Heat Pump Auxiliary vs Emergency Heat

Heat Pump Auxiliary/ Back Up Heat vs Emergency Heat are different yet similar settings for your heat pump system. Heat pumps operate with many options to keep you cool in the Summer and warm in the Winter. In the Winter, the heat pump is designed with a booster (auxiliary heat) which automatically enables it to maintain desired temperature when it is otherwise difficult to do.

Emergency Heat Mode is a manual setting which is designed to provide heat when the heat pump cannot, such as a failed component.

Auxiliary Heat Mode is a backup heating system that turns on when your heat pump can’t keep up with the heating needs. It’s completely normal and built into most heat pump systems and provides supplemental heat so your home stays warm even in very cold weather. It also keeps the heat pump from overworking when temperatures drop.

Normal Auxiliary Heat Operation

• The outdoor temperatures are too cold for the heat pump to efficiently pull heat from outside.
• Your system is trying to raise the indoor temperature quickly or during a defrost cycle.
• Outdoor temps drop below 30–35°F
• You raise the thermostat by more than 2–3 degrees at once
• The system is recovering from a setback

If Auxiliary heat comes on briefly and then shuts off, that is considered normal.

Abnormal Auxiliary Heat Operation

If you notice any of these, something may be wrong and you should contact your HVAC Specialist

• Auxiliary heat stays on for long periods, even when outdoor temps are mild (above 35 to 40°F).
• Your electric bill suddenly spikes as compared with prior usage during same conditions. Auxiliary heat uses three to five times more electricity than the heat pump.
• The heat pump runs constantly but can’t reach the set temperature. This can mean Low refrigerant, a Dirty outdoor coil, a Failing compressor or weak airflow.
• Auxiliary heat turns on even for small temperature changes. For example: You raise the thermostat from 70 to 71 degrees and auxiliary heat kicks in.
• Auxiliary heat runs even when the outdoor unit is off which can indicate heat pump failure, the outdoor unit is frozen or thermostat wiring issues.

Things to check if your system is running in Auxiliary Heat Mode

1. Check the outdoor temperature,
   • If it’s below freezing, Auxiliary heat is expected.
   • If it’s mild and Auxiliary heat is still on, that’s suspicious
2. Listen to the outdoor unit, Is it running?
   • Yes: AUX may just be assisting
   • No: The heat pump may not be working at all
3. Check your thermostat settings. Look for:
   • Large temperature jumps
   • “Emergency Heat” accidentally turned on
   • Smart thermostat schedules that cause big swings
4. Inspect the outdoor unit (visually), check for
   • Ice covering the entire unit
   • Debris blocking airflow
   • Fan not spinning

If the whole unit is encased in ice, you will need to contact a licensed HVAC technician. Read more here

Emergency heat mode is a manual backup mode used only when the heat pump cannot operate or function under normal conditions. It should only be used if

• The outdoor unit is frozen, damaged, or malfunctioning
• You have been instructed by a technician
• The heat pump is awaiting parts or repairs

Emergency Heat Mode is the most expensive heating mode and should only be used temporarily. The cost of running the system in emergency heat mode can be three to five times more expensive than normal.

If your heat pump system runs all the time, operates abnormally in auxiliary heat mode or you are unsure about high electric bills, Contact Air Doctor Heating and Air for service. Call or text us at 301-799-7200