Installing NEST Thermostat - two wires

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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The yellow=Y.. The green=G.. Blue=B
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.