Use your emergency heat only in short, true “backup” situations, not just because it’s really cold outside.

What “emergency heat” really is

  • On a heat-pump system, the emergency setting switches off the outdoor heat pump and runs backup heat (usually electric heat strips or a gas/oil furnace) by itself.
  • This backup heat is usually much less efficient and can easily double or more your heating costs if left on for days.

When you should use emergency heat

Use the emergency heat setting when something is wrong with the heat pump or outdoor unit, such as:

  • The outdoor unit is not running , shorting out, or clearly broken (loud grinding, smoke, visible damage, or tripped breaker that will not reset).
  • The outdoor unit is encased in ice or frozen solid and will not defrost, even after multiple normal defrost cycles.
  • A storm, falling branch, or impact has physically damaged the outside unit, bent fan blades, or crushed the cabinet.
  • The system blows only cold air in normal “Heat” mode and you strongly suspect a malfunction, but you still need heat until a technician arrives.

In those cases:

  1. Switch the thermostat to EM Heat / Emergency Heat.
  2. Set the temperature to a modest level (for example, 68–70°F / 20–21°C).
  3. Call an HVAC technician as soon as possible and only use emergency heat until the system is checked.

When you should not use emergency heat

Avoid turning on the emergency setting just because it’s below freezing or very cold outside.

  • Modern heat pumps are designed to run in freezing weather and will automatically use auxiliary heat as needed without you touching “EM Heat”.
  • Manually choosing emergency heat in normal cold weather usually gives little or no comfort improvement but can cause a huge power bill.

Do not use emergency heat as:

  • An everyday winter mode.
  • A way to “heat faster” when the house feels chilly.
  • A workaround for an electrical issue (like a past panel or wiring problem); those must be corrected by an electrician or HVAC pro.

Signs you may need service, not emergency heat

Call a pro (and then use emergency heat if you have no heat) if:

  • The thermostat is set to Heat, but indoor temperature keeps falling and vents stay cool or slightly warm at best.
  • The outdoor unit frequently trips the breaker or won’t start at all.
  • There is loud metallic noise, burning smells, or visible smoke.
  • The outdoor unit is iced over and never seems to clear during defrost cycles.

Simple rule of thumb

  • Normal cold weather, system running, house staying warm: leave it on regular Heat; let the system handle auxiliary heat automatically.
  • Something is broken, iced solid, or clearly unsafe: switch to emergency heat to stay warm and schedule professional service, then switch back to normal Heat as soon as repairs are done.

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