Emergency heat on a heat-pump thermostat should be used only when your regular heat pump can’t safely or effectively run, not just because it is very cold outside.

What “emergency heat” actually is

  • On a heat-pump system, emergency heat is the backup heat source (electric heat strips, gas furnace, or oil furnace) running by itself, with the heat pump turned off.
  • It is manually selected on the thermostat (often labeled “EM Heat” or “Emergency”). It will keep running until you switch back to Heat/Auto.

Think of it as a spare tire: it gets you safely through a problem, but you’re not supposed to drive on it all winter.

When you should use emergency heat

Use the emergency heat setting when there is a real problem with the outdoor heat-pump unit or it cannot operate safely:

  • The outdoor unit is clearly damaged (hit by a falling branch, car, ice, etc.).
  • The heat pump will not run at all, is short‑cycling, or the house is getting colder even though the system is “on.”
  • The outdoor unit is heavily iced over and is not defrosting as it normally does.
  • A technician has told you to use EM Heat until repairs are made.

In these cases, emergency heat keeps your home warm while you arrange service and prevents further damage to a struggling or frozen heat pump.

When you should NOT use emergency heat

Avoid turning on EM Heat just because it feels very cold outside or you want “extra” heat:

  • Normal “Heat” mode (with auxiliary/secondary heat that kicks in automatically) is usually enough, even in freezing weather.
  • Manually switching to EM Heat for routine cold days bypasses the efficient heat pump and forces the system to run the expensive backup heat 100% of the time.
  • Running EM Heat for days or weeks can lead to very high energy bills and additional wear on the backup components.

If your home is a bit cool but the heat pump is working, increase the thermostat a couple of degrees and give the system time—don’t jump straight to EM Heat.

How long can you run emergency heat?

  • Emergency heat is meant for short-term use: just long enough to keep the house safe and comfortable until a repair can be made.
  • Most guides recommend calling an HVAC tech as soon as you turn EM Heat on, then turning it off and going back to regular Heat mode once the problem is fixed.

A simple rule of thumb: if you’ve needed EM Heat for more than a day, you almost certainly need professional service.

Quick Q&A: “when should emergency heat be used?”

  • Use it: When the heat pump is broken, unsafe to run, or badly iced over and not defrosting.
  • Don’t use it: Just because it’s very cold, you want faster heating, or you think “emergency heat” is a turbo setting.
  • Always: Call an HVAC professional if you need EM Heat to stay warm; it’s a warning sign that something is wrong with your normal system.

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