# Leave "E" wire disconnected from thermostat?



## Done That (Apr 28, 2011)

Well it sounds like you have a package heat pump, based on the presence of the "O" terminal for the reversing valve. The "E" terminal is there as you say to turn on emergency heat, which in your case is probably electric strip.

You should be able to manually switch your thermostat to emergency heat....for example if the compressor was not running so you could still get heat.

You would lose this capability without having your new stat have an E terminal. Yes, you could simply not connect the E and protect it, or also disconnect it at the outdoor unit.

I must be missing something because you should be replacing with a heat pump thermostat that should also have an E terminal??

Looking again at your picture the plastic tab at the bottom when moved to "SUPL HT" should energize that E terminal.


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## Evan1127 (Feb 28, 2012)

Great, thank you for your help.


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## beenthere (Oct 11, 2008)

Post brand and model number of your new thermostat.


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## Evan1127 (Feb 28, 2012)

It's the new Nest learning thermostat. http://www.nest.com/

I am friendly with someone on the development team, which is why I am considering switching out my thermostat (besides it looking like a quality product). So I either get it and forfeit my emergency heat option (which I don't think I'd mind) or just stick with the one I have now.


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## beenthere (Oct 11, 2008)

It my become an antique soon. Your friend will know why I said that.


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## Evan1127 (Feb 28, 2012)

How do you mean?


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## thermostat (Feb 18, 2012)

This chart shows what systems the Nest thermostat is compatible with. The chart was created by trying all of the different combinations on the Nest compatibility tool Your system should be compatible with the nest thermostat. Do you know where the E and the W2 wires from your thermostat are landed at in the air handing unit?


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## beenthere (Oct 11, 2008)

Talk to your friend in R&D.


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## Evan1127 (Feb 28, 2012)

No, I don't know where the E and W2 wires are landed.

I used the compatibility tool, and it says I'm compatible when I leave the E unchecked, but then says I am incompatible once I check the E.


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## hvactech126 (Nov 11, 2010)

Besides your friend, why would you want that thermostat? There are much better thermostats that can do what the NEST can and much more. They also do what the nest cant do which is operate your system properly by providing you the option of emergency heat.

I think Beenthere may know about a new version coming out? (just guessing as he has me intrigued now)


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## beenthere (Oct 11, 2008)

Nope. They're being sued for patent/technology infringements. I believe 7 infringements.


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## Evan1127 (Feb 28, 2012)

I've read about the patent infringements. One of them is something like "displaying grammatically complete sentences while programming a thermostat". I'm not even sure how you can get a patent on that. In any case, the patent suit doesn't sway me in one way or another.

hvactech126, can you point me in the direction of a similar thermostat? I suppose I wouldn't be closed to the idea of another model, but I have personally not found one that can do what Nest can.


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## hvactech126 (Nov 11, 2010)

what feature of the nest do you want most? internet capability? sleek design? If you are looking for a thermostat that can program itself, then that is probably not going to happen. Programming a thermostat is not hard to do. You do it once and then it is done.


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## Evan1127 (Feb 28, 2012)

So then there aren't thermostats that "can do what the Nest can do and much more". You just don't think it's worth buying the Nest.

I appreciate the help with my original question about the "E" wire, but I didn't ask to be talked out of my purchase because of the personal feelings of those responding. I shared the model I am looking at assuming that it was relevant to my question.


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## hvactech126 (Nov 11, 2010)

Simply put... no, the nest is not the proper thermostat for your application. Most professional thermostats now have some sort of recovery feature that "learns" how your home heats and brings the temp up to the set temp at the programmed time. Nests claim to fame is that you don't have to program it for the time changes, but actually you are programming it and it takes a week or so to "learn" what times and temps that you make changes at the thermostat so you are programming it. There are other thermostats that do much more then the nest and allow you to control compressor and aux heat lockout temps. This is a better feature in that you can see more energy savings by controlling these options. Many thermostats now have access through internet protocol. 

Again. The nest is not the correct thermostat for your application.


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## beenthere (Oct 11, 2008)

The brand and model number is important.

That thermostat is not an appropriate one for a heat pump with electric aux heat.

When you ask a question to over 100,000 people, your not gonna get just a narrow answer.


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## JRaper (Jul 30, 2017)

I know this is years and years later but I figured I would make a comment anyway. The heat pump uses W2 and/or E to turn on Aux Heat. In fact the W2 and E are connected to the same terminal in the air handler (sometimes you will even see these 2 with a jumper between them on the thermostat). You can safely leave E disconnected and not lose any function of your heat pump/emergency heating. The nest is 100% compatible with that system. The O/B wire is the reversing valve that controls if your heat pump is on for cooling or Heating. The Y wire turns the compressor on for both AC/Heat. R/RC/RH is power (mostly you will find just RH or RH/RC connected together. You would only need a separate wire for RC and RH if you have a dual transformer system which is uncommon. C Wire is optional but does provide power to your thermostat so you don't have to use batteries, it is only required on some thermostats like the NEST that has no batteries of its on or if you are using a Z-Wave thermostat and want to use it as a repeater. G is your Fan. 

I'm sure its too late to help with the original post but maybe someone will benefit from this answer.:vs_bulb:


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## supers05 (May 23, 2015)

*Re: Leave &quot;E&quot; wire disconnected from thermostat?*



JRaper said:


> I know this is years and years later but I figured I would make a comment anyway. ....


Dead post walking..... 

PS. It was mentioned that it was a 2 stage unit. Without the model number, or at least knowing how the thermostat wiring is connected at the unit, E may be required to engage backup heat. (with w1 and w2 on the 2 stages.) 

The nest is only compatible if it's a single stage with backup, AND you're using the common if it has a control board for the thermostat wiring. 

Cheers!


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## GGCG (Feb 14, 2021)

JRaper said:


> I know this is years and years later but I figured I would make a comment anyway. The heat pump uses W2 and/or E to turn on Aux Heat. In fact the W2 and E are connected to the same terminal in the air handler (sometimes you will even see these 2 with a jumper between them on the thermostat). You can safely leave E disconnected and not lose any function of your heat pump/emergency heating. The nest is 100% compatible with that system. The O/B wire is the reversing valve that controls if your heat pump is on for cooling or Heating. The Y wire turns the compressor on for both AC/Heat. R/RC/RH is power (mostly you will find just RH or RH/RC connected together. You would only need a separate wire for RC and RH if you have a dual transformer system which is uncommon. C Wire is optional but does provide power to your thermostat so you don't have to use batteries, it is only required on some thermostats like the NEST that has no batteries of its on or if you are using a Z-Wave thermostat and want to use it as a repeater. G is your Fan.
> 
> I'm sure its too late to help with the original post but maybe someone will benefit from this answer.:vs_bulb:


Just wanted you to know that your comment was very helpful. I’ve been looking for days and you were the only one that answered my guestion, Thanks!


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