What 'EM Heat' actually does
EM heat — short for emergency heat — is a manual override that forces your heat pump to stop and turns on the auxiliary electric heat strips instead. Heat pumps normally reverse the refrigerant cycle to pull heat from outdoor air. In EM heat mode, the compressor shuts off entirely and electricity runs through resistance coils, like a giant space heater in your air handler.
When you should (and should not) use it
The switch exists for genuine emergencies: the outdoor unit is iced over, a defrost board failed, or the heat pump lost its charge and can't pull heat. In those cases EM heat keeps the house warm until a tech arrives. It should almost never be used as a routine 'I feel cold' button — most thermostats do that automatically with 'auxiliary heat' during a normal defrost cycle.
What EM heat costs to run
Resistance heat is roughly two to three times more expensive than heat-pump operation. A typical Houston heat-strip package draws 10 to 15 kW. Running EM heat 24/7 for a week can add $300–$500 to your electric bill versus a working heat pump. If your system runs in EM heat on its own for more than a few hours at a time, that's a fault, not normal behavior.
EM heat stuck on? That's usually a failed component
A thermostat stuck displaying EM heat usually means one of three things: the thermostat itself is miswired or misconfigured, the outdoor unit is tripped or dead so the system fell back to strips, or a defrost control has failed. We check the outdoor disconnect, the capacitor, the reversing valve coil, and the thermostat wiring in that order — most are cheap fixes.
Frequently Asked Questions
Is EM heat more expensive to run?
Yes — roughly two to three times the cost of normal heat-pump heat, because it uses electric resistance strips instead of moving outdoor heat.
Why did my thermostat switch to EM heat by itself?
The system likely caught a fault and fell back to the heat strips, or the thermostat is misconfigured. A heat pump that runs EM heat on its own for hours needs a service call.
Can heat pumps heat a Houston home without EM heat?
Absolutely. Modern heat pumps heat efficiently even in the mild freezes Houston sees. EM heat is a backup, not the primary source.
HVAC247PRO is a licensed Texas HVAC contractor (TACLB00105442E and TACLA95904E) serving the Houston metro 24/7. If your system is showing any of the signs above, call (346) 451-1559 or book an inspection online and a technician will be at your door the same day.