably need to repull the thermostat wire with at least three
wires so you have a common available to power the thermostat; I would
repull with 5 conductor in case you think you may want to add central
air in the future.

In short, one of the existing wires connects to "R" (if you have "RH"
and "RC" then connect to "RH") use "RED" wire for this connection. This
one will be the one coming directly from the transformer.

The other existing connection connects to "W" - use the "WHITE" wire for
this one.

Finally you will need another conductor from the 24VAC side of the
transformer to the new thermostat, that will connect to "C" for Common
and if there is a black wire in your cable use that one.

It says here that you "may" not need to repull if you don't have a "C" wire

https://nest.com/thermostat/installation/

Looking at the picture there, it appears the terminals you would use are
RH, W1, and C.

here's more info on why you may want to repull

http://support.nest.com/certified/article/Help-with-installation-and-set-up#common

Hope this helps

nate


--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

[Nate Nagel]

Forgot to add; if you repull then you can also use the fan-only mode.
Use the green wire for that function.

[Tony Hwang]

Hmm,
Why are you asking? Read the manual? No? You can download it.
Still have questions? Then ask.
2 wires? Where is another one for fan control? Maybe you are
future proofing but in this case NEST is way more than what you need.

[Tony Hwang]

Hi,
Why the trouble repulling wires? Some times it is almost impossible
pulling extra wires. In that case go wireless.

[k...@attt.bizz]

On Sat, 14 Dec 2013 07:52:40 -0800 (PST), Ian <ians...@stocknet.ca>
wrote:

>I am installing a new NEST thermostat, replacing an old two wire mercury bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.
>
>Can anyone tell me which letters on the NEST base (W, Y, O/B, AUX, E, G, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.

I don't believe a Nest will work on your system. Did you do fill out
their compatibility form?

[Nate Nagel]

In my last house it took longer to puzzle out the proper connections
within the furnace than it did to pull the thermostat wire. Open
ceiling in basement, and thermostat wire was clearly visible going
through floor, only had to do about 4 feet "blind." If that's the OP's
situation there's really no reason not to do it.

Obviously if it's a complete PITA to do so another solution might be
preferable.

[tra...@optonline.net]

What does the Nest install instructions say? Don't they tell you
how to hook it up to the most basic two wire install? Normally,
comming from furnace, connecting red to white would control it.
Does the Next have batteries and need no additional power or does
it need an additional common line back to the furnace?

[NotMe]

"Ian" <ians...@stocknet.ca> wrote in message
news:431b3a66-31cf-4c06...@googlegroups.com...

I've been fighting that battle for months. Thankfully I took still photo
before starting and set up a video camera to record the actual steps in the
process.

Nest is still not working but at least I could go back to where I started so
we have heat.

[Tony Hwang]

Hi,
Oh, my, if you read installation instructions and have difficulty
understanding what it says, wouldn't it be time for help from pro?
While it is being installed, you watch him and learn for next time. Or
Nest customer support no good? Or may I ask what seems to be issue to
complete installation?

[Stormin Mormon]

On 12/14/2013 10:52 AM, Ian wrote:

You'll have to read the furnished manual
(RTFM). We can tell you the traditional
color code, but yours might be different.

--
.
Christopher A. Young
Learn about Jesus
www.lds.org
.

[Irreverent Maximus]

"Stormin Mormon" <cayo...@hotmail.com> wrote in message news:%M3ru.2891$oo4...@fx02.iad...

OMG!

Verify that you have the battery powered Nest. If not, exchange the one you have for
a battery powered unit.

Turn off power.

Make note of current terminations to old thermostat and use provided wire markers
to make the proper designations. The old terminals will have markings that should
at least have an R and W on them. If not, no big deal.

Remove old thermostat base and install Nest base, make sure that it is level.

Connect to terminals W1 and RH of the Nest. It is preferable that you match the R and W, but
in a two wire system this really does not matter.

Put Nest thermostat on Nest base.

Program the Nest.

Turn power back on and operate the Nest.

