It's a cold January morning in the Carolinas, you glance at your thermostat, and there it is: "AUX HEAT." If you've ever wondered what auxiliary heat is — and whether you should worry when it's on — here's the plain-English explanation.
Auxiliary heat is your heat pump's built-in backup. A heat pump warms your home by pulling heat from the outdoor air, and it does that brilliantly in our mild North Carolina winters. But when temperatures drop into the 20s and low 30s, there's less heat in the air to grab, and the heat pump alone can't always keep up. That's when your system automatically energizes its backup — usually electric heat strips inside the air handler — to close the gap. That backup is auxiliary heat.
When aux heat is normal: during cold snaps (roughly below 35–40°F), during the defrost cycle when the outdoor unit clears frost off itself, and when you raise the thermostat several degrees at once — the system calls in the strips to catch up quickly. In all of these cases, aux heat cycles on briefly and shuts back off. That's the design working as intended.
When it's a red flag: electric heat strips are honest but expensive — often two to three times the cost of heat-pump heat per hour. If aux heat runs constantly, runs in mild weather (45°F and up), or your winter power bill suddenly spikes, something's usually wrong: low refrigerant, a failing outdoor unit, an iced-over coil, or a thermostat setting driving the strips unnecessarily. One easy habit that helps: raise the temperature gradually (a degree or two at a time) instead of big jumps, and avoid big nightly setbacks in the coldest weeks.
Aux heat vs. emergency heat, one more time: auxiliary heat is automatic — the heat pump and strips work together. Emergency (EM) heat is a manual switch that runs strips only, meant for when the heat pump itself is broken. You never need to flip EM heat just because it's cold.
If your aux heat seems to run more than it should, don't just eat the power bill. Reinhardt Heating and Air can test your heat pump's performance and get it carrying the load again — serving Lincoln, Gaston, Mecklenburg, and Catawba counties, 7am to midnight.