Auxiliary / Emergency Heat Running Constantly (High Electric Bill)
The 'AUX HEAT' or 'EM HEAT' indicator on your thermostat stays on for hours at a time, resulting in massive electric bills (often $400-$700+) during Texas winter months.
Identifiable Failure Symptoms
- Thermostat display shows 'AUX HEAT' or 'EM HEAT' almost 24/7
- Monthly electric bill spikes by 200% to 300% during December and January
- Outdoor heat pump compressor is not running or is covered in ice
- Air from vents feels extremely hot and dry instead of gentle warmth
Primary Root Mechanical Causes
- Raising the thermostat setpoint more than 2°F at once (automatically triggers AUX heat)
- Outdoor heat pump compressor broken or locked out, forcing 100% reliance on heat strips
- Stuck electric heat sequencer relay keeping heat strips energized 24/7
- Extreme freezing weather below the heat pump balance point
Initial Safe Verification Steps
Perform these non-invasive safety checks before requesting an on-site technician.
Do Not Bump Thermostats Up by More Than 1-2°F
If the house is 68°F and you want 72°F, raise the thermostat to 69°F first. Once reached, raise it to 70°F.
Verify the Outdoor Heat Pump Is Actually Running
Walk outside. When AUX heat is active, the outdoor compressor should still be running. Is it completely dead?
Check Thermostat Mode Is Set to 'HEAT', Not 'EM HEAT'
Ensure your thermostat mode switch says 'HEAT'. 'EMERGENCY HEAT' forces the system to ignore the efficient heat pump completely.
Safety Protocol — When to Stop DIY
If both the outdoor unit and indoor unit shut off but your electric meter continues spinning wildly, a heat strip sequencer relay is stuck closed, drawing 10,000 Watts continuously.
Ascend Professional Repair Protocol
What our licensed technician tests upon dispatch:
- Electric heat sequencer relay and contactor voltage drop test
- Heat pump heating-mode capacity and compressor amp draw test
- Smart thermostat auxiliary heat lockout temperature programming (e.g. 35°F lockout)
- Outdoor temperature sensor calibration
North Texas Climate & Equipment Reality
In Texas, electric auxiliary heat strips consume 10 to 20 Kilowatts per hour. Running heat strips continuously costs approximately $1.50 to $2.50 per hour in electricity, driving electric bills to astronomical heights.
Expert Mechanical Insights
Why does my electric bill triple when AUX heat runs?
A heat pump delivers roughly 3 to 4 units of heat for every 1 unit of electricity (300-400% efficiency). Electric heat strips deliver a 1:1 ratio. Running strips is 300% more expensive than running the heat pump.
At what outdoor temperature should auxiliary heat turn on in Texas?
In North Texas, a properly sized heat pump can handle 100% of heating down to about 32°F-35°F. Below that 'thermal balance point', auxiliary heat cycles on to supplement the system.
Can I set an outdoor lockout temperature on my smart thermostat?
Yes! Modern thermostats (Ecobee, Nest Pro) allow setting an 'Aux Heat Lockout' at 35°F or 40°F, preventing heat strips from turning on during mild chilly weather.
Related Resolution Blueprints:
Burning Smell When Turning On Heating (Normal vs Hazard)
Heat Pump Blowing Cold Air in Winter
Heat Pump Covered in Ice: Normal Defrost vs Malfunction
Resolve This Issue Today
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