Everything should work. If not, turn power off, reverse wiring and turn power back on. I
seriously doubt the Nest gives a rip about polarity. This should not be necessary.

To test the wiring (function of furnace), disconnect power. spin wires together.
Turn power back on. The furnace should fire up. If it does the Nest is bad, if not, then
you have a different issue.

[EXT]

"Tony Hwang" <drag...@shaw.ca> wrote in message
news:_m2ru.137884$r73.1...@fx23.iad...

I had a simple question, emailed customer service and got an answer back
right away.

Nest may be over kill for your needs, it can handle 2 stage heating, 2 stage
cooling, fan control, and via wifi it can be controlled by your computer,
smart phone or tablet, and firmware be automatically updated. If you cannot
use these features, it seems to be a waste to use on a 2 wire simple heater.

[Daring Dufas : Hypocrite TeaBillie on welfare]

It doesn't come with directions?

[Ian]

On Saturday, December 14, 2013 10:52:40 AM UTC-5, Ian wrote:

Yes, it comes with installation instructions, and I have read them, but there is no reference to a simple two wire (unmarked) set up.

And, yes, I know the nest has the capability to control much more than I have, but I want the ability to program, and control remotely. It's only marginally more expensive than the basic ones that provide that functionality.

In the end, I believe the answer is to connect the wires to Rh and W1.

Thanks,

Ian

[The Daring Dufas]

On 12/14/2013 3:49 PM, Daring Dufas : A Sock Of Killer Loon wrote:
> It doesn't come with directions?
>

Killer Loon, living proof that human females should never have sex with
farm animals. ^_^

TDD

[Tony Hwang]

Hi,
Yes, indeed but you have to connect right wire to the corresponding
terminal. W1 means 1 stage heat, RH means 24V AC control power lead, H
meaning for heating. If you cross this wires you may damage the 'stat.
Take a look at the furnace end to see if you can sort out this two
wires. If you measure the voltage between furnace frame and this wire,
one showing 24V AC or so is one for Rh terminal, the other one is for
W1. Some times wires are color coded.

[Oren]

On Sat, 14 Dec 2013 10:43:44 -0700, Tony Hwang <drag...@shaw.ca>
wrote:

>Why are you asking? Read the manual? No? You can download it.
>Still have questions? Then ask.

Husband and wife argue over the town name on a map.

Stop for fast food traveling in Florida. Husband asked the cashier; is
this Kimminee or "kiss-a-me".

Cashier states: No sir, this is McDonald's.

[Irreverent Maximus]

"Tony Hwang" <drag...@shaw.ca> wrote in message news:_k6ru.30450$dB7....@fx17.iad...

,
> Yes, indeed but you have to connect right wire to the corresponding
> terminal. W1 means 1 stage heat, RH means 24V AC control power lead, H
> meaning for heating. If you cross this wires you may damage the 'stat.
> Take a look at the furnace end to see if you can sort out this two
> wires. If you measure the voltage between furnace frame and this wire,
> one showing 24V AC or so is one for Rh terminal, the other one is for
> W1. Some times wires are color coded.

The instructions state that RH and W1 are the terminals to use. Even
if the "contacts" are solid state, mixing the wires would not hurt
anything.

[Tony Hwang]

Hmm,
Note the word "may". Until tried result unknown.

[N8N]

just try it, I doubt you will damage anything if it doesn't work.

make sure RH is connected directly to transformer

I suspect if you have any issues repulling to add a common will fix.

[Nate Nagel]

It might not recharge unless the "line" is correctly connected to RH.
Otherwise, I agree.

[mina...@gmail.com]

I just installed 2 of these nest thermostat in my house. Both 2 wire connection, un marked, The system is gas, radiant in floor heating and basically if you touch the 2 wires it completes the circuit and you have heat. My nest has a built in battery so it works even when i pull it off the wall. anyways you just need to connect W1 and RH and you are good to go, even if you get the wires backwards it will still work, i am not sure on if it will charge the nest if it is backwards. I am going to take a look at my relay box tomorrow and verify the color codes. i have both of the wired opposite so i know they work no matter what.

good luck.

