Emergency heat, aux heat, and what your thermostat is telling you

Both terms point at the same hardware: your backup heat source, which in most KC installs is electric resistance strip heat inside the air handler (in a dual-fuel system, it's a gas furnace instead). The difference is who's in charge:

• Auxiliary (aux) heat is automatic. When the heat pump can't keep up — a deep cold snap, a defrost cycle, or a big thermostat setback to recover from — the system stages the backup on alongside the heat pump, then drops it as soon as the heat pump can carry the load again. You'll see "aux heat" flash on the thermostat. That's normal operation, not a malfunction.
• Emergency (EM) heat is manual. Flipping that switch locks the heat pump out completely and runs the backup as the only heat source. It exists for one scenario: the heat pump itself is down.

One sentence to remember: aux heat is the system asking for help; EM heat is you firing the heat pump.

In ASHRAE zone 4A, here's the healthy pattern across a winter in Kearney, Grandview, or anywhere else in the metro:

• Aux heat, automatically: expect it during the 10–20 nights a year below about 20°F, briefly during defrost cycles on frosty mornings, and when recovering from a large setback. Minutes to hours at a time, then gone.
• EM heat, manually — only when the heat pump has physically failed: the outdoor unit is dead, iced into a solid block that defrost can't clear, or a tech told you to lock it out until a repair. EM heat is the spare tire: it gets you to the shop, and you don't commute on it.

A smart thermostat configured for your equipment handles the staging well; the classic mistake is cranking the setpoint 5+ degrees at once, which many thermostats read as an emergency and answer with strip heat. Nudge the setpoint instead. How the heat pump side of this works is covered in how a heat pump works in a KC winter.

These three patterns generate more winter high-bill calls than any equipment defect:

1. Running EM heat all winter by choice. Some owners flip EM heat in December because "it feels warmer" (strip heat does blow hotter air) or because they think they're sparing the heat pump. Heat pumps are designed to run in the cold; the strips are not designed to be your furnace. This is the single most expensive mistake a KC heat-pump owner can make.
2. Misconfigured staging that fires strips in mild weather. Wrong thermostat setup — bad balance-point setting, wrong equipment type selected — quietly brings strips on at 40°F when the heat pump alone could coast. Bills climb and nobody knows why.
3. Ignoring what constant aux heat is saying. "Aux heat" glowing steadily at 35–40°F outside is a symptom, not a setting problem: a low refrigerant charge, a failing defrost cycle, or a dying compressor is quietly making the heat pump too weak to carry a mild day. The strips cover it — expensively — until the heat pump finally quits.

No invented numbers needed; the physics does the talking. Electric resistance strips convert one unit of electricity into exactly one unit of heat. A heat pump moves two to three units of heat per unit of electricity through most of a KC winter. Run strips instead of the heat pump and you're paying roughly two to three times as much for every hour of heat, at current Evergy rate structures — and strip heat is the largest electrical load in most houses while it runs.

That's why a January EM-heat month shows up on an Evergy bill as a spike you'll notice, and why the field diagnosis is often instant: a shocking winter electric bill plus a heat-pump home usually means the strips have been carrying the house, whether by switch, by misconfiguration, or by a failing heat pump. In a dual-fuel home the same handoff logic applies with gas as the backup — see when a hybrid makes sense in KC.

Three take-homes:

• Leave the thermostat in normal heat mode and let aux heat stage itself. Brief aux operation in the cold is the system working correctly.
• Reserve EM heat for a physically failed or solidly iced heat pump — and book the repair the same day you flip it, because every hour on strips is the expensive hour.
• Treat "aux heat" showing constantly in mild weather as a service symptom. Something upstream is failing, and catching it early is dramatically cheaper than the strip-heat bills that mask it.

If your thermostat is living on aux heat, or your winter electric bill just told the story for you, get in touch and we'll find out why the heat pump isn't carrying its load — details on our heat pump repair page.