What Does 2nd Stage Heat Mean on a Thermostat?

Reviewed by Richard Morales, Co-Owner & FL Class B Air Conditioning Contractor (FL license CAC1819196)Updated Oct 16, 2026

Why Does Your System Have Two Stages?

One stage of heat handles most days. A second stage exists for the times one stage is not enough: a cold snap, a big temperature setback overnight, or a thermostat bump of several degrees at once. Running a lower stage most of the time is quieter and more efficient. The second stage is the reserve power that closes the gap when the first stage falls behind.

What 2nd Stage Means on a Heat Pump (Most Tampa Bay Homes)

Most homes in Tampa Bay heat with a heat pump paired with electric heat strips inside the attic air handler. That is the most common setup here, and it is the most common reason you see a 2nd stage indicator on a thermostat.

• 1st stage: The heat pump compressor runs. It pulls heat from outdoor air and moves it inside. This is the efficient stage.
• 2nd stage: The electric heat strips energize alongside the heat pump. Your thermostat may show AUX or AUX HEAT instead of a stage number. The strips add heat quickly but use more electricity.

The thermostat calls for 2nd stage automatically when the indoor temperature is still falling after the heat pump has been running for several minutes, or when you raise the setpoint by a large amount at once. That is normal behavior.

On a true two-stage heat pump compressor, 2nd stage means the compressor itself shifts to its higher capacity. The heat strips may still act as a third layer if needed.

AUX Heat vs. Emergency Heat: What Is the Difference?

These two terms confuse a lot of homeowners.

AUX heat is automatic and normal. Emergency heat is a manual override for when the heat pump itself has failed. Running emergency heat on a working heat pump wastes electricity and is not recommended. See our page on what to do when the emergency heat light is on for more detail.

What 2nd Stage Means on a Two-Stage Gas Furnace

Some Tampa Bay homes have a gas furnace paired with an AC system. A two-stage furnace has a low-fire and a high-fire burner setting. First stage is the low-fire setting for mild heating demand. Second stage is the high-fire setting for colder days or a large temperature gap. Seeing 2nd stage on a mild day with a gas furnace can mean the furnace is not reaching setpoint on low fire, which is worth checking.

When Is 2nd Stage Heat Normal?

• On a cold morning after overnight temperatures dropped into the 40s or below.
• Right after you raise the thermostat several degrees at once.
• During a setback recovery, when the system is catching up from a lower overnight setpoint.
• For short bursts of 10 to 20 minutes until the home reaches setpoint.

When Should 2nd Stage Heat Worry You?

2nd stage running constantly on a mild Tampa Bay day, say 55 to 65 degrees outside, usually means the heat pump is not doing its job and the strips are carrying the full load. Common causes include low refrigerant, a dirty filter or coil blocking airflow, a failed defrost board leaving the outdoor coil iced over, or a refrigerant metering device problem. Your power bill will climb fast when the strips run all day.

If your heat strips are not working at all, the opposite problem occurs: the heat pump alone cannot keep up and the home stays cold.

Safe Homeowner Checks Before You Call

How Home Therapist Can Help

Home Therapist Cooling, Heating and Plumbing serves Tampa Bay 24/7. Every visit includes a FREE estimate and FREE diagnosis, with no service call fee, no trip fee and no after-hours charge. Our licensed technicians can check your heat pump, test the heat strips, inspect the defrost board and refrigerant charge, and tell you exactly what is going on. Call or text us at (813) 343-2212 any time. You can also learn more about our heat pump repair services or browse our full heating services page.

Related: Thermostat Fan Auto vs On: Best Florida Setting

Frequently Asked Questions

• Is a two-stage heat pump worth it?

  Often yes in Tampa, where long, humid summers keep the system running. A two-stage unit runs on low most of the time, which gives steadier temperatures, better humidity removal and quieter operation than single-stage. The tradeoff is a higher upfront cost. We give a FREE estimate to compare options for your home.

• What does 2 stage heat pump mean?

  It means the compressor has two output levels: a low stage for most of the day and a high stage for extreme heat or cold. Running longer on low pulls more moisture from the air. Not to be confused with 2nd stage (auxiliary) heat, which is the backup electric heat strips.

• What are the common problems with a 2-stage air conditioner?

  Common problems include failed capacitors or contactors, faulty stage control boards or thermostat wiring, and clogged condensate drains from the long low-stage runtimes. Dirty coils and low refrigerant also hurt performance. Our FREE diagnosis pinpoints the cause, and you approve a written quote before any repair begins.

Is it bad if my thermostat shows AUX heat?

Not always. AUX heat is the same as 2nd stage on a heat pump system. Short bursts during cold mornings or after a big setpoint change are normal. The concern is when AUX runs for hours on a mild day, which usually points to a heat pump problem that a technician should diagnose.

Does 2nd stage heat cost more to run?

Yes. Electric heat strips use significantly more electricity than the heat pump compressor alone. The heat pump moves heat efficiently; the strips generate it directly. Frequent or constant 2nd stage use on mild days will raise your power bill noticeably.

Can I stop 2nd stage heat from turning on?

You can reduce how often it kicks in by avoiding large sudden setpoint changes and keeping your filter clean. But you should not disable it entirely. The strips are a safety net for cold snaps and heat pump failures. Disabling them leaves you without backup heat when you need it most.

What temperature outside causes a heat pump to need 2nd stage?

It depends on the system size and home insulation, but most heat pumps in Tampa Bay start leaning on the strips when outdoor temperatures drop below 40 degrees. A well-matched, properly charged heat pump may hold first stage down to the mid-30s before needing backup heat.

My heat pump runs but the house stays cold. Is that a 2nd stage problem?

It could be. If the heat pump is running but not heating well, and the strips are not energizing to help, you may have a failed heat strip, a tripped breaker on the strip circuit, or a heat pump refrigerant issue. A free diagnosis from our team will pinpoint the cause quickly.

How is 2nd stage different from emergency heat on my thermostat?

2nd stage or AUX heat runs the heat pump and the strips together automatically. Emergency heat shuts the heat pump off and runs the strips alone. Emergency heat is a manual override for a broken heat pump, not a normal heating mode. Using it on a working heat pump wastes electricity.