Why Your Heat Pump Runs in "Emergency Heat"

Why Is My Heat Pump Stuck on “Emergency Heat”?

Emergency heat bypasses your heat pump’s normal compressor cycle entirely and runs on electric-resistance backup heat only — the same principle as a space heater, built into the system. It’s designed to kick in briefly during a hard freeze when the compressor can’t keep up, or when you switch it on manually because the outdoor unit has failed. If it’s running for hours at a time in normal weather, that’s a sign something’s wrong, not a sign the system is working as intended.

When Emergency Heat Is Supposed to Run

A properly working heat pump switches to backup heat automatically during the coldest nights of the year, when outdoor temperatures drop low enough that the compressor alone can’t keep up with your home’s heat loss. In the Birmingham Metro, that’s typically a handful of nights each winter — not a routine occurrence.

When It Means the Compressor Has a Problem

If emergency heat is running constantly, even on a mild day, the compressor side of the system likely isn’t working — a failed component, low refrigerant, or a frozen outdoor coil can all force the system into backup-only operation. This isn’t a setting you can fix by adjusting the thermostat; it requires diagnosing why the compressor stopped contributing.

Why It’s Expensive If It’s Stuck

Electric-resistance heat is one of the least efficient ways to heat a home — it’s a direct one-to-one conversion of electricity to heat, without the efficiency multiplier a heat pump’s compressor provides. A system stuck on emergency heat for days or weeks can noticeably raise a power bill compared to normal heat-pump operation, on top of the fact that the underlying problem is still unresolved.

How to Tell the Difference

Most systems show a distinct “Emergency Heat” or “Emerg Heat” indicator on the thermostat when it’s engaged — if that light is on outside of a genuine hard freeze, or your outdoor unit isn’t running at all while it’s on, that’s the signal to call for diagnosis rather than let it run.

Seeing the emergency heat light more than a few nights a year? Schedule a heat pump diagnostic and we’ll find out why the compressor isn’t carrying its share.