Heat Pumps & Mini-Splits
What Is Auxiliary/Backup Heat & Lockout Controls?
Definition
Auxiliary (or backup/emergency) heat is a secondary heat source — usually electric-resistance strip heat, sometimes a gas furnace in a dual-fuel setup — that supplements or replaces the heat pump when outdoor temperatures drop below its efficient range. Lockout controls set the exact outdoor temperature at which that switch happens.
Why it matters for your home
Backup heat is far more expensive to run than the heat pump itself, so a lockout control set too aggressively (switching over too early) can quietly inflate a winter electric bill without you ever seeing an error or a comfort problem.
What to do about it
Ask your installer what outdoor temperature triggers backup heat on your system, and whether that setting matches your equipment's actual cold-weather capacity — not just a generic default.
This definition is pending licensed-trade technical review. It's sourced from our own published service and guide content, not invented — but hasn't yet been signed off by a licensed HVAC reviewer.
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