Heat Pump Emergency Heat - The Basics

HVAC Q&A: What is My Heat Pump’s Emergency Heating Setting?

Posted on: March 18, 2015 | by: HVAC.com September 4, 2019

In today’s HVAC Q&A, we are going to address Emergency Heat. If you’ve owned a heat pump for a long time, you might already know how this feature works. But if you’re a new heat pump owner like Jessica in Chicago, you probably have some questions. Jessica writes:


“Dear HVAC.com experts,


I recently had a heat pump installed in my home and noticed an emergency heat switch on the thermostat. What is it? How does it work? When should I use it?



Before we talk about what the Emergency Heat (also know as “auxiliary heat” or “aux” heat on some thermostats) setting on your heat pump thermostat is, let’s take a moment to explain exactly what a heat pump does.


Heat pumps heat and cool your home by moving or “pumping” heat out of the house in the summer and into the house in the winter. When temperatures fall, it’s harder to extract heat from the outside air, so heat pumps require a secondary heating source, which is usually located in the indoor unit. During the colder months, your heat pump (first stage heat) automatically taps into the Emergency Heat source (second stage heat) in order to heat your home.


Now that you know a little bit more about heat pumps, let’s talk about Emergency Heat.




What Is Emergency Heat?


When your system runs solely on its second stage heat source, it’s using Emergency Heat. Emergency heat is the second stage of heat that your thermostat taps into when it is too cold for your heat pump to extract heat from the outside.


Since this second stage heat source is designed to be just that, secondary, running your heat pump on emergency heat increases your HVAC system’s energy usage and results in escalating energy bills.


How Does Emergency Heat Work?


In most cases, a heat pump’s second stage heat source is electric, but it can also be gas or oil. Think of an electric second stage heat source like a strip of heated coils in a toaster within your air handler. If your second stage heat source is oil or gas, it’s probably hooked into your furnace.


When you set your thermostat to Emergency Heat, your system bypasses the heat pump and directly accesses either the electric heat strip or gas/oil furnace heat. For electric systems, this basically turns your air handler into an electric furnace, which can be costly.


When Should I Turn On Emergency Heat?


Many people assume that Emergency Heat is designed to be turned on by the homeowner during especially cold weather, but that’s not quite right. It’s designed to only  be switched on by the homeowner in emergency situations, when something happens to the first stage heat source — your heat pump.


For example, if the limb of a tree is weighed down by snow and falls on your outdoor unit, damaging it, it’s time to switch on your Emergency Heat and call an HVAC professional. If your heat pump is malfunctioning and shorts out or freezes over, flip the switch and call for an HVAC maintenance appointment.



For all-electric systems, your Emergency Heat system should keep you warm until your heat pump can be fixed. For gas or oil furnace second stage systems, you should be fine for longer periods of time.


Use It Right & Save Yourself Money


Now that you know what Emergency Heat is for, make sure you’re using it right. Don’t use your Emergency Heat setting unless your heat pump is damaged. Save yourself money by keeping your thermostat setting on “Heat” during the winter, and if you need to switch to emergency heat, call an HVAC professional as soon as possible to get your heat pump back in shape.


Have you been using your Emergency Heat setting improperly? Have you ever had to use it in an emergency?


Learn more about heat pumps and other types of heating systems today. Check out our complete guide to heating here.



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