W1, W2, & E

I got this question via email (edited slightly for length):

Some things I've done because I've been taught to do them yet I don't know why I do them. One of those things is putting a jumper between w1/e and w2. Sometimes, in the case of a Goodman for example, I've been taught to combine the brown wire along all the whites at the air handler. Do you mind just clarifying the whole situation with w1/e jumped to w2? And also maybe x2 on some stats? Thanks for your help.
— J

Back in the early 2000s, when I was the lead trainer for another company, some of the most common miswiring issues had to do with electric heat. So much so that I created a bunch of different wiring diagrams with a fancy program called “Microsoft Paint” to illustrate how to wire different combinations of equipment. Here is one of them:

In older thermostats (older than the diagram shown here), there were no installer setup programs where you could designate the type of system the thermostat was connected to. Each terminal performed a particular universal function, and you would configure the operation based on how you wired it up. Which terminals you connected and where, which ones you left open, and sometimes, which ones you jumpered out.

So, first, let's give a quick look at the meaning of each terminal:

W – When you see a W terminal, it just means heat. Usually, you will only see W when the control only has one stage of heat.

W1 – Means first-stage heat. In a heat pump, first-stage heat is the same as the first-stage cool. It just means the contactor/compressor is turning on. Whether that is heat or cool is actually dictated by whether or not the O/B terminal is energized. That is why, on many old thermostats, you would jumper Y1 and W1 in a heat pump application.

W2 – Means second-stage heat. It could be the first stage of heat strips in a common southern heat pump, the gas furnace backing up the heat pump in a modern “hybrid heat” application, or just a second heat strip bank in the case of a straight electric system. W2 is generally called on based on a temperature differential between setpoint and space, outdoor temperature, or run time.

W3 – This is just the next stage of heat after W2.

E – Is emergency heat, usually just a way to manually drive on what would normally be the secondary form of heat without stage 1 heating.

Emergency heat only makes sense when there is some sort of secondary heat source. Even then, it only helps if the secondary heat source is sufficient to heat the space, as in the case when the secondary is a furnace, Hydronics, or a large heat kit. In Florida, most of our units have 5KW auxiliary heat, which will never be sufficient to heat a home in an “emergency.”

Many of these other terminal designations are a holdover from a time when all the controls in the thermostat and defrost board were electromechanical. Much of it was for indication/trouble lights, and some of it was for the thermostat to perform staging based on outdoor temperature because run-time logic was not available. So, for your X2 question, have a look at the thermostat and diagram below.

In the modern thermostat, they have usually relegated these staging configurations and terminal designations into the installer setup, and every thermostat is a little different. In general, in the south, we jumper W2 to E because they truly are the same. In some cases, this does nothing; in others, it just ensures that the aux heat comes on quicker if the user chooses emergency heat.

Are there some cases where emergency heat could be totally different than aux heat? I'm sure; I have just never seen one personally. Like usually, it all comes down to knowing your particular piece of equipment and your controls; reading the installation instruction is a good first step.

—Bryan

 

 

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4 responses to “W1, W2, & E”

  1. A good answer for a good question , as a installer myself I like to know exactly what function of each part I install to know exactly how it operates.

    • If I have an older system that includes W1 W2 and a Y1 how can I install these on my new thermostat. There are places for all of my labled wires but I always encounter the note “if you have w1, w2, and y1 cables, you need to consult a technician… I have model number available if this helps. Thank you.

  2. Wow, I have the issues gentleman. my old thermostat has have w1, w2, and y1 cables,
    how can I install these on my new thermostat? my guess jumping it out.

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