[Tony Hwang]

Hi,
Nest 'stat has firmware bug, never heard about it? Off topic their
smoke detectors are being recalled.

[trader_4]

It apparently has a lot more serious problems. The long list of pissed
off customer complaints at Amazon is amazing. Last time I looked, which
was months ago, most of the complaints were related to using it in the
2 wire mode, where they try to rob power from the system to power the
thermostat. In order to reduce power to make that possible, instead of
using small relays like most other thermostats, they used FETs which
apparently burn out, don't work, etc. One feature they appear to have
that you gotta love is that it can and will install software updates
any time it wants to and you have no control over if it does, nor when.
Just what you want in a mission critical app. IMO this thing is great
if you want a stylish ornament for your wall. If you want a real thermostat,
that works, I'd get a Honeywell VisionPro.

[Tony Hwang]

Hi,
I maybe biased as Honeywell retiree, I like Honeywell Vision Pro line my
self. Just good for the guy who sold the Nest to Google for 3 billion.
Rule is the more a device gets fancy, the more possibility of some thing
behaving weird unexpectedly.

[sam E]

On 04/06/2014 12:31 AM, mina...@gmail.com wrote:
> I just installed 2 of these nest thermostat in my house. Both 2 wire connection, un marked, The system is gas,
> radiant in floor heating and basically if you touch the 2 wires it completes the circuit and you have heat. My
> nest has a built in battery so it works even when i pull it off the wall. anyways you just need to connect W1
> and RH and you are good to go, even if you get the wires backwards it will still work, i am not sure on if it
> will charge the nest if it is backwards. I am going to take a look at my relay box tomorrow and verify the
> color codes. i have both of the wired opposite so i know they work no matter what.

If it charges one way it should charge the other. This is 24V AC so
polarity doesn't matter. Phase doesn't matter either since there's
nothing to compare it to.

> good luck.
>

[kencarte...@gmail.com]

On Saturday, December 14, 2013 at 7:52:40 AM UTC-8, Ian wrote:
> I am installing a new NEST thermostat, replacing an old two wire mercury bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.
>
> Can anyone tell me which letters on the NEST base (W, Y, O/B, AUX, E, G, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.
>
> Thanks,
>
> Ian

I am considering buying a NEST thermostat today. I have one of the basic two wire thermostats where I have a white and a red wire. It's the type with the mercury bulb.

The guy came around from the installers and tried installing a nest three months ago and told me it would not work on a two wire system. I have heard different stories about this. Some say yes it does work, other say it won't work without pulling through a common wire (whatever that is, I am no electrician) My two wires are red and white BUT I also have two other wires that are there, a black and a green one that weren't connected at the thermostat. I am wondering if I could use one of those wires as a common if need be. I would imagine they are for a future install of a heat pump.

Can anyone advise me on this?.

Thank you.

[trader_4]

Assuming those additional wires run all the way back to the furnace,
which is likely, then yes one of them could be used as a common to
supply power. If the installer was at all competent, he should have
been able to deal with that the first time around.


I looked into the Nest a few years ago and from what
I saw, there were a huge number of problems, with most of them involving
trying to steal power with 2 wire installations. Things like it
shorting out, forcing the heat or cooling to full on, regardless of temp.

I think the Nest sucks for other reasons too. Lots of stories of
people saying that they can't control it, it just does what it wants,
etc. That's how it's marketed, isn't it? I saw people complaining
that if they were home from work, sick in bed, and wanted it to just keep
a set temp, it would just keep reverting back to figuring out that because
it didn't see movement for awhile, it thought you'd left the house.....
I don't need that. For me a Honeywell VisionPro that's programmable
works just fine. I would get internet connectivity in my next one,
so that I could control the heat from my phone, turn it up when I get
back to the airport, etc. Could get a VP that does that for $150.

Also, don't be fooled into some incredible claimed energy savings.
Those savings are mostly due to what you can do with any programmable
thermostat.

