Emergency heat is a backup for when your heat pump has actually failed, not a button to press because the house feels chilly. Auxiliary heat comes on by itself to help the heat pump on a cold Lubbock morning; emergency heat shuts the heat pump off and runs the electric strips or furnace alone, which costs considerably more. If your system is calling for aux or emergency heat constantly, that is a fault to diagnose, not a setting to live with.
What is aux heat, and how is it different from emergency heat?
Aux heat is automatic; emergency heat is you taking over. A heat pump makes heat by moving it from outdoor air into your house, which is cheap and efficient but gets harder as the temperature drops. When the thermostat sees the heat pump alone cannot hold your setpoint, it switches on supplemental heat — electric resistance strips in the air handler, or a gas furnace in a dual-fuel system — and displays AUX HEAT while both run. That is the system working as designed.
EM HEAT is different. Choosing emergency heat locks the compressor out and runs only the backup. The house still gets warm, but you have switched off the efficient half of the equipment. Think of it as the spare tire: fine to get you through, not something to drive on all winter.
When should I actually switch to emergency heat?
Only when the heat pump itself has stopped doing its job. The short list:
- The outdoor unit is not running at all, or is running but the house keeps getting colder.
- The outdoor coil is encased in solid ice and is not clearing after a defrost cycle.
- Something is obviously broken — a loud grinding or screeching from the outdoor unit, or a breaker that trips every time the compressor tries to start.
- A pro has told you to run it that way until they can get out to you.
Notice what is not on that list: cold weather. Lubbock winters dip into the 20s routinely and into the teens when a hard front comes through, and a working heat pump still pulls useful heat out of air that cold. The thermostat brings in backup automatically for those hours. Flipping to emergency heat yourself only removes the efficient half of the system.
One more habit worth breaking: deep thermostat setbacks. Drop the house eight degrees overnight and the morning recovery is a big enough jump that the thermostat calls for aux heat to catch up, often costing more than the setback saved. Our notes on winter thermostat settings for Lubbock homes go into the numbers.
If you had to flip to emergency heat, treat it as a service call, not a fix. Running on backup heat means you are paying resistance-heat prices every hour until the heat pump is repaired. Call (414) 429-5333 and we will connect you with an independent local HVAC pro, or request a callback and we will reach out to you.
Why does my heat pump blow cool air and steam in winter?
That is usually a normal defrost cycle, not a breakdown. Frost collects on the outdoor coil in cold, damp weather and chokes off airflow, so the unit briefly reverses itself to melt the ice — which is why you see steam rolling off the outdoor unit and why your vents can feel cool for a few minutes. Most systems add a little backup heat during defrost to temper that air.
A healthy defrost is short and occasional. What is not healthy is a unit that defrosts every few minutes, stays there a long time, or comes out still covered in ice. That points to a refrigerant charge problem, a failed defrost board or sensor, or a fan not moving air — all of which need a gauge set and a meter, so they belong with a licensed pro.
How much more does emergency heat cost?
Considerably more, and the reason is physics rather than pricing. Electric resistance heat converts one unit of electricity into one unit of heat, full stop. A heat pump does not make heat, it moves heat, so the same electricity delivers roughly two to three times as much warmth depending on the outdoor temperature and the equipment. Swap the heat pump for the strips and you are buying the same comfort at several times the energy input.
What that means in dollars depends on your home, your rate, and the hours it runs — costs vary, and a local pro can estimate it for your house. The practical point is that a heat pump left on EM HEAT for a few weeks is one of the most common causes of a winter bill that makes people call us. If yours has jumped and you cannot explain it, our guide to a high heating bill in Lubbock covers the other usual suspects.
My aux heat runs constantly. What should I check?
Start with the one thing that is safely yours to do: the filter. A clogged filter starves airflow across the indoor coil, the system cannot deliver the heat it is making, and the thermostat keeps calling for backup to compensate. Between caliche dust, spring wind, and cotton harvest, Lubbock filters load up faster than the box suggests — check yours monthly through the season.
Then the obvious: nothing stacked against the outdoor unit, no furniture over the return vents, and the thermostat set to HEAT rather than EM HEAT left over from last winter. People find that switch flipped more often than you would think.
Past that, stop. Constant aux heat with a clean filter usually means low refrigerant charge, a failed reversing valve, a stuck defrost control, or a thermostat miswired for the equipment. Those involve refrigerant handling and live electrical work — licensed-pro territory, and genuinely dangerous to poke at. Get heating service booked instead, and if this is the third winter of problems, ask about replacement equipment while you are at it, since modern heat pumps hold their capacity far lower than units from a decade ago. If something has failed outright and the house is cold now, that is an emergency repair, not a tune-up.
Not sure a heat pump is even the right system for a West Texas house? We compared the options in heat pump vs. furnace in West Texas.
Frequently asked questions
What is the difference between aux heat and emergency heat on my thermostat?
Aux heat is automatic and emergency heat is manual. When the thermostat displays AUX HEAT, the heat pump is still running and the backup heat is helping it keep up. When you switch the system to EM HEAT, you are shutting the heat pump off entirely and running only the backup, which is the most expensive way to heat the house. Aux heat is normal on a cold Lubbock morning. Emergency heat is a setting you choose when the heat pump itself has stopped working.
Should I run emergency heat during a Lubbock cold snap?
No, not just because it is cold outside. A heat pump still produces useful heat well down into the 20s and teens, and the thermostat will bring in backup heat automatically when it needs help. Flipping to emergency heat on a cold night turns off the efficient part of the system and leaves you paying for electric resistance heat you did not need. Save that switch for an actual equipment failure.
Why does my heat pump blow cool air and steam outside in winter?
That is almost certainly a normal defrost cycle. Frost builds on the outdoor coil in cold, damp weather, so the unit briefly reverses itself to melt the ice off, which is why you see steam rolling off the outdoor unit and why the indoor air can feel cool for a few minutes. Most systems bring on a little backup heat during defrost to temper that air. If the cycle runs every few minutes, lasts a long time, or the coil stays iced over, have a pro look at it.
How much more does emergency heat cost to run?
Noticeably more, because electric resistance heat can only turn one unit of electricity into one unit of heat, while a heat pump moves two or three times that much heat for the same electricity. Actual dollars depend on your home, your rate, and how long it runs, so costs vary and a local pro can give you a real estimate. The practical takeaway is that a heat pump left on emergency heat for weeks shows up clearly on a winter bill.
My heat pump runs on aux heat all the time. Is something wrong?
Probably, yes. Constant aux heat usually points to a real fault rather than cold weather: a clogged filter, low refrigerant charge, a failed reversing valve, a stuck defrost control, or a thermostat wired or configured incorrectly. Refrigerant and electrical diagnosis is licensed-pro work, not a do-it-yourself fix. Change the filter, then have an independent local HVAC pro test the system before the bill climbs any further.