You should only turn on emergency heat when your heat pump can’t run properly or has failed, not just because it’s very cold outside.

Quick Scoop: When to Use Emergency Heat

Use the emergency heat setting in situations like:

  1. Heat pump is broken or won’t turn on
    • Outdoor unit not running, making loud grinding/banging noises, or clearly damaged (for example, something fell on it).
    • House is getting colder even though the thermostat is calling for heat.
  2. Heat pump is severely iced over or frozen and not defrosting
    • A light frost is normal in winter, but a solid block of ice around the unit, fan blades, or coils is not.
    • If it won’t clear after a defrost cycle and the home is getting cold, you can switch to emergency heat while waiting for a technician.
  3. You’ve been told by a technician to use backup heat
    • If an HVAC tech says “Use EM heat until we can fix the pump,” that’s exactly what this mode is for.
  4. You need temporary heat while waiting for repair
    • Emergency heat keeps the home livable for a short period while the main system is down.
    • It’s essentially using electric strips or a furnace by themselves, which is why it’s expensive to run.

When NOT to Turn On Emergency Heat

Avoid using emergency heat in these situations:

  • It’s just very cold outside (below freezing) but the system still works.
    Modern heat pumps will automatically bring on auxiliary heat when needed; you do not need to flip the switch yourself for “extra warmth.”

  • You want the house to heat up faster.
    Manually turning on emergency heat to “boost” speed is usually unnecessary and can dramatically increase your power bill.

  • You’re just curious.
    Experimenting with emergency heat for long periods can lead to a surprisingly high bill, because it often uses high‑wattage electric resistance heat.

Simple Rules of Thumb

Think of emergency heat as a backup generator, not a “high power” mode:

  • If the outdoor unit is obviously damaged, off, or frozen solid, and your home is getting cold → it’s reasonable to turn on emergency heat and call for service.
  • If the system is running and the house is more or less maintaining temperature (even if it’s working hard) → leave it in normal heat mode and let the thermostat manage auxiliary heat automatically.
  • Once the heat pump is fixed → switch the thermostat back to regular Heat and turn off Emergency Heat.

Mini FAQ

Does emergency heat cost more?
Yes. It typically uses electric resistance heat or a backup furnace by itself, which is much less efficient than the heat pump’s normal operation. Will my house get warmer with emergency heat?
It may feel like it heats faster, but in a properly sized and working system, you shouldn’t need it for everyday cold weather. If you do, it’s a sign that the system may need to be evaluated. Is emergency heat bad for my system?
It’s not “bad” if used as intended—short‑term, during a malfunction. The main downside is cost, not damage.

Example Scenario

You wake up and it’s 20°F outside. The thermostat is set to 70°F, but the house is 63°F and dropping. You check outside and see the heat pump is covered in thick ice and the fan isn’t spinning. In that case:

  1. Turn the thermostat to Emergency Heat to keep the home safe and reasonably warm.
  2. Call an HVAC technician to inspect and repair the heat pump.
  3. After repair, switch back to regular Heat and stop using emergency mode.

If you tell me what type of system and thermostat you have (brand/model, or a photo) and what’s happening at your house right now, I can walk you through whether emergency heat makes sense in your specific situation.