[micky]

In alt.home.repair, on Mon, 10 Aug 2015 08:19:51 -0700 (PDT), trader_4

<tra...@optonline.net> wrote:

>On Monday, August 10, 2015 at 11:11:45 AM UTC-4, kencarte...@gmail.com wrote:
>> I am considering buying a NEST thermostat today. I have one of the basic two wire thermostats where I have a white and a red wire. It's the type with the mercury bulb.
>>
>> The guy came around from the installers and tried installing a nest three months ago and told me it would not work on a two wire system. I have heard different stories about this. Some say yes it does work, other say it won't work without pulling through a common wire (whatever that is, I am no electrician) My two wires are red and white BUT I also have two other wires that are there, a black and a green one that weren't connected at the thermostat. I am wondering if I could use one of those wires as a common if need be. I would imagine they are for a future install of a heat pump.
>>
>> Can anyone advise me on this?.
>>
>> Thank you.
>>
>

>Assuming those additional wires run all the way back to the furnace,
>which is likely, then yes one of them could be used as a common to
>supply power. If the installer was at all competent, he should have
>been able to deal with that the first time around.
>
>
>I looked into the Nest a few years ago and from what
>I saw, there were a huge number of problems, with most of them involving
>trying to steal power with 2 wire installations. Things like it
>shorting out, forcing the heat or cooling to full on, regardless of temp.
>
>I think the Nest sucks for other reasons too. Lots of stories of
>people saying that they can't control it, it just does what it wants,
>etc. That's how it's marketed, isn't it? I saw people complaining
>that if they were home from work, sick in bed, and wanted it to just keep
>a set temp, it would just keep reverting back to figuring out that because
>it didn't see movement for awhile, it thought you'd left the house.....

This is the wave of the future. If you're just going to lie in bed for
hours, you should have gone to a hotel.

>I don't need that.

Of course you don't NEED it but it's modern, high-tech, and it's what we
will all have soon.

> For me a Honeywell VisionPro that's programmable
>works just fine. I would get internet connectivity in my next one,
>so that I could control the heat from my phone, turn it up when I get
>back to the airport, etc. Could get a VP that does that for $150.

There's something about coming into a cold house that seems like part of
taking a trip. It doesn't take long to warm up.

>
>Also, don't be fooled into some incredible claimed energy savings.
>Those savings are mostly due to what you can do with any programmable
>thermostat.

I'm sure you're right.

[Tony Hwang]

I strongly suggest you buy something else. Version 1 had big issues with
under-rated relay causing a/c compressor burn out when relay sticks.
There are many other choices like Ecobee, 3M, Honeywell, etc. They are
all WiFi thermostats. I believe 3M one is made by Honeywell.

[Tony Hwang]

BTW, I have wireless(no wires betweeen thermostat and system) and WiFi
Honeywell thermostat. I can control it any where in the world using
internet. using computer or smart phone)

[sms]

On 8/10/2015 9:11 PM, micky wrote:
> In alt.home.repair, on Mon, 10 Aug 2015 08:19:51 -0700 (PDT), trader_4
> <tra...@optonline.net> wrote:
>
>> On Monday, August 10, 2015 at 11:11:45 AM UTC-4, kencarte...@gmail.com wrote:
>>> I am considering buying a NEST thermostat today. I have one of the basic two wire thermostats where I have a white and a red wire. It's the type with the mercury bulb.
>>>
>>> The guy came around from the installers and tried installing a nest three months ago and told me it would not work on a two wire system. I have heard different stories about this. Some say yes it does work, other say it won't work without pulling through a common wire (whatever that is, I am no electrician) My two wires are red and white BUT I also have two other wires that are there, a black and a green one that weren't connected at the thermostat. I am wondering if I could use one of those wires as a common if need be. I would imagine they are for a future install of a heat pump.
>>>
>>> Can anyone advise me on this?.
>>>
>>> Thank you.
>>>
>>
>> Assuming those additional wires run all the way back to the furnace,
>> which is likely, then yes one of them could be used as a common to
>> supply power. If the installer was at all competent, he should have
>> been able to deal with that the first time around.
>>
>>
>> I looked into the Nest a few years ago and from what
>> I saw, there were a huge number of problems, with most of them involving
>> trying to steal power with 2 wire installations. Things like it
>> shorting out, forcing the heat or cooling to full on, regardless of temp.

