A heat pump blowing air that feels cool on your hand is usually working exactly as designed, and the real problem is somewhere else. Heat pumps move heat rather than create it, so the air they deliver is warmer than the room but often cooler than your skin, which your hand reads as cool even while the house steadily warms. Longer, gentler cycles are normal here, not a fault. What should concern you is auxiliary heat running often, because those electric resistance strips are the expensive way to heat a house, and the Department of Energy puts air-source heat pumps at up to 75 percent less electricity use for heating than electric resistance. In Phoenix, where December and January lows average in the mid-40s and a freeze happens about once a year, your heat pump should carry nearly the entire winter on its own. If the strips cycle on regularly, the fix is usually one of three things: shallower overnight setbacks, a thermostat configured for this climate rather than a cold one, or a diagnostic on a system that is quietly losing capacity.
Adams Refrigeration has served the Valley since 1947 and is a member of the Arizona Heat Pump Council as well as a Carrier Factory Authorized Dealer, licensed under Arizona ROC 245268. Heating gets a fraction of the attention cooling does in Phoenix, which is exactly why homeowners here overpay for it without noticing. Here is how the three kinds of heat work, what should and should not be happening in a Phoenix winter, and when a service call is warranted.
Phoenix Winters Are Mild, Which Changes Everything
| Month | Average high | Average low |
|---|---|---|
| December | 66 degrees | 45 degrees |
| January | 68 degrees | 46 degrees |
| February | 71 degrees | 49 degrees |
Those are 30-year normals, and the Phoenix monthly temperature record shows freezing weather is roughly an annual event rather than a season.
This matters more than it sounds. Heat pumps lose capacity as outdoor temperatures fall, and the temperature where a heat pump’s output exactly matches the house’s heat loss is called the balance point. Below it, the system needs help. Above it, it does not.
Phoenix sits above a typical residential balance point for almost the whole winter. That is why heat pumps dominate here and why gas furnaces are far less common than in colder markets. Our comparison of heat pumps versus AC covers how the same equipment handles both seasons.
The practical takeaway: in this climate, strip heat should be a rare backup, not a regular participant.
The Three Kinds of Heat
Understanding which one is running is most of the battle.
Compressor Heat
The heat pump reversing its refrigerant cycle to pull heat from outdoor air and move it inside. This is the efficient mode and it should be doing nearly all the work in Phoenix.
Air from the registers feels mild rather than hot. Cycles run longer. Both are correct.
Auxiliary Heat
Electric resistance strips in the air handler, which turn electricity directly into heat at roughly one unit of heat per unit of electricity. The heat pump, by contrast, delivers several units of heat per unit of electricity, which is the entire efficiency argument.
Auxiliary heat is designed to supplement the compressor when the compressor alone cannot keep up. Common triggers:
Outdoor temperature falls below the configured aux trigger, often set near 40 degrees
The system enters a defrost cycle
You raise the thermostat more than about three or four degrees at once
That last trigger is the one that quietly costs Phoenix homeowners money, and it has nothing to do with the weather.
Emergency Heat
A thermostat setting, usually labeled EM HEAT, that shuts the compressor off entirely and heats the house on strips alone.
This exists for one situation: the heat pump has failed and you need heat until it is repaired. It is not a boost button, and it is not the setting to reach for on a chilly morning. Running a Phoenix winter on emergency heat produces a power bill people remember.
Tip: Look at your thermostat right now and find out whether it has an EM HEAT setting and whether it is engaged. People switch it on during a cold snap, forget it, and run resistance heat for weeks.
The Setback Trap
This is the single most common reason Phoenix heat pumps run strip heat, and it is entirely self-inflicted.
With a gas furnace, deep nighttime setbacks save money. You drop the temperature eight degrees overnight, the furnace blasts back up in the morning, and you come out ahead. That habit transfers badly to a heat pump.
A heat pump recovers slowly by design. When you ask for a large jump, the thermostat concludes the compressor cannot get there fast enough and brings the strips online to close the gap. You spend the morning heating your house the expensive way, and the savings from the setback are gone and then some.
What works better with a heat pump:
Keep setbacks small, within two or three degrees
Or hold a steady temperature through the night
Let a smart thermostat handle recovery gradually rather than demanding a jump
Avoid manually overriding by large amounts
A thermostat with adaptive or intelligent recovery ramps the temperature up slowly and well ahead of your schedule, which keeps the strips out of it. Our comparison of smart and programmable thermostats covers which features actually matter, and our notes on thermostat settings for Phoenix cover the cooling side of the same logic.
Tip: If your thermostat has an aux heat lockout or an adjustable aux trigger temperature, have it set appropriately for this climate. A thermostat installed with cold-climate defaults will bring on strips far earlier than a Phoenix house needs.
Defrost Is Rare Here, Which Is Useful to Know
In humid winter climates, outdoor coils ice up and the system periodically reverses to melt it. During defrost, the strips run to keep indoor air from turning cold, and you may see steam rising off the outdoor unit.
