The Best Guide On Knowing What Is Aux Heat

You probably have your experiences with your appliance malfunctioning or flashing lights you don’t have idea what it means. Your response to this thing could determine how well do you know about your appliances.

If your initial reaction is not doing anything to it, accidents might happen. Or if you do something about it but your action is wrong, then it could lead to destructions and accidents. You have to know what the light in your appliance means.



Does it mean a bad thing or does it mean a good thing? Reading product description is not enough, further reading information about it will help you know what to do with it. Every little thing about your appliance in your home is very important because all of it has functions.

These functions should be mind because it might not function one day and you can’t call a technical maintenance to help you.


Have you ever wondered what an aux heat in your thermostat is? If you see the Aux heat light, do you know what to do? In this article, you would be informed of what an auxiliary heat is and its importance.

Many of us don’t know what it highly means so it’s essential to be informed so that the next times we encounter an Aux Heat light, we would know its function and not just disregard it.

What is Aux Heat?

First, it should be noted that your thermostat has heat sources, the main source and auxiliary source. For example you have this appliance and its main heat source is an off-peak electric and its auxiliary source is a gas-fired furnace. Now, we would be focusing on the auxiliary heat source.

Auxiliary means the "secondary" source of heat. The balance point of an air source heat pump is usually about 35 degrees. When this heat pump could no longer produce heat, the thermostat turns on the electric heat strips to provide needed heat. The thermostat then turns on the AUX Heat light. So again, auxiliary heat is the second source of heat.


When your Aux Heat is on, it means that you are using an auxiliary source of heat that is more powerful yet more expensive. The usage of aux heat can cost twice as your main source. Normally, the auxiliary heat source turns on if the main heat source is not functioning.

This is a more detailed explanation of that: every few hours the heat pump needs to defrost the outside unit and reverse itself. While it’s in the process of defrosting, the auxiliary heat turns on to provide the heat you need. If the aux heat source doesn’t turn on, no warm air would be produced and it will make the room temperature drop.

Technically, the defrost mode is when the heat pump reverses to air conditioning mode so that the outside coil will be warmed up. So, to avoid icy air going through the vents, the heat strips energizes and the auxiliary heat turns on.


So basically, the job of auxiliary heat is to assist the heat pump maintain its set temperature.

We already talked about auxiliary heat being twice as expensive as main heat source, but there are thermostats that can control aux heat; it is called the auxiliary lock out temperature.

If you set your lockout temperature to 40F/4.4C then the auxiliary heal turns on when outdoor temperature drops below your lockout temperature.

How does Aux Heat Differs from Emergency Heat?

Confusion between these terms is inevitable. We tend to interchange the terms and sometimes confuse one term from the other. If you think the two doesn’t have a difference, then you are mistaken because they do have distinct characteristics.

The AUX in your thermostat is the indicator that you are running the heat strips set to heat. Emergency heat on the other hand is the switch that turns off the heat pump and runs the auxiliary heat source.


Turning on electric heat strips manually is another one signaled by Emergency Heat (EM in your thermostat).

So again, AUX heat is the indicator and EM is the switch setting.

What to do When Aux Heat is on?

Do not worry too much, do not freak out. Your thermostat is not damaged or. Again, it used a back-up heat source to keep you warm from cold temperature. It may cost twice as the main heat source, but it’s actually not going to damage your thermostat.

In conclusion, AUX heat differs a lot from Emergency Heat. I hope this article is informative enough. In addition, if you are too conscious of how much your electric bill is going to cost, you can try an alternative.


Use a Heat Pump Balance. It is a feature for home which has a heat pump with aux hat. HPB monitors how your pump is doing. It helps to minimize how often you use your auxiliary heat and make predictions as when to use it in the near future.

Heat Pump Balance provides you four choices to choose from:

  • Maximum Savings – When you are saving energy, this is the best setting. In this mode, the thermostat gives the heat pump longer time to achieve the target temperature.
  • Balanced – Although the heat pump is given enough time to work too, this setting will still turn on the aux heat quickly.
  • Maximum Comfort – This is the default setting which gives you higher aux lockout. This setting also allows your thermostat to achieve the temperature you set.

To close this article, keep in mind that the work of auxiliary heat highly depends on the efficiency of your system. I hope that you learned a lot. If you have comments just feel free to write it down in the comments section.

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