You need three wires for heat only, common, 24VAC, and RH (request
heat). It's good to have more wires, one for fan-only, and one for RC
(request cool). It would be surprising if the extra two wires you have
don't run back to where the furnace is.

You do not want to install a NEST thermostat in "power stealing" mode
because it can destroy the furnace's controller board.

[micky]

In alt.home.repair, on Mon, 10 Aug 2015 22:23:28 -0600, Tony Hwang

Of course that means terrorist hackers can turn up the heat in your
house. You've been warned.

[Tony Hwang]

High end system has that all taken care off. It won't allow it. It won't
cause freezing or over heating due to AI.

[Mark Lloyd]

On 08/10/2015 11:23 PM, Tony Hwang wrote:

[snip]

> BTW, I have wireless(no wires betweeen thermostat and system) and WiFi
> Honeywell thermostat. I can control it any where in the world using
> internet. using computer or smart phone)

When you do so, are you connecting directly to the thermostat or to a
web server that's controlled by the company? If the latter, then someone
else actually has control over your thermostat in a way that you don't.

It shouldn't be too expensive for a thermostat to contain an embedded
web server, and then YOU connect to IT. I find this very important.

--
Mark Lloyd
http://notstupid.us/

"The basic test of freedom is perhaps less in what we are free to do
than in what we are free not to do." -- Eric Hoffer

[Mark Lloyd]

On 08/10/2015 11:40 PM, micky wrote:

[snip]

> Of course that means terrorist hackers can turn up the heat in your
> house. You've been warned.
>

That's one reason I want a thermostat I control.

BTW, At this moment I happen to be looking at my network router. It's
one computerized thing I can connect to directly to change it's
settings. No company has access.

[Mark Lloyd]

On 08/10/2015 11:33 PM, sms wrote:

[snip]

> You need three wires for heat only, common, 24VAC, and RH (request
> heat). It's good to have more wires, one for fan-only, and one for RC
> (request cool). It would be surprising if the extra two wires you have
> don't run back to where the furnace is.

The new system I got a couple of years ago requires 7 wires, since it
has 2-stage heating and cooling (not heat pump). They actually put in 10
wires (3 available for future use).

[snip]

[Tony Hwang]

Mark Lloyd wrote:
> On 08/10/2015 11:33 PM, sms wrote:
>
> [snip]
>
>> You need three wires for heat only, common, 24VAC, and RH (request
>> heat). It's good to have more wires, one for fan-only, and one for RC
>> (request cool). It would be surprising if the extra two wires you have
>> don't run back to where the furnace is.
>
> The new system I got a couple of years ago requires 7 wires, since it
> has 2-stage heating and cooling (not heat pump). They actually put in 10
> wires (3 available for future use).
>
> [snip]
>

I quit fooling around with wires quite a while ago. Wireless thermostat
is so handy.

[Tony Hwang]

Mark Lloyd wrote:
> On 08/10/2015 11:23 PM, Tony Hwang wrote:
>
> [snip]
>
>> BTW, I have wireless(no wires betweeen thermostat and system) and WiFi
>> Honeywell thermostat. I can control it any where in the world using
>> internet. using computer or smart phone)
>
> When you do so, are you connecting directly to the thermostat or to a
> web server that's controlled by the company? If the latter, then someone
> else actually has control over your thermostat in a way that you don't.
>
> It shouldn't be too expensive for a thermostat to contain an embedded
> web server, and then YOU connect to IT. I find this very important.
>

That is moot point. Still you have to depend on the Internet for remote
access. Nothing in the world is 100%, perfect;y secure. Ever heard of
any system scoring perfect security ratings according to mil-spec.? When
I was retiring best there was B2 rating.
My home network is UTM enterprise class router based, best I could
afford. So far never been compromised by hackers. Any way if there is
unauthorized intrusion, at least I'll know any way as soon as it
happens. BTW, I use wired gateway for outside connection. At least one
less worry not using WiFi method.

