Emergency heat vs. auxiliary heat: Why you need to know the difference!

When outside temperatures drop below 40 degrees, your heat pump runs on one of two settings: emergency heat or auxiliary heat.

What’s the main difference between the two?

  • Auxiliary heat is when a secondary heat source turns on automatically
  • Emergency heat is when you turn on a secondary heat source manually

We’ll explain why in more detail later on. First, let’s start with how auxiliary heat works and how it’s activated.

How auxiliary heat warms your home in cold temperatures

Heat pumps transfer outdoor heat to the inside of your home (like a giant heat sponge).

However, when temperatures drop below 40°, a heat pump relies a backup heat source to warm up your home.

This setting is called the auxiliary heat mode, and it’s automatically enabled after you raise the room temperature by 2° or more in heat mode.

Your auxiliary or backup heat is either supplied by an electric heating coil (the most common) or a gas furnace (also called a hybrid heat system). These supplement the heat supplied by your heat pump to keep your room at the desired temperature.

Auxiliary heat mode is normal and OK. But if you switch to the manual setting “emergency heat,” you’ll actually waste energy and money.

Let’s look at why

Why the the emergency heat setting wastes money

Emergency heat (EM HEAT) mode on thermostat. Image source: www.energyvanguard.com

Emergency heat manually locks down your heat pump and switches 100% of your heating to the secondary (backup) heating source.

So when it’s cold outside, you should just turn on emergency heat, right?


Because emergency heat forces your secondary heating source to pick up all the slack, it means you’re heating your home on a low-efficiency heat source.

How inefficient are we talking? Well, electric resistance coil heaters are 3 times less efficient than a heat pump. If you’re running on emergency heat mode for long periods of time, you’ll see a much higher energy bill.

Even if you have a hybrid system (though it’s much better than electric coil heaters), you’re still not going to be as energy efficient as you would if your heat pump was helping warm your home.

In aux mode, heat pumps continue to extract heat, even from cold outside air, so there’s no reason to have your secondary heat source do 100% of the work.

Only use emergency heat if your heat pump is broken

The only time you should use emergency heat is when there’s an emergency (hence the name!).

If your heat pump isn’t working properly, due to factors like a broken compressor or damage from a storm, it’s OK to switch your thermostat to emergency heat mode.

And if that’s the case, you should contact us so we can send a professional heating expert to fix your heat pump right away.

Have more heat pump or thermostat questions?

We’d love to answer them. Contact Santa Fe Air with all of your questions. Or, if you’re in a hurry, call (913) 856-5801, and we’ll send someone to your home ASAP.

We’ve been making Kansas City families comfortable since 1987.