Will my heat pump automatically switch to emergency heat?

Author: Paige Trantow PhD  |  Last update: Friday, June 5, 2026

It also serves as a secondary heating system that can switch on if your heat pump isn't able to maintain your desired indoor temperature. Most heat pumps will turn on emergency heating mode automatically when conditions require it.

At what temperature does a heat pump switch to emergency heat?

This heating method works incredibly efficiently until the outdoor temperature reaches about 35 degrees. At this point, the heat pump has difficulty extracting enough heat from outside to keep up with the thermostat setting. This is when many people assume it's time for switching their heat pump to emergency heat.

Does a heat pump automatically switch to auxiliary heat?

If the temperature outside is below freezing, your heat pump's auxiliary heat system will come on automatically - whether that's a gas furnace or electric heat strips. But there are some things you can do to minimize the need for aux heat. Make sure your heat pump is correctly sized for your home.

Does emergency heat come on automatically?

Your thermostat automatically switches on the aux heat. You have to turn on the emergency heat manually. It usually turns on when the outside temperature drops and the heat pump alone is insufficient. It is mostly used when your primary heat system or first-stage heating has stopped working.

What happens when a heat pump thermostat is switched to emergency heat mode?

When you manually set the emergency heat on your thermostat, your system bypasses the heat pump and directly accesses either the electric heat strip or the gas or oil furnace. With electric systems, your air handler turns into an electric furnace.

What is Emergency Heat Mode And When To Use It On A Heat Pump

How long can you run emergency heat in your house?

There's no specific timeframe for using the emergency heat setting. If you need it for a few hours, the system should be fine. Or, keep it on until the unit thaws out or is fixed.

Does Honeywell thermostat automatically turn on emergency heat?

It has a second temperature sensor. If the temperature in the house drops two degrees the emergency heat comes on. Most thermostats have a small light that comes on when it goes to emergency heat mode.

What temperature is too cold for heat pumps?

Most standard heat pumps will function at 100% efficiency until the outside temperature reaches about 40° F. However, when the temperature dips below this, most heat pumps are not able to maintain efficiency. They become much less effective at temperatures between 20° F to 30° F.

What triggers emergency heat?

However, most modern thermostats are designed to automatically activate auxiliary heat when needed, typically in three scenarios: When the heat pump can't recover heat quickly enough due to extreme cold. When the thermostat set point is manually adjusted significantly higher.

Why does my heat keep switching to auxiliary heat?

The auxiliary heat setting on an HVAC unit usually turns on when you need heat fast. If this secondary heating system is constantly running, it may mean that the weather outside is very cold or that the thermostat is set higher than normal. It's also possible that a part of the heat pump is malfunctioning.

Why is my heat pump not switching to auxiliary heat?

Aux Heat Will Not Turn On

One of the most common causes of a heat pump system or auxiliary heat not turning on is a blown fuse or tripped circuit breaker. Start by checking your fuse box or circuit breakers.

Can a heat pump switch from heating to cooling automatically?

The Auto mode on heat pumps allows the heat pump to decide whether to heat or cool the space, but it doesn't always know best. “Auto” mode could cause your heat pump to heat on a cool summer night or cool on a sunny fall or winter afternoon. To avoid accidentally cooling during the fall and winter, use “Heat” mode.

What is the drawback of emergency heat?

High energy bills

The cost of running your home on Emergency Heat would be astronomical. Turning to this setting switches the source of your heat from the heat pump to the electric heat strip, which is significantly less efficient and more costly.

What is the difference between auxiliary heat and emergency heat?

Auxiliary Heat – This is the secondary heat source that turns on automatically. Emergency Heat – This is when you turn on the secondary heat source.

Should I switch my heat pump to emergency heat during ice storm?

Frost and ice shreds may also collect around the heat pump. However, if extreme amounts of ice and snow buildup over the unit, it's strongly recommended to switch it off or to 'emergency heat' to remove the snow. The easiest way to get the snow off the heat pump is by pouring warm water over time.

Why is my emergency heat blowing cold air?

There are a few possible reasons your heat pump might be blowing cold air: Your heat pump is in defrost mode. There's an issue with your heat pump. It's below freezing, and you need a backup heat source.

Does emergency heat kick on automatically?

The difference between emergency heat and auxiliary heat is that emergency heat has to be switched on manually and should only be used in temperatures of 30 degrees or below. However, auxiliary heat will kick on automatically to help heat your home more quickly if there is a sudden drop in temperature.

What are 3 signs of a heat related emergency?

The warning signs of the most serious stage of a heat-related illness (often called heat stroke or sun stroke) vary but may include: * Vomiting. * Confusion. * Throbbing headache.

Should I put a heat pump on emergency heat below 40 degrees?

Short answer: No. Switching your thermostat to emergency heat or “em heat” just because it's cold outside will just raise your energy bills like crazy. Don't use emergency heat mode unless your heat pump stops heating your home altogether. If that happens, contact a professional heat pump repairman for help.

At what temperature does a heat pump switch to auxiliary heat?

Auixiliary Heat will turn on automatically when heat can no longer efficiently transfer heat from the outside air to heat pump. This is when the outside is around 35-40 degrees and the indoor temperature is around three degrees cooler than the thermostat setting.

Should I turn off my heat pump in extreme cold?

People do not need to turn their heat pumps off. Residents should make sure their supplemental home heating systems are on and operating. Set the thermostats to a degree or two lower than heat pumps.

What is the 20 degree rule for heat pumps?

Simply put, it means you should never set your thermostat for a temperature more than 20 degrees cooler than the outside air. Why not? Most air conditioning systems can only handle a 20-degree difference between the outside and inside air temperatures.

How does a heat pump know when to switch to emergency heat?

Emergency heat is the secondary heating system that your heat pump switches to when it can no longer efficiently extract heat from the outside air due to extremely cold weather. This mode is activated when the heat pump malfunctions or when the heat pump stops working.

What happens if auxiliary heat runs too long?

This can cause concern, as auxiliary heat typically is not supposed to run all the time. While it's normal for auxiliary heat to kick in during exceedingly cold temperatures, running it too long may indicate an issue with the heat pump.

Does Honeywell thermostat automatically switch heat and cool?

The Lyric T6 Pro thermostats has auto-changeover. This allows the thermostat to change between heating and cooling as needed based on the room temperature and the heating and cooling set points. If your thermostat does not show "auto" as one of the options, it has not been configured for auto-changeover.

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