[tony944]

"micky" wrote in message news:nklisa5u6k4rllohu...@4ax.com...

In alt.home.repair, on Mon, 10 Aug 2015 08:19:51 -0700 (PDT), trader_4
<tra...@optonline.net> wrote:

>On Monday, August 10, 2015 at 11:11:45 AM UTC-4, kencarte...@gmail.com
>wrote:
>> I am considering buying a NEST thermostat today. I have one of the basic
>> two wire thermostats where I have a white and a red wire. It's the type
>> with the mercury bulb.

Miky: what you have it is just Heat Tst. you need to look for two wire type
Tst.
Two wire can be use also for heat but it require sub control to switch from
heat to cool or wisa wersa
More sophisticated Tst. would not work for you as is, it must have backup
battery.
but yes it can still be hooked up to do the job however person must know
what it is doing.

[micky]

In alt.home.repair, on Tue, 11 Aug 2015 11:02:41 -0600, Tony Hwang

<drag...@shaw.ca> wrote:

>Mark Lloyd wrote:
>> On 08/10/2015 11:23 PM, Tony Hwang wrote:
>>
>> [snip]
>>
>>> BTW, I have wireless(no wires betweeen thermostat and system) and WiFi
>>> Honeywell thermostat. I can control it any where in the world using
>>> internet. using computer or smart phone)
>>
>> When you do so, are you connecting directly to the thermostat or to a
>> web server that's controlled by the company? If the latter, then someone
>> else actually has control over your thermostat in a way that you don't.
>>
>> It shouldn't be too expensive for a thermostat to contain an embedded
>> web server, and then YOU connect to IT. I find this very important.
>>
>That is moot point.

No, it's not.

> Still you have to depend on the Internet for remote
>access. Nothing in the world is 100%, perfect;y secure. Ever heard of
>any system scoring perfect security ratings according to mil-spec.? When

There's perfect, there's almost perfect, and there's far less than
perfect.

[mrbe...@gmail.com]

On Saturday, December 14, 2013 at 7:52:40 AM UTC-8, Ian wrote:
> I am installing a new NEST thermostat, replacing an old two wire mercury bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.
>
> Can anyone tell me which letters on the NEST base (W, Y, O/B, AUX, E, G, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.
>
> Thanks,
>
> Ian

what did you find out? other than this tony dude is a dickhead. why are you such punks?

[mrbe...@gmail.com]

why are you such a dick?

[Oren]

On Fri, 30 Sep 2016 17:24:20 -0700 (PDT), mrbe...@gmail.com wrote:

>why are you such a dick?

Which "dick" do you mean; you must have experience, right?

[mdoy...@gmail.com]

You can not use 2 wire. People are wrong. It wont charge. Will cause issues with your heating. You need a 3 wire. Or you need a crap load of relays. I work in hvac. 90% of my no heat calls with nest is improper wiring. They are garbage. Go with a Honeywell pro 8000

[jason...@gmail.com]

We have a Lennox Elite Gas furnance 2 stage and it is hooked up to an EIM - equipment interface module sending two wires RED and White to the thermostat. If i just run C from panel to the Nest will that power up the nest?

[trader_4]

On Friday, December 23, 2016 at 4:38:29 PM UTC-5, jason...@gmail.com wrote:
> We have a Lennox Elite Gas furnance 2 stage and it is hooked up to an EIM - equipment interface module sending two wires RED and White to the thermostat. If i just run C from panel to the Nest will that power up the nest?
>

