TL;DR
Auxiliary heat is the supplemental heat source, usually electric resistance strips in the air handler, that a heat pump system energizes when the outdoor unit alone cannot hold the thermostat setpoint, typically in deep cold or during defrost cycles. It costs two to three times more per delivered BTU than the compressor, so the goal of good design is to use it rarely.
What it means
Auxiliary heat is the supplemental heat source, usually electric resistance strips in the air handler, that a heat pump system energizes when the outdoor unit alone cannot hold the thermostat setpoint, typically in deep cold or during defrost cycles. It costs two to three times more per delivered BTU than the compressor, so the goal of good design is to use it rarely. The thermostat shows AUX or EM HEAT when it runs; constant display in mild weather signals a refrigerant, sizing, or control problem. Dual-fuel systems use a gas furnace in this role instead of strips.
Where it sits in the glossary
Auxiliary heat is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
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