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Which Thermostat Wire Is Responsible For Emergency Heat?- What You Need To Know

Which Thermostat Wire Is Responsible For Emergency Heat?- What You Need To Know

Thermostats typically have multiple wires that are not always easy to distinguish. During the cold winter months, you may want to turn on your emergency heat. Understanding how it works entails understanding which wire controls it behind the scenes. This is why we posed this question to experts, and here is their response.

The color of the emergency heat wire varies from manufacturer to manufacturer, making it difficult to distinguish. Noting which wire is inserted into the terminal marked “E” is the best way to spot the emergency heat wire.

There is more to know about your thermostat’s emergency heat setting and how to maximize the heat functionality of your thermostat. Continue reading to learn about our well-researched findings.

What Exactly Is Emergency Heat?

Which Thermostat Wire Is Responsible For Emergency Heat?- What You Need To Know

Thermostats are typically equipped with two heat sources: primary and secondary. The heat pump installed outside generates primary heat, which is the thermostat’s first port of call for heating your home.

In reality, the heat pump does not generate heat; rather, it extracts heat from the outside air and directs it indoors. When the outside temperature drops below 35 degrees Fahrenheit, the secondary heat source, usually a gas furnace or an electric heat strip, automatically kicks in to assist.

Some thermostats label this as aux or auxiliary heat, indicating that heat is drawn from both primary and secondary sources. As the name implies, emergency heat is only used in emergency situations.

Just as you wouldn’t use an emergency exit as a regular passageway, emergency heat should only be used in situations where the heat pump is damaged or the compressor is broken.

Heat pump failure is more common than you might think. Because the heat pump is outside, it is vulnerable to freezing in extremely cold temperatures, which could result in damage.

When set to emergency heat, the thermostat only uses the secondary source because the heat pump is turned off. It’s worth noting that your thermostat uses a lot more energy in this mode than it does in the aux mode.

Which Thermostat Wire Is Responsible For Emergency Heat?

Your thermostat’s heat pump is equipped with a number of wires that must all be connected to the thermostat for it to function properly. It would be extremely useful to be able to distinguish the emergency heat wire from the others.

The “E” wire represents the emergency wire. Make a mental note of the wire inserted into the “E” terminal on the thermostat’s wall plate. You could take a picture before attempting to remove any wires.

What Color Is The Emergency Heat Wire On A Thermostat?

Which Thermostat Wire Is Responsible For Emergency Heat?- What You Need To Know

In most thermostat systems, a color code is considered standard. This is critical for making installations and repairs easier, especially since thermostat manufacturers are not typically involved in installation.

Surprisingly, there is no universally accepted color for emergency heat. It would all depend on the manufacturer of your thermostat’s heating pump, as well as your installer if they did their own rewiring.

Is The RC Wire The Same As The C Wire?

The “RC” wire powers your thermostat’s cooling function, and the “R,” “RH,” and “RC” wires power your thermostat’s heating and cooling systems in general.

The “C” wire has no connection to any of the “R” wires, including the “RC” wire. The “C” stands for common wire, which serves a completely different purpose than the “R” wires.

Previously, thermostats were on/off devices that did not always stay on. Thus, the batteries were sufficient to power them, and the “R” wires provided power from the batteries to the thermostat.

The need for a continuous power supply to the thermostat became necessary with the introduction of smart thermostats that are intended to be continuously on due to their increased functionalities. In comes the “C” wire.

While the “R” wires supply power, the thermostat’s other wires must be able to connect back to the control board to complete a circuit. These wires use the “C” wire as a return path. This circuit ensures that the thermostat receives power at all times.

It should be noted that not all smart thermostats require a “C” wire. Models lacking the “C” wire can run on batteries. Please consult the owner’s manual for your thermostat to determine whether it can operate continuously without a “C” wire.

So, while the “R” wires power the thermostat’s heating and cooling functions, the “C” wire, if your thermostat has one, is the reason your thermostat stays on all the time.

What Do W1 And W2 On A Thermostat Mean?

Your thermostat’s heating function is controlled by the “W” wires. While the “RH” wire provides the necessary power for heating, the “W” wire regulates the temperature. When your thermostat detects a need for additional heat, the “W” wire sends the signal to your HVAC system.

Your thermostat may have a single “W” wire or two: the “W1” and “W2” wires. Your thermostat has a two-stage system if it has both. “W2” is the second stage, and it warms up the house faster on extremely cold days.

Is The White Wire Connected To W1 Or W2?

The “W” wire is the white wire. This is simple if your thermostat has only a single “W” terminal. It’s understandable to be perplexed when you have both “W1” and “W2” terminals and a single white wire. Simply insert the white wire into the “W1” terminal if this is the case. A brown wire is also likely to be present. This is routed to the “W2” terminal.

What Do R And RC Mean On A Thermostat?

Depending on the thermostat manufacturer’s preference, your thermostat may have a “R” wire or both “RC” and “RH” wires. The “R” wires are for powering your thermostat. If you only have a “R” wire, a single transformer powers both the heat and cooling functions of your thermostat.

Where there are both “RH” and “RC” wires, the “RH” wire powers the heating system while the “RC” wire powers the cooling system, with both wires using different transformeds. It’s helpful to remember that “RH” stands for “red heating” and “RC” stands for “red cooling.”

How Do You Make A Thermostat Jump For Heat?

Knowing how to deal with such days will come in handy if your thermostat fails. Jumping/bypassing your thermostat is a surefire way to get the heat back on.

The outer body in front and the wall plate comprise the majority of thermostats. You must remove the front to gain access to the wires. If your thermostat is screwed to the wall, you may need to unscrew it.

While your thermostat is powered by a 24-volt system that is unlikely to cause serious electric shock, it is best to turn off the power before handling the thermostat wires.

By connecting the “R” and “W” wires on your thermostat, you can turn on the heat. Keep in mind that “R” controls the heating and cooling functions, whereas “W” controls the heat. To jump the heat, connect the ends of these two wires. You can accomplish this with a variety of tools.

Jumpers With Magnets
Magnetic (or “mag”) jumpers are made up of two points that are connected by a single wire. Just connect one end to the “R” terminal and the other to the “W” terminal.

Thermostat Cable
A thermostat wire with each end exposed will come in handy here. Insert each exposed end of the wire into the “R” and “W” terminals while holding the insulated part of the wire.

Alligator Jumpers
These can be used in the same way as mag jumpers, but with larger terminal screws.

You can also remove the “R” and “W” wires and twist them together to form a wire nut. The main thing is to connect the ends of the “R” and “W” wires. If you try any of these and still don’t feel any heat, the problem could be with the control board rather than the thermostat.

What Happens If You Wire A Thermostat Inadequately?

Which Thermostat Wire Is Responsible For Emergency Heat?- What You Need To Know

If you set up your thermostat incorrectly and connect the wires to the incorrect terminals, your thermostat system will not function properly. A single wire-terminal mismatch is enough to cause problems.

Incorrect wiring can cause an increase in energy consumption, an uncomfortable and/or oscillating temperature in the home, or a completely non-functional thermostat system.


If your thermostat is not warming up the house despite being turned on, you should consider jumping it for heat. When working with your thermostat, keep in mind that the wires must be properly matched to the corresponding terminals. Before making any changes, it’s a good idea to take a picture of the wiring.

Which Thermostat Wire Is Responsible For Emergency Heat?- What You Need To Know

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Written by HVAC Contributor

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