You should only switch to emergency heat when your heat pump can’t operate normally or has likely failed, not just because it’s really cold outside.

What “emergency heat” actually is

  • On a heat pump system, emergency heat bypasses the outdoor unit and uses the backup heat source only (usually electric heat strips or a gas furnace).
  • This backup heat is usually much more expensive to run than your normal heat pump operation.
  • Modern heat pumps are designed to work efficiently even in freezing weather, so you generally should not switch to emergency heat just due to low outdoor temperature.

When you should switch to emergency heat

Use the “EM HEAT” or “EMERGENCY HEAT” setting if:

  1. The heat pump is not working or severely struggling
    • Indoor temperature keeps dropping even though the thermostat is calling for heat.
    • You notice the outdoor unit isn’t running at all when it should be.
    • The breaker keeps tripping or the system repeatedly shuts down.
    • In these cases, switching to emergency heat lets the backup heat run while you schedule service.
  1. Physical damage to the outdoor unit
    • Tree limb, ice, debris, or an impact damaged the outdoor unit (bent fan, crushed cabinet, etc.).
    • Turn off regular heat, switch to emergency heat, and call an HVAC tech to avoid further damage.
  1. Severe icing or defrost failure
    • Outdoor unit is encased in ice or heavy freezing rain/ice storm has it frozen over.
    • If the defrost cycle isn’t clearing it and it looks like a solid ice block, you can switch to emergency heat to keep warm and protect the unit while waiting for repair.
  1. Confirmed malfunction from a technician
    • If an HVAC technician tells you to run on emergency heat temporarily until parts arrive or a repair is completed, follow that instruction.

When you should not use emergency heat

Avoid turning on emergency heat in these situations:

  • It’s just very cold outside, but the house is maintaining set temperature (even if the system runs a lot). Modern heat pumps are built for this.
  • You want “extra comfort” or faster heating but the system is working normally. You’ll mostly just get a much higher electric bill.
  • You’re curious and want to “try it out.” Cycling to emergency heat for no reason stresses the system and wastes energy.

Simple rule-of-thumb checklist

Ask yourself:

  1. Is my home still reaching or staying near the set temperature?
    • Yes → Stay on normal heat.
    • No → Go outside and safely look at the heat pump.
  2. Is the outdoor unit clearly damaged, off, or a block of ice?
    • Yes → Switch to emergency heat and call for service.
    • No → Leave it on normal heat and consider a service call if performance seems off.
  3. Am I switching to emergency heat only because it’s below freezing?
    • If that’s the only reason → Don’t switch; this is normal operating territory for many newer systems.

Cost and safety notes

  • Emergency heat often uses high-wattage electric strips, so it can drive your bill up quickly if left on for days.
  • It’s meant as a temporary backup until your heat pump is fixed, not a seasonal mode.
  • If your home won’t stay warm even on emergency heat, or breakers trip repeatedly, shut the system off and call a professional immediately (that’s a safety and comfort issue).

Forum-style quick scoop

Common forum advice right now (winter 2025–2026):

  • Don’t flip to emergency heat just because it’s 20°F or below.
  • Do flip it on if your outdoor unit is dead, smashed, or iced solid.
  • Then call a pro and use emergency heat only until they sort it out.

SEO bits you asked for

  • Focus keyword used: “when should i switch to emergency heat” (answer: only when the heat pump can’t safely or effectively run, like damage, failure, or extreme icing).
  • Related to “latest news” and “forum discussion”: recent HVAC blogs and Q&A threads this season strongly warn against using emergency heat as a routine cold-weather setting due to high costs and improved efficiency of modern heat pumps.

TL;DR: Switch to emergency heat only when the heat pump itself is not working correctly (failure, damage, or severe icing) and use it as a short- term backup while you get the system repaired.

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