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Visual representation of auxiliary heat
HVAC
Updated August 5, 2025
Auxiliary heat
Auxiliary heat kicks in when your main heating system can't keep up, giving you extra warmth during freezing weather. It’s like a backup heater for extra-cold days.
Category
HVAC
Use Case
Provides supplemental heating when the primary heat source is insufficient in cold weather.
Variants
Electric, Gas, Heat Pump
Key Features
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Supplemental heating for cold weather
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Boosts primary heat pump efficiency
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Activates when temperatures drop significantly
In Simple Terms
What it is
Auxiliary heat is like a backup heater for your home’s heating system. Imagine your main heater is a cozy blanket, but when it gets too cold, you need an extra sweater to stay warm. Auxiliary heat kicks in when your main heater can’t keep up, usually during freezing weather. It’s often part of a heat pump system, which is efficient but struggles in extreme cold.
Why people use it
People rely on auxiliary heat to stay comfortable when temperatures drop suddenly or the main heater isn’t enough. Without it, your home might feel chilly, and your heating system would work harder, potentially costing more in energy bills. Auxiliary heat acts like a safety net, ensuring warmth even when the weather surprises you.
Basic examples
Winter storms: If a cold snap hits and your heat pump can’t warm your home fast enough, auxiliary heat turns on automatically to help.
Early mornings: When temperatures dip overnight, auxiliary heat might run briefly to boost warmth until the sun comes up.
Power outages: Some systems switch to auxiliary heat (like electric coils) if the main heating fuel (e.g., gas) isn’t available.
Think of it like a car’s defroster: your heater warms the car, but the defroster gives extra help to clear icy windows. Auxiliary heat does the same for your home—extra help when you need it most.
Auxiliary heat is like a backup heater for your home’s heating system. Imagine your main heater is a cozy blanket, but when it gets too cold, you need an extra sweater to stay warm. Auxiliary heat kicks in when your main heater can’t keep up, usually during freezing weather. It’s often part of a heat pump system, which is efficient but struggles in extreme cold.
Why people use it
People rely on auxiliary heat to stay comfortable when temperatures drop suddenly or the main heater isn’t enough. Without it, your home might feel chilly, and your heating system would work harder, potentially costing more in energy bills. Auxiliary heat acts like a safety net, ensuring warmth even when the weather surprises you.
Basic examples
Think of it like a car’s defroster: your heater warms the car, but the defroster gives extra help to clear icy windows. Auxiliary heat does the same for your home—extra help when you need it most.
Technical Details
What It Is
Auxiliary heat, also called "aux heat," is a secondary heating system in heat pumps designed to supplement primary heating when outdoor temperatures drop too low for the heat pump to operate efficiently. It falls under the category of backup or emergency heating systems and is typically powered by electric resistance heating strips or a gas furnace.
How It Works
Auxiliary heat activates automatically when the heat pump cannot extract sufficient heat from the outside air due to extreme cold (usually below 35–40°F). The system switches to electric heating coils or an alternative fuel source to generate additional warmth. Modern thermostats often display an "AUX" or "EMER" indicator when this mode is active.
The transition is managed by the thermostat, which monitors indoor temperatures and system performance. If the heat pump cannot meet the set temperature within a specified time, the thermostat engages auxiliary heat to compensate.