You tap Heat on a cold morning in Clairemont and notice a second label: Em Heat, or Emergency. That mode is not a turbo button. It is a manual bypass that shuts the outdoor heat pump off and runs electric backup heat instead.
What the emergency heat setting is for
Emergency heat is a thermostat mode you select on purpose. On most heat-pump controls it tells the indoor unit to warm the house with electric backup heat only. The outdoor unit is taken out of the heating call. That is the whole point of the setting: keep some heat in the house when the heat pump itself cannot run.
You should reach for it only when the outdoor unit is out of the picture. Typical cases are a heat pump that will not start, a unit with obvious damage, or a licensed technician who has already said the compressor side is down and backup heat is the holdover. It is a temporary way to stay warm while a licensed independent pro diagnoses the equipment. It is not a comfort upgrade for a chilly night in Encinitas or a way to get the hallway warmer, faster.
Labels vary by brand. Some wall stats say EM HEAT. Others say Emergency, Em Heat, or bury the choice under a hold or mode menu on a smart thermostat with a heat pump. Mini-split remotes often skip the wording entirely. If your display does not show an emergency-heat option, do not assume the indoor unit has strip heat you can force from the living room. Confirm what your equipment actually has in the installer manual, or have a licensed pro read the indoor board and the thermostat wiring.
Auxiliary heat is the setting people mix this up with. Aux heat (sometimes AUX or Aux) is usually automatic. The control brings electric backup on for a stretch when the heat pump needs help, then lets the outdoor unit keep doing the main work. Emergency heat is the manual override. You choose it. The heat pump stays off until you take the thermostat out of that mode.
If the house is merely slow to catch up after a setback, leave the system in regular Heat. If the outdoor fan is spinning and the air from the registers is only a little cool, that is a service question, not an automatic trip to emergency heat. Flip the mode only when you have a real reason to keep the outdoor unit off.
How it differs from normal heat pump heating
A heat pump heats by moving warmth from outdoor air into the house. Even on a 40-degree night in El Cajon, there is heat in that air to collect. The outdoor unit runs, refrigerant carries the heat indoors, and the air handler or indoor head delivers it. That is normal Heat on the thermostat.
Emergency heat does not collect outdoor heat. It uses electric resistance elements in the indoor equipment, when the system has them. Those elements turn electricity straight into warmth. That is why the mode can still produce heat with the condenser sitting quiet on the pad. It is also why a stretch of emergency heat shows up on an SDG&E bill in a way normal heat-pump heating does not. Heat Pro SD does not publish a multiplier or a dollar figure for that difference. No verified rate belongs on this page. Read your own statement after a period of use, and ask the matched pro what your indoor unit is actually drawing.
Auxiliary heat vs emergency heat is the comparison that matters on the display. Auxiliary heat works with the heat pump. It may come on during a defrost cycle, or when the house is far from the set point. You usually do not press anything. Emergency heat replaces the heat pump for that call. If you leave it on, the outdoor unit does not get a chance to do its efficient job, even on a mild La Jolla afternoon.
Normal heat-pump heating should be the default in San Diego County almost every day the system is in Heat. The emergency-heat thermostat setting is a bypass, not a second heating season. If you are using it because the house never quite reaches the set point, the next step is a licensed look at airflow, charge, outdoor-unit condition, and the thermostat and controls setup, not a permanent stay on Em Heat.
Do not treat the mode as a way to hurry recovery after you set the thermostat up several degrees. That is one of the most common mistakes on these controls. Recovery is a heat-pump and staging question. Forcing electric backup all afternoon does not fix a unit that is short of refrigerant, iced in a way it cannot clear, or wired to the wrong outdoor sensor.
Why many San Diego homes rarely need it
San Diego County is not one climate. Pacific Beach, Point Loma, and Carlsbad nights stay mild most of the year. Inland valleys in Escondido, Santee, and El Cajon drop lower after sundown. The backcountry around Julian, Descanso, and Palomar actually freezes. Even then, a working heat pump is built to heat in the weather we actually get here. A cold snap is not, by itself, a reason to switch to emergency heat.
True ice storms are rare in this county. A light frost on an Alpine roof, or steam coming off a condenser on a Mission Valley morning, is not the same thing as a failed outdoor unit. Steam and a thin coat of frost can be ordinary defrost. A unit that is locked in ice, silent, and blowing unconditioned air is a different problem. If you cannot tell the two apart from the driveway, do not guess with the thermostat. Have a licensed pro look at the outdoor coil and the control board.
Coastal houses almost never need this mode for weather. If a Point Loma heat pump is blowing cool air in January, the cause is more often a control, a sensor, a dirty filter, or a unit that has stopped heating, not outdoor air that is “too cold for a heat pump.” Inland and mountain homes see more hours where backup heat may assist on its own. That automatic assist is auxiliary heat, when the system is set up for it. You still should not park the thermostat on Emergency through a whole Ramona cold week.
The setting also does not replace a plan for a real equipment failure. If the outdoor unit is down, emergency heat can keep rooms livable while you arrange a licensed visit. It does not repair the heat pump. Leaving it on for days can hide the original fault. The house feels warm, the condenser never runs, and a problem that started as a sensor or a fan motor sits there until someone notices the electric bill or the quiet pad.
Use regular Heat through ordinary San Diego winter weather. Use emergency heat when the heat pump is out of the fight, not because a forecast looks chilly.