Not familiar with the NEst, but for any thermostat that wants power or
where power is an option for the display to light, etc, that is what is
needed, a wire to the common side of the transformer. If you have to
run new wire, I'd upgrade to about an 8 conductor, so you're good for
the future. With an additional wire you could slightly improve the
two stage operation of the furnace. Right now, if there are only two
wires to the thermostat, it's set up as dumb, the system has no way
of knowing if second stage is needed, so it almost certainly is set
up to start on low stage, then if demand for heat isn't met after like
10 mins, then it goes to high stage. With a thermostat that handles
multi-stage, which I think must include Nest, the thermostat makes the
call. If it knows it only needs to go up in temp 1 or two deg, then
it calls for low stage. If it knows it needs to go up 3+ deg, etc,
then it calls for high stage at the start. There is one wire for
stage 1, one for stage 2. Also, typically you have a fan control wire,
so the thermostat can turn on the fan without heating or cooling.
So, to do it right, you'd have:

One wire for heat stage 1
One for heat stage 2
One for fan
One that's connected to one side of transformer
One that's connected to other side (common) of transformer

And if you have AC, then one wire for each stage there.

[destrowa...@gmail.com]

The yellow=Y..
The green=G..
Blue=B

[david....@gmail.com]

I wrote a blog post explaining how to do this. You do not need to pull a common wire in most cases. Try it according to my instructions first, then pull a common wire if you need it, but you really shouldn't since the Nest has a feature called Power Sharing which pulses closing of the circuit to draw current when it needs to charge itself.

Post with instructions: https://dhariri.com/posts/58977ea0d1befa66e7b8e119

[gafu...@gmail.com]

Today I install nest thermostat. I took out the old one.i saw only two wires. White and yellow..so I put those white in W1 and yellow one at Y..am I doing correct..advise me plz

[gafu...@gmail.com]

Y

[gafu...@gmail.com]

Same thing happen to me

[Mr Fuxitup]

On 10/04/2017 12:31 AM, gafu...@gmail.com wrote:
> Today I install nest thermostat. I took out the old one.i saw only two wires. White and yellow..so I put those white in W1 and yellow one at Y..am I doing correct..advise me plz

If this is a 24 volt heat only system, I'm going to *guess* you should use the Rh and W terminals.

Were the terminals labeled on your old thermostat?


If you have a millivolt furnace system, the nest probably wont work with it.

[trader_4]

Good grief. RTFM. The install instructions will certainly clearly
explain how to hook it up to a two wire system. IDK how it works now,
but years ago there were big problems with using it with two wires.

[Tekkie®]

trader_4 posted for all of us...

+1

--
Tekkie

[moderator]

gafuster appears to be a driveby shooter.  He prolly won't be back. We'll just close the ticket.

-mode...@alt.home.repair

[Scott]

On Saturday, December 14, 2013 at 7:52:40 AM UTC-8, Ian wrote:
> I am installing a new NEST thermostat, replacing an old two wire mercury bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.
>
> Can anyone tell me which letters on the NEST base (W, Y, O/B, AUX, E, G, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.
>
> Thanks,
>
> Ian

I just replaced the same kind of old thermostat with Nest. The Nest info was no help for this. I made it work by finding the two wires where they connected to the furnace. At that connection there are letters corresponding to the connections on Nest. In my case it was R and W. My old wires were the same color so I could not easily distinguish which was which at the thermostat end so I ran two new wires (red and white 18ga. solid) by taping them to the old wire and pulling it through to the furnace. I attached the R wire to the Rh and the W wire to the W1 connections on Nest. R to Rh, W to W1. It works just fine. I'm baffled at all the comments on this thread insisting it could never work.

[trader_4]

When you have just a two wire thermostat, which wire is which doesn't matter,
it's AC. You'd think Nest would have told you that to avoid all the angst.
I hope they work better now, back in the early days there were big, big,
problems, especially when using them with just two wires, where they try
to power themselves.

[Tekkie®]

trader_4 posted for all of us...


>

They were acquired by Honeywell.

--
Tekkie

[openso...@gmail.com]

On Saturday, December 14, 2013 at 10:52:40 AM UTC-5, Ian wrote:
> I am installing a new NEST thermostat, replacing an old two wire mercury bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.
>
> Can anyone tell me which letters on the NEST base (W, Y, O/B, AUX, E, G, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.
>
> Thanks,
>
> Ian

i can tell you. one of the wires will go to w1 , the 2nd wire will be your common C