What Does 'Emergency Heat' on a Thermostat Mean? (And When to Use It)
If your thermostat has an EM HEAT or Emergency Heat setting, you have a heat pump. That setting is the one people flip on when the house is cold and they're not sure what else to do — and then leave on for a month while the electric bill climbs. Here's what it actually is.
Safety first, every page: if you smell gas anywhere in the house, leave and call your gas company from outside.
What a heat pump does normally
A heat pump pulls heat from outdoor air and moves it inside — efficient, even when it's cold out. On very cold days, or while the outdoor unit defrosts, it gets a boost from auxiliary heat: electric heating strips in the indoor unit that kick in automatically. You'll see "AUX" or "Aux Heat" on the thermostat when that's happening. That's normal and automatic.
What Emergency Heat does
EM HEAT turns the heat pump off entirely and runs the house on the electric strips alone. Every bit of heat comes from resistance heating — like a giant space heater. It works, and it's the most expensive way to heat a house, often 2–3× the cost of the heat pump.
It exists for one reason: when the heat pump itself has failed and you need heat while you wait for the repair.
When to use it
- The outdoor unit is dead — no fan, no sound, a solid block of ice — and the house is getting cold.
- A technician told you to use it until they can come.
When NOT to use it
- Because it's cold outside. The heat pump handles that with AUX heat on its own. Switching to EM HEAT just makes it cost more.
- Because the air from the vents feels cool. Heat pump air is lukewarm by design (often 85–95°F). If the house holds temperature, it's working.
- Because someone set it last winter. Check now: if EM HEAT is on and the outdoor unit is fine, switch back to HEAT. That alone may be why your bill jumped.
If you find it set to EM HEAT
Switch to HEAT and watch: does the outdoor unit start within a few minutes and does the house hold temperature over an hour? If yes, the heat pump was fine and EM HEAT was just costing you. If the house drops and the outdoor unit never runs, the heat pump has a problem — see heat pump not heating — and EM HEAT is the right stopgap while you call.
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