Signs the setting was left on by mistake
Emergency heat is easy to leave on after a guest, a night of troubleshooting, or a thermostat that was bumped on the wall. The house may still feel fine. That is what makes the mistake expensive and easy to miss.
Watch the display. Many stats show EM, AUX, or Emergency as a small flag. On some models the word stays on the home screen. On others you have to open the mode menu. If Heat is selected and a second heat flag never clears, even on a 65-degree afternoon in North Park, check that you are not sitting in emergency heat.
Listen for the outdoor unit. In regular heat, the condenser should run on a heating call once the system is past any short lockout the manufacturer programmed. If indoor air is warm, the air handler is loud, and the pad is silent call after call, the thermostat may be bypassing the outdoor unit. Confirm the mode before you assume the compressor is dead.
Feel the supply air and look at the timeline. Electric backup heat often feels hotter at the register than a heat pump’s steady, milder supply air. A sudden jump to very hot air, plus a quiet condenser, is a clue. So is a bill that moved hard after a week when you barely used the system. Heat Pro SD cannot quote what that bump “should” be. Compare the days the mode was on with your SDG&E usage and the indoor set point.
Guests and lockboxes create another local pattern. Vacation rentals in Ocean Beach and condos in downtown San Diego often have a wall stat that looks like a hotel control. Someone taps the first heat-looking option and lands on Em Heat. If the house was comfortable when you left and the outdoor unit has not run since, start with the mode screen, not a parts order.
Turn the thermostat back to regular Heat once you have confirmed that is what you want. Then watch one heating call. If the outdoor unit still never starts, or the air goes cool, you have a heat-pump problem, not a leftover setting. That is the moment to stop toggling modes and get a licensed independent HVAC contractor on site.
How it differs from a dual-fuel furnace backup
Electric emergency heat and a dual-fuel furnace are both backups. They are not the same machine and they are not the same thermostat logic.
On an all-electric heat pump, backup heat is usually electric resistance in the air handler or packaged unit. Emergency heat tells that electric backup to run alone. Dual-fuel, or hybrid, pairs a heat pump with a gas furnace. When the control decides the heat pump should step aside, the furnace fires. That changeover is a control setting, not the Em Heat button on a strip-heat system. If you are choosing equipment, start with hybrid dual-fuel systems and the heat pump vs gas furnace comparison, not with a thermostat label.
A dual-fuel thermostat may still show auxiliary or emergency language. The words can mean “run the furnace” on that job, or they can still mean electric strips if the indoor unit has both. You cannot read the menu in a vacuum. The matched pro has to know whether your backup is gas, electric, or a mix, and which terminals the stat is actually calling.
That difference matters in San Diego because plenty of East County and older inland houses still have a furnace in the closet and a heat pump or AC on the pad. Coastal replacements more often go all-electric. The right backup for a Julian freeze is a different conversation from a Mission Hills bungalow that rarely sees frost. Do not copy a neighbor’s thermostat screenshot and assume your backup fuel matches.
If your system is dual-fuel, do not use emergency heat as a shortcut around a changeover setting you do not understand. You can lock the furnace on, lock the heat pump out, or fight the outdoor sensor. Those are installer-level choices. They belong in the equipment manual and in a visit from a licensed contractor, not in a guess on a Sunday night.
Keep this page in its lane. Emergency heat here means the electric backup mode on a heat-pump thermostat. Furnace backup is a separate control story.
What to confirm before changing a control
Photograph the home screen, the mode list, and any installer or equipment menu before you change a thing. Note whether the system is in Heat, Auto, EM Heat, or a hold. If the stat is a late-model connected model, check the app too. The wall display and the phone do not always show the same mode.
Read the words on your thermostat, not a generic chart. Honeywell, ecobee, Google, and manufacturer stats all group heat-pump modes differently. The manual that came with the control, or the indoor unit’s installation literature, is the authority for what Emergency does on that job. If you do not have the paper, the brand’s current support page for your model is the next stop. Heat Pro SD cannot confirm a lockout temperature, strip-heat size, or staging rule for equipment we have not seen. Those figures are not on our verified claims list, and guessing them would be a problem for your system.
Do not rewrite installer settings to “fix” emergency heat. Staging, reversing-valve orientation, outdoor-sensor type, and dual-fuel changeover are how the heat pump and the backup stay in the right order. A wrong change can call heat while the outdoor unit is in cooling orientation, or keep strips on in weather that never needed them. If the menu asks for a configuration code, stop and get a licensed pro.
Check the obvious living-room items only. Confirm the set point is above room temperature, the schedule is not holding a low setback, and the filter is not choked. Look at the outdoor unit for debris, a tipped disconnect, or a dry, silent fan on a call for heat. If you smell gas on a dual-fuel job, leave the equipment alone and follow the utility’s instructions. For electrical or refrigerant work, California treats HVAC as licensed contractor territory. Confirm the person you hire on the CSLB license lookup.
When the setting still does not match what the house is doing, you need a licensed independent HVAC contractor, not another pass through the mode wheel. Heat Pro SD matches San Diego County homeowners with those pros and does not perform the work.
When to call us
Call when the outdoor unit will not heat, when emergency heat is the only mode that warms the house, or when you cannot tell Aux from Em Heat on your control. A licensed Heat Pump Installation contractor should read the thermostat, the indoor backup heat, and the outdoor unit together. Call us at (858) 400-4374 and we’ll connect you with a licensed local HVAC contractor.