Quick answer: AUX on a heat pump thermostat means the controls have called for backup heat to help the heat pump, which is often normal on cold Las Vegas mornings or after a big temperature setback. Emergency heat (EM HEAT) is a manual setting that shuts off normal heat pump heating and runs only the backup heat, so it is not a faster way to warm the house. If AUX stays on for hours or the house can’t reach its setting, have the system checked.
Seeing AUX on a thermostat can be surprising when you thought your heat pump was already heating. It usually means the controls have called for supplemental heat. It does not, by itself, prove that the system has failed. Emergency heat is a different control choice, and the details depend on your installed equipment.
AUX is generally automatic
A heat pump moves heat into the home. Some installations also have backup heat that the controls can call when needed. Outdoor conditions, a recovery from a lower thermostat setting and certain operating sequences can influence its use. Not every heat pump has the same backup arrangement.
Record whether AUX appears briefly or stays on, the outdoor conditions and whether the home reaches the setpoint. A new pattern of extended backup operation deserves service, especially if comfort has declined.
Emergency heat is not a “warm up faster” button
On many systems, selecting emergency heat stops normal heat-pump heating and relies on the backup source. It is intended for particular situations described in the equipment instructions or by your technician. Do not select it simply because the vent air feels less hot than air from a gas furnace.
If your heat pump is malfunctioning, call for guidance about your particular setup. Do not assume that a thermostat displaying the option proves that the backup equipment is installed or operating correctly.
Large temperature changes can affect backup use
Some controls bring on electric resistance heat when recovering from a large temperature setback. A heat-pump-compatible thermostat and appropriate configuration can manage that behavior. Avoid experimenting with installer menus or disabling backup heat to lower a bill; those settings may affect comfort and equipment protection.
Ask us to explain the normal daily settings and recovery strategy for your model. The right answer depends on the thermostat, heat pump and backup system together.
What to report
- The exact display: AUX, EM HEAT or another message.
- Whether you changed the operating mode.
- The room temperature compared with the requested temperature.
- Whether the outdoor unit appears to run, observed from a safe location.
These observations help us distinguish a control setting from an equipment problem. They do not require opening a cabinet or checking electrical components.
Background on backup electric heat and controls: U.S. Department of Energy heat-pump guidance.
What this looks like in Las Vegas homes
Most Las Vegas winter days are mild, but clear desert nights can drop into the 30s, especially in Summerlin, Centennial Hills and other higher-elevation neighborhoods on the west side of the valley. That pattern means many heat pumps here run easily all afternoon, then lean on backup heat for a short time around sunrise. Seeing AUX for a few minutes on a cold morning is usually part of that rhythm. Seeing it most of the day on a 55-degree afternoon is not.
Many Las Vegas homes also use a heat pump with electric strip heat as the backup, so heavy AUX use can show up on the electric bill before anyone notices a comfort problem. If your bill jumps in December or January while the weather has been ordinary, that is a good reason to ask for a check. We provide heat pump repair in Summerlin and across the valley, and we can walk you through what normal AUX behavior looks like for your specific thermostat.
Frequently asked questions
Is it normal for my heat pump to show AUX heat in Las Vegas?
Yes, often. Short periods of AUX on cold mornings or after you raise the thermostat several degrees are common. AUX that stays on for long stretches in mild weather is worth a service call.
Should I switch to emergency heat when it gets cold?
Usually not. Emergency heat turns off normal heat pump heating and runs only the backup heat, which can cost more to run. Use it only when your technician or equipment instructions call for it.
Why is my electric bill higher when AUX is on?
On many Las Vegas heat pumps, the backup is electric resistance heat, which uses more electricity than the heat pump itself for the same warmth. Frequent AUX use can raise the bill.
What should I tell the technician about AUX or EM HEAT?
Tell us exactly what the thermostat shows, how long AUX stays on, the outdoor conditions, whether you changed the mode and whether the house reaches its setting.
Get a clear answer for your home
32 Degrees AC & Furnace Repair serves residential customers in Las Vegas, Henderson and North Las Vegas. Learn about our heat pump repair, or request a visit. You can also call 702-635-9505. We explain the findings and obtain your approval before repair work. An online request is confirmed when our office contacts you.