Installing NEST Thermostat - two wires

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

No, it's not.

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

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On 8/10/2015 9:11 PM, micky wrote:

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.
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On 08/10/2015 11:33 PM, sms wrote:
[snip]

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

I quit fooling around with wires quite a while ago. Wireless thermostat is so handy.
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"micky" wrote in message

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.

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.

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

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.

I'm sure you're right.
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On Saturday, December 14, 2013 at 7:52:40 AM UTC-8, Ian wrote:

what did you find out? other than this tony dude is a dickhead. why are you such punks?
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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?
On Saturday, December 14, 2013 at 7:52:40 AM UTC-8, Ian wrote:

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On Friday, December 23, 2016 at 4:38:29 PM UTC-5, snipped-for-privacy@gmail.com wrote:

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.

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The yellow=Y.. The green=G.. Blue=B
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I wrote a blog post explaining how to do this. You do not need to pull a co mmon wire in most cases. Try it according to my instructions first, then pu ll a common wire if you need it, but you really shouldn't since the Nest ha s a feature called Power Sharing which pulses closing of the circuit to dr aw current when it needs to charge itself.
Post with instructions: https://dhariri.com/posts/58977ea0d1befa66e7b8e119
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Same thing happen to me
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On Saturday, December 14, 2013 at 7:52:40 AM UTC-8, Ian wrote:

bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.

C, etc) they will map to? It has to be the most basic of installations; op en or close the circuit.

I just replaced the same kind of old thermostat with Nest. The Nest info wa s no help for this. I made it work by finding the two wires where they conn ected 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 thermos tat end so I ran two new wires (red and white 18ga. solid) by taping them t o 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 insistin g it could never work.
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On Monday, October 30, 2017 at 11:04:54 AM UTC-4, Scott wrote:

y bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.

, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.

was no help for this. I made it work by finding the two wires where they co nnected 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 th e same color so I could not easily distinguish which was which at the therm ostat 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 wi re 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 insist ing it could never work.
When you have just a two wire thermostat, which wire is which doesn't matte r, 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.
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trader_4 posted for all of us...

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.

They were acquired by Honeywell.
--
Tekkie

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