At what temperature should you put your furnace on emergency heat?

Author: Zoey Mosciski I  |  Last update: Wednesday, August 6, 2025

However, what happens when it is too cold outside for the air to be pulled in and heated normally? This is where emergency heat comes in. Typically, this setting on your thermostat kicks on when the temperature is anywhere between 30 to 35 degrees Fahrenheit.

What temperature should I switch to emergency heat?

The Emergency Heat or Auxiliary Heat setting is the second stage of your heating system that is used when the temperature is too low for the heat pump to be able to remove heat from outside, typically below 35 degrees Fahrenheit.

At what temperature is it too cold for a heat pump to work?

Heat Pumps Don't Actually Stop Working

Contrary to popular belief, heat pumps don't ever stop working when it's cold. These systems are built to withstand frigid weather, operating at 100% efficiency even down to -13 degrees Fahrenheit.

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

Homeowners should expect auxiliary heat to turn on during colder temperatures, especially under 40 degrees. Your heat pump is an amazing appliance that can efficiently extract warmth from the outdoor air and transform it into cozy comfort inside your home.

At what low temperature do heat pumps become ineffective?

Heat pumps do not operate as efficiently when temperatures drop to between 25 and 40 degrees Fahrenheit for most systems. A heat pump works best when the temperature is above 40. Once outdoor temperatures drop to 40 degrees, heat pumps start losing efficiency, and they consume more energy to do their jobs.

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

At what temperature should you switch from heat pump to furnace?

With a typical operation of a hybrid heating system, the heat pump will operate with ambient temperatures above 32 degrees. When temperatures are below 32 degrees, the gas furnace will operate.

Will my heat pump automatically switch to emergency heat?

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.

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.

What is the difference between auxiliary heat and emergency heat?

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.

At what temperature does a heat pump stop being efficient?

For this reason, heat pumps start to lose efficiency at around 40 degrees F and become less efficient than furnaces at around 25 degrees F. Heat pumps continue to be effective at cooling the indoors, even at high temperatures. In the South, it rarely gets below 25 degrees.

Should I leave my heat pump on 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 drawback of emergency heat?

Not only is this more expensive, but it is also harder on your HVAC unit—since emergency heat is only meant to run until the problem with your HVAC unit is resolved.

What temperature air should a heat pump put out?

Heat pumps usually produce air that is 85-92°F. This is plenty warm to heat your home to your desired 72°F. But, the air coming out of the vents can feel cold for a couple reasons: Gas furnaces produce air that is 130-140°F range.

Is it OK to run furnace on emergency heat?

Should I Switch My Thermostat to “Emergency Heat” If It's Super Cold Outside? 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.

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 is considered a heat emergency?

Heat emergencies are of three types heat cramps (caused by loss of salt), heat exhaustion (caused by dehydration) and heat stroke (shock). Remove the victim from the heat and have him lie down. Apply cool compresses, elevate the feet, drink fluids and use a fan to blow cool air. Get medical help if needed.

At what temperature should auxiliary heat come on?

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 you turn on emergency heat during an ice storm?

The emergency heat should only be turned on by the homeowner in emergency situations when something happens to the first stage heat source – your heat pump. For example, if during an ice storm a tree is knocked down and damages your outdoor unit, you should switch on your emergency heat and call an HVAC professional.

What is the emergency heat setting on a thermostat?

Setting the thermostat to Emergency Heat tells the system to completely bypass the heat pump. This fires up the auxiliary part of the unit and keeps the house warm until you can get the system repaired. It cuts off signals to the heat pump so that the electric or gas components remain on.

How long can I run emergency heat in my house?

Your system can technically run in Emergency Heat mode indefinitely. Whether your backup heat source is electric or fossil fuel, it's designed for continuous operation without causing damage.

How long should it take to heat a house at 2 degrees?

So how fast should a furnace heat a house? On average, once you turn on your furnace, it should take about an hour to increase indoor temperature by 1 degree. Afterwards, it's 45 minutes per degree.

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.

When should you turn your emergency heat on in winter?

The emergency heat setting usually kicks in automatically when the outdoor temperature drops to between 30℉ and 35℉. However, you can turn it on manually, as we've mentioned, in cases such as: The outside temperature is so cold your home won't warm up. Your heat pump shuts down in extreme cold or during an ice storm.

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.

Why does my thermostat keep switching to emergency heat?

More often than not, the emergency heat is coming on because the temperature in the home is set too high. You are asking your HVAC system to work too hard to maintain a stable temperature. Setting the thermostat for somewhere between 62-68 degrees is all you should need to do to get the situation under control.

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