You should only switch a heat pump to emergency heat when there’s a problem with the heat pump itself and it can’t safely or effectively run, not just because it’s very cold outside.

What “emergency heat” really does

  • On most heat pump thermostats, “EM HEAT” or “Emergency Heat” turns the outdoor heat pump completely off and runs only the backup heat (electric strips or sometimes gas/oil).
  • That backup heat works like a big electric space heater inside your ductwork, which is powerful but much less efficient and far more expensive to run than the normal heat pump mode.
  • Modern heat pumps already switch in backup/second‑stage heat automatically when they need help in very cold weather, so you usually do not need to touch the emergency setting at all.

Think of “emergency heat” as a spare tire: it’s there to get you by when something is wrong, not for everyday driving.

When you should switch to emergency heat

Use the emergency heat setting in situations like:

  1. The outdoor unit is damaged or clearly malfunctioning
    • Tree or branch falls on the unit, obvious physical damage, loud grinding, burning smell, or breaker repeatedly tripping.
 * In this case, turn the thermostat to Emergency Heat and call an HVAC tech, so you stay warm without running a damaged unit.
  1. The outdoor unit is a block of ice or badly iced over
    • A thin frost that comes and goes is normal, but if the unit is encased in ice and not defrosting, that’s a malfunction.
 * Switch to Emergency Heat and shut the pump down until a technician can fix the defrost problem.
  1. The heat pump won’t come on or can’t keep up at all
    • Thermostat is calling for heat, but the outdoor unit never starts, or it starts then immediately shuts off and the house keeps getting colder.
 * Use Emergency Heat as a temporary backup so your home doesn’t drop to unsafe temperatures while you wait for service.
  1. You’re told to by a technician
    • Sometimes an HVAC pro will ask you to leave it on Emergency Heat until they arrive or until a specific repair is done.

When you should not use emergency heat

These common situations usually do not justify flipping to Emergency Heat:

  • It’s just very cold outside (below freezing or even near 0°F / −18°C)
    • Older advice said to manually switch to emergency heat in deep cold, but newer heat pumps are designed to run in low temperatures, and they already bring on backup heat automatically when needed.
  • The system runs a long time or uses AUX heat
    • Seeing “AUX” or “Aux Heat” is normal in cold snaps; that’s your thermostat allowing supplemental heat to help the pump, not full emergency mode.
  • You want the house to “heat up faster”
    • Emergency Heat won’t really speed things up much but will usually spike your electric bill, especially with electric strips.

Cost and energy implications

  • Emergency heat with electric resistance strips can cost several times more per hour than running the normal heat pump cycle.
  • Using it for days as a “comfort booster” instead of for a true emergency can lead to a big, unpleasant surprise on your next bill.
  • Short-term use (a day or two) in a real breakdown is exactly what it’s there for; just switch back to normal heat as soon as the pump is repaired.

Simple rule-of-thumb you can follow

You can think of it this way:

If the heat pump itself is broken, unsafe, iced solid, or obviously not running right, switch to Emergency Heat and call for service.
If it’s just cold outside or the system runs longer than usual but still works, leave it in normal Heat mode and let it manage backup heat automatically.

Mini FAQ and “forum-style” notes

  • “My thermostat’s red emergency light is on—what now?”
    • If you didn’t turn on Emergency Heat, a steady or flashing red light can mean the system detected a problem and shifted to backup heat; it’s a good idea to schedule a checkup.
  • “Is it bad to leave emergency heat on all winter?”
    • It’s not usually dangerous, but it’s very expensive and hides underlying problems that should be fixed.
  • “What if my house still won’t warm up even on emergency heat?”
    • That points to a separate issue (ducts, insulation, heater sizing, or a failed backup heat source), and you’ll need an HVAC pro to diagnose it.

“Emergency heat is like calling in the backup band when your main performer walks off stage—helpful in a pinch, but not who you want playing every show.”

SEO-style quick pointers

  • Main focus phrase: when should you switch to emergency heat on heat pump – Answer: only for a broken, iced, or malfunctioning heat pump, or when instructed by a technician, not just during normal cold weather.
  • Related angle: people online debate this in winter “latest news” and “forum discussion” threads, but modern guidance consistently says Emergency Heat is for actual emergencies and short-term use.

Meta description suggestion:
Homeowners often ask when they should switch to emergency heat on a heat pump. Learn the exact situations it’s truly needed, why it’s so costly, and how modern systems handle extreme cold.

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