You should only switch your heat pump to emergency heat when the heat pump itself is not working correctly or could be damaged if it keeps running.

What “emergency heat” really means

  • A heat pump has two stages: normal heat pump operation (stage 1) and backup heat (stage 2), usually electric resistance strips or another backup heater.
  • Turning the thermostat to Emergency Heat shuts the outdoor unit (heat pump) off and runs only the backup heat source.
  • That backup heat is much less efficient and can make your electric bill jump dramatically.

When you should switch to emergency heat

Use the Emergency Heat setting if:

  1. The heat pump is not heating at all
    • House stays cold even though the thermostat is calling for heat.
 * Supply air feels barely warm or cool, and the system has been running a long time with no improvement.
  1. The outdoor unit is visibly damaged or clearly malfunctioning
    • A tree/branch fell on the outdoor unit, the fan is broken, or the unit is physically crushed.
 * You hear loud grinding, screeching, or other abnormal noises that suggest something is failing; turning on emergency heat lets you shut the outdoor unit down until it’s checked.
  1. The outdoor unit is encased in ice or the defrost system has failed
    • The entire outdoor unit is a solid block of ice or heavily iced over, not just a light frost between defrost cycles.
 * In severe ice storms, temporarily switching to emergency heat can prevent fan and coil damage by keeping the outdoor unit off.

In all of these cases, emergency heat is a temporary safety/comfort mode while you wait for an HVAC technician to diagnose and repair the heat pump.

When you should not use emergency heat

Do not switch to Emergency Heat just because:

  • It’s below freezing or extremely cold outside
    • Modern heat pumps are designed to operate in cold weather, and older “switch at 32°F” advice is considered outdated.
* Aux/backup heat will come on automatically if the thermostat and system are set up correctly; you don’t need to flip the emergency setting yourself for normal cold snaps.
  • You think “emergency heat = stronger or faster heat”
    • It may feel warmer because electric strips run hotter, but they burn far more energy, so using them when the heat pump still works just wastes money.
  • The system is maintaining your set temperature (even if it runs longer)
    • Longer run times in cold weather are normal for heat pumps and often more efficient than cycling a high-wattage backup heater on Emergency Heat.

How most thermostats handle this automatically

On many modern systems:

  • “Heat” mode lets the thermostat decide when to run the heat pump alone and when to add auxiliary heat if the home falls several degrees below setpoint or the call for heat is prolonged.
  • “Emergency Heat” is a manual override that locks out the outdoor unit and forces only the backup heat source to run.

So in everyday winter conditions, you leave the thermostat on Heat , and the system takes care of staging and backup automatically.

Quick forum-style takeaway

If this were a forum thread, the top-voted reply would sound like:

Only use Emergency Heat when the heat pump is broken, iced solid, or could be damaged if it keeps running. It’s not a “cold weather boost” button and will seriously spike your power bill.

Bottom note: Information gathered from public forums or data available on the internet and portrayed here.