HVAC ANSWERS · EQUIPMENT AND EFFICIENCY
Auxiliary and emergency heat
Residential guidance with direct answers, useful observations, and clear next steps.
Updated
Quick answer
Auxiliary heat is supplemental heat that controls may use when the heat pump alone cannot meet the current demand or during certain operating conditions. Emergency heat is typically a manual mode that bypasses normal heat-pump heating. Occasional auxiliary operation can be normal; frequent or unexplained operation should be evaluated with thermostat setup, outdoor conditions, equipment performance, controls, and the building load in mind.
Understand the issue
Auxiliary heat supplements the heat pump under defined conditions; emergency heat is generally a selected operating mode used when the primary heat-pump function is unavailable. The exact sequence depends on the thermostat, equipment, and backup type.
Your questions, answered
Why is AUX heat showing on my thermostat?
AUX usually means supplemental heat has been requested. It may occur during cold conditions, defrost, or recovery from a setback. Persistent unexpected use warrants checking settings, controls, and heat-pump performance.
What is emergency heat?
Emergency heat generally uses the backup heat source while disabling normal compressor heating, depending on the system. Follow the installed equipment's instructions and use it for the intended situation rather than as a routine shortcut.
Should auxiliary heat run with a heat pump?
It can operate alongside the heat pump when the designed controls call for additional output. The expected sequence depends on the system; frequent operation in mild weather may signal a setting or performance problem.
Why are the heat strips coming on?
Electric heat strips may be called by outdoor-temperature conditions, thermostat staging, recovery demands, or defrost. Report when they operate and whether the compressor is working rather than disabling them yourself.
Is backup heat expensive to operate?
Electric resistance backup often costs more per unit of delivered heat than an efficiently operating heat pump. Actual cost depends on energy prices, equipment performance, runtime, and whether the backup is electric or fuel-fired.
What to do next
When to get help
Do not disconnect heat strips or alter staging wiring to reduce bills. Have a qualified technician verify the intended sequence and any underlying loss of heat-pump capacity.
Sources and further reading
These references support the topic's technical background. For equipment-specific procedures, use the instructions for the exact model; for permits and compliance, check with the responsible local authority.
Educational guidance from HVACentric. Conditions at a property require direct assessment; these pages do not diagnose equipment or certify an installation.