Auxiliary heat and emergency heat for Cincinnati-area heat pumps
If your thermostat shows AUX or Em Heat, the system is using backup heat. That backup is usually electric heat strips in the air handler, or a gas furnace on a dual-fuel system. Geiler services both setups across Cincinnati, Northern Kentucky, and Southeastern Indiana.
Auxiliary heat turns on by itself. The heat pump keeps running, and the backup adds heat when the outdoor unit cannot hold the setpoint alone. That is common on cold nights, after a big setback, or during a defrost cycle. A short AUX display in winter is normal. AUX that stays on all day, or that runs in mild weather, is not.
Emergency heat is a manual setting. It shuts the heat pump off and heats only with the backup source. Use it if the outdoor unit has failed and you need heat until a technician arrives. Do not leave it on for everyday heating. On an all-electric system, emergency heat is the most expensive way to heat the house.
| Setting |
Who turns it on |
Heat pump |
When to use it |
| Auxiliary (AUX) |
Thermostat, automatically |
Stays on and shares the load |
Cold weather, recovery from a setback, defrost |
| Emergency (Em Heat) |
You, manually |
Locked out |
Heat pump failure only |
Call Geiler if AUX runs constantly, the house never reaches the setpoint, or you had to switch to emergency heat to stay warm.
Defrost and dual-fuel
Heat pump defrost: steam, a pause, then heat again
In cold, damp weather, moisture can frost the outdoor coil. Frost blocks airflow, so the heat pump starts a defrost cycle. It briefly reverses, sends warm refrigerant to the outdoor coil, and usually stops the outdoor fan. You may see steam, hear a different sound, or feel cooler air for a few minutes. Auxiliary heat often comes on indoors so the vents do not blow cold air the whole time.
A normal defrost lasts a few minutes, typically under 15, then the system returns to heating. Call for service if the outdoor unit ices over and stays iced, defrosts over and over, or the house gets cold every time it defrosts. Those are repair issues, not a normal winter cycle.
Dual-fuel heat pumps: heat pump plus gas furnace
A dual-fuel system pairs an electric heat pump with a gas furnace. The heat pump handles mild and moderate weather. When outdoor temperature drops to the balance point set for your home, the heat pump shuts off and the furnace carries the full load. When it warms up, the heat pump takes over again.
That switch is different from electric auxiliary heat. Electric strips can run with the heat pump. A gas furnace on a dual-fuel system does not. The changeover temperature should match the equipment, the house, and local utility rates. A setting that is too high runs the furnace more than it needs to. A setting that is too low leaves the heat pump struggling on the coldest Cincinnati and Northern Kentucky nights.
Geiler installs, services, and repairs dual-fuel systems, including thermostat lockouts, furnace changeover, and heat pump controls.
When to call
Schedule heat pump service if you notice any of these:
- AUX or emergency heat is on and the house is still cold.
- Emergency heat was the only way to get heat overnight.
- The outdoor unit is a solid block of ice, or it steams and never returns to heating.
- The furnace and heat pump seem to fight each other, short-cycle, or never switch.
- Heating bills jumped after a cold snap and AUX has been on for days.
Request heat pump service. Tell us whether the thermostat shows AUX or Em Heat, what the outdoor unit is doing, and whether you have electric backup or a gas furnace. We repair, service, and install heat pumps throughout Cincinnati, Northern Kentucky, and Southeastern Indiana, including 24/7 emergency calls.