Frost formation needs both cold and moisture. Phoenix winters are dry, so defrost cycles are uncommon compared with most of the country. You may see one on a cool, damp morning after rain.
So if your outdoor unit is icing up repeatedly in Phoenix, that is worth a look rather than a shrug. Repeated icing in a dry climate points at low refrigerant, restricted airflow, or a defrost control problem. Our guide to low refrigerant symptoms applies to heating season too, since the same charge serves both modes.
When Something Is Actually Wrong
Normal Phoenix heat pump behavior:
Mild air from the registers
Long, steady run cycles
Occasional brief strip operation during a genuine cold snap
A quiet clunk when the reversing valve switches modes
Worth a service call:
| Symptom | Likely issue |
|---|---|
| Strips running constantly in mild weather | Thermostat config, low charge, or failing compressor |
| No heat at all, cool air only | Reversing valve or compressor fault |
| Outdoor unit icing repeatedly | Low refrigerant, airflow, or defrost control |
| Loud grinding or screeching | Mechanical fault, shut it down |
| Heat works, cooling does not, or vice versa | Reversing valve stuck |
| Breaker tripping in heating mode | Strip heat circuit problem |
That reversing valve pattern is distinctive to heat pumps. A system that cools fine but will not heat, or the reverse, has usually lost the ability to switch modes rather than lost its ability to move heat. Our guide to unusual system noises covers what different sounds indicate, and our notes on professional AC repair cover what is worth a diagnostic.
Heating Season Is the Time for Maintenance
Phoenix has this backwards, and it is costing people equipment life.
Everyone services their system in spring, bracing for summer. Almost nobody services it in fall. But a heat pump here runs eight or nine months of cooling and then switches to a heating mode that has sat unused since March. The reversing valve, the defrost board, and the strip heat sequence have all been idle.
A fall check catches the things that only show up in heating mode, and it does it in October rather than on the first cold morning when every contractor in the Valley is booked. Our overview of regular maintenance covers the schedule, and our Phoenix winterizing guide covers the rest of the house.
Tip: Run your heat for twenty minutes on a mild October afternoon, before you actually need it. If something is wrong with the heating side, you want to find out on a 70-degree day with the schedule open, not at 6 a.m. in January.
If You Are Replacing a System
A few heating-specific points that get lost in cooling-focused conversations.
Heat pumps carry an HSPF2 heating efficiency rating alongside SEER2 for cooling, and the national minimum for split system heat pumps is 14.3 SEER2 and 7.5 HSPF2. In a climate where heating load is light, the cooling ratings deserve most of your attention, but the heating number is not meaningless.
Variable capacity equipment suits Phoenix heating well. It can run at low output for long periods, which is exactly what a mild winter calls for and exactly what keeps strips offline.
Sizing is still driven by the cooling load here, which is correct, but make sure whoever quotes you configures the aux heat staging and thermostat for this climate rather than leaving factory defaults. Our AC installation guide covers what a proper install includes, and anyone weighing replacement should also understand the refrigerant transition now affecting new equipment.
Frequently Asked Questions
Why does my heat pump blow cool air in heating mode?
Because it moves heat rather than generating it, a heat pump delivers air that is warmer than the room but often cooler than your skin. Air around 90 degrees feels cool to the touch while still heating the house effectively.
What is auxiliary heat on a heat pump?
Electric resistance heat strips that supplement the compressor when it cannot meet demand alone. They heat effectively but use far more electricity, since the Department of Energy puts heat pumps at up to 75 percent less electricity use than resistance heating.
Should I use emergency heat in Phoenix?
Only if the heat pump itself has failed. Emergency heat shuts off the compressor and runs on strips alone, which is the most expensive way to heat a home. It is a backup, not a boost.
Why is my heat pump running auxiliary heat in mild weather?
Most often a thermostat set back too deeply overnight, or a thermostat configured with cold-climate defaults. It can also indicate low refrigerant or a failing compressor, so it is worth diagnosing if settings are not the cause.
Should I set my thermostat back at night with a heat pump?
Keep setbacks small, within two or three degrees, or hold steady. Large setbacks trigger strip heat during recovery, which usually costs more than the setback saved.
When should I service the heating side of my system?
October, before the first cold morning. The heating mode sits unused from spring through fall, and a fall check catches reversing valve, defrost, and strip heat faults while contractor schedules are still open.
Heating Service in the Valley
Adams Refrigeration has served Phoenix since 1947, covering Glendale, Tolleson, Litchfield Park, Goodyear, Avondale, Buckeye, Peoria, Waddell, and Sun City. Our HVAC Experts in Phoenix handle heat pump repair and installation, furnaces and gas heating, AC installation and repair, ductless mini-splits, duct replacement, and indoor air quality.
We are a Carrier Factory Authorized Dealer, a Carrier President’s Award recipient, an Arizona Public Service Qualified Contractor, and a member of the Arizona Heat Pump Council, licensed under Arizona ROC 245268. Call (602) 269-6447 any hour and we will find out why your strips are running.