What is the difference between EM HEAT and AUX heat?
AUX heat comes on automatically, working alongside the heat pump when the house needs extra warmth. EM HEAT is something you select by hand, and it locks out the heat pump so only the backup source heats the home until you switch it off.
You normally never touch AUX, because the thermostat manages it. Seeing AUX light up during a cold snap is typical, but seeing it all the time in mild weather is a sign to have the system checked.
The labels vary. Some thermostats say EMER or EMERGENCY, and some smart models hide the setting in a menu. Look at the manual if yours does not show it.
On most thermostats the AUX light turns on by itself, while EM HEAT needs a button press or menu choice. If you see AUX on a very cold morning, that is the system working as designed. If EM HEAT is on, the heat pump is being skipped entirely.
Why is EM HEAT on when I did not select it?
EM HEAT may show on a thermostat if someone changed the mode by accident, if the thermostat is set up incorrectly, or if the system has detected a fault in the heat pump. Check the mode setting first, then call a technician if it returns.
Smart thermostats sometimes switch to backup heat when they detect the outdoor unit is not responding. Look at the outdoor unit. If the fan is not running and the unit is silent, the heat pump may be down.
Also confirm the thermostat is configured for a heat pump. A wrong setup can make the display behave strangely and trigger backup heat when it should not.
Check the thermostat for a recent change, since children or guests sometimes press buttons. If the setting keeps coming back after you reset it, take a photo of the display and the outdoor unit and call. It helps a technician narrow down the cause quickly.
Does emergency heat cost more to run?
Yes. Emergency heat usually costs more to run than normal heat pump heating because electric heat strips use much more electricity to make the same amount of warmth. That is why it should be a short term fix while the heat pump gets repaired.
A heat pump moves heat, while heat strips create it directly. The difference shows up on the electric bill if the setting is left on for days.
If your house is using backup heat for long stretches and you did not choose it, you may be paying extra without noticing. A technician can find out why.
Electric heat strips are simple and reliable, but they convert electricity directly to heat, so they cannot match what a working heat pump does. In a mild West Valley winter, using emergency heat for long stretches wastes money without making the house much warmer.
What should you do if your heat pump fails in winter?
If your heat pump stops heating, check the thermostat mode, the filter and the breaker, then switch to EM HEAT only for temporary warmth while you arrange a repair. Do not leave it on for days, and shut the system off if you smell burning.
Look at the outdoor unit for heavy ice or a silent fan, and listen for the compressor. Report what you see when you call, as it speeds up the diagnosis.
Vortech repairs heat pumps and installs thermostats across Glendale, Peoria, Sun City, Sun City West and Surprise. Use the call button on this page to set up a visit.
Never block vents or close off registers to push heat to one room, and keep the filter clean. If you smell burning when backup heat first starts after a long idle, that can be dust on the elements, but a strong or lasting smell means shut it off and call.
More questions: Thermostats: 12 Most Asked Questions Answered