Emergency Heat Vs Auxiliary Heat

The short answer first

Aux heat and emergency heat both use the same backup strips. The difference is the heat pump itself.

With aux heat, the heat pump runs and the backup helps. With emergency heat, the heat pump is off and the backup does all the work.

For everyday use, leave the thermostat on plain HEAT. Save emergency heat for when the heat pump is broken or iced over and you need heat right now.

Get this right and you keep your bill down. Mix them up, and you can pay far more than you need to all winter long.

• Both settings use the same costly backup strips.
• Aux heat: heat pump plus backup together.
• Emergency heat: backup only, heat pump off.
• Use plain HEAT day to day.

What auxiliary heat does

Auxiliary heat is automatic. You do not turn it on.

The thermostat brings it in when the heat pump alone cannot keep up.

On a cold Frederick day, the heat pump may fall behind. The backup strips switch on to help, and the thermostat shows aux heat.

The two run together until the house catches up.

Aux heat also shows up when you raise the setpoint several degrees at once. The system calls for backup to warm the house quickly.

So aux heat on a cold morning, or after a big setpoint jump, is the system working as designed. It is the steady, all-day aux heat in mild weather that points to a problem.

You do not need to do anything when aux heat appears in the cold. The thermostat drops it on its own once the house catches up and the heat pump can carry the load again.

• Aux heat turns on by itself, not by your choice.
• It helps when the heat pump cannot keep up in cold.
• A big setpoint jump also calls for aux heat.
• All-day aux heat in mild weather is a warning sign.

What emergency heat does

Emergency heat is a setting you choose. When you select it, the heat pump shuts off completely and only the backup strips run.

It is meant for when the heat pump cannot run at all. Maybe the outdoor unit is iced solid, the fan failed, or a part broke.

Emergency heat keeps the house warm while you wait for repair.

It is not for everyday cold. The backup strips alone use a lot of power, so running emergency heat for days runs up a steep bill.

Think of it as a stopgap. Use it to stay warm until a tech fixes the heat pump, then switch back to plain HEAT.

Many newer thermostats turn on a small light or icon when emergency heat is active. That reminder helps, since it is easy to forget the setting and pay for it later.

• Emergency heat is a setting you turn on yourself.
• It shuts the heat pump off and runs only the backup.
• Use it when the heat pump cannot run at all.
• It is a stopgap, not an everyday setting.

When to use each setting

For nearly all winter days, leave the thermostat on plain HEAT. The system runs the heat pump first and pulls in aux heat only when it needs to.

That is the cheapest way to stay warm.

Do not switch to emergency heat just because it is cold. Plain HEAT already brings in backup when needed, and it does so more efficiently than emergency heat.

Switch to emergency heat only when the heat pump itself is down. If the outdoor unit is iced solid, silent, or clearly broken, emergency heat keeps heat coming while you wait.

Once a tech repairs the heat pump, switch back to plain HEAT. Leaving it on emergency heat by mistake is a common cause of a shockingly high bill.

• Use plain HEAT for nearly every winter day.
• Do not switch to emergency heat just because it is cold.
• Use emergency heat only when the heat pump is down.
• Switch back to plain HEAT after a repair.

What each setting costs

The heat pump is the cheapest way to heat. It moves heat instead of making it, so it stretches your power further.

The backup strips are the opposite. They make heat directly, which uses a lot of power.

That is true whether the strips run as aux heat or as emergency heat.

Aux heat costs more only while it runs, and on plain HEAT it runs just enough to fill the gap. Emergency heat costs the most, since the efficient heat pump is off the whole time.

So the cheapest setup is plain HEAT, letting the heat pump do most of the work. Emergency heat for days at a time is the most expensive way to heat your home.

• The heat pump is the cheapest heat source.
• Backup strips use a lot of power either way.
• Plain HEAT runs the backup only as needed.
• Emergency heat for days is the costliest setup.

Seeing aux heat does not mean it is broken

Many people panic the first time they see aux heat on the screen. In cold weather, it is usually normal.

A heat pump pulls heat from outside air. The colder it gets, the less heat there is to pull.

Below a certain outdoor temperature, the heat pump needs the backup to keep up.

So aux heat in single-digit cold is expected. It is the system doing exactly what it should to hold your setpoint.

The concern is aux heat that runs when it should not. Aux heat in mild weather, or aux heat that never shuts off, is the sign that something needs a look.

• Aux heat in cold weather is usually normal.
• The heat pump needs help below a certain temperature.
• Aux heat in single-digit cold is expected.
• Aux heat in mild weather is the real warning sign.

When the setting points to a repair

If aux heat runs all the time, even in mild weather, the heat pump is not doing its share. Then the backup carries the house and your bill climbs.

Start with the simple causes. A dirty filter, an iced outdoor unit, or a deep night setback can all push the system onto backup more than it should.

If those are clear and aux heat still runs nonstop, the cause is often low refrigerant or a worn part. Low charge means a leak.

A bad defrost board or reversing valve can also be the cause.

If you find the thermostat stuck on emergency heat and no one set it, that can point to a wiring or control fault. A tech can check the setup.

• Nonstop aux heat in mild weather points to a problem.
• Check the filter, outdoor unit, and setbacks first.
• Low charge or a worn part is a common deeper cause.
• A thermostat stuck on emergency heat can be a control fault.

Check the thermostat setup

A heat pump needs the right thermostat, set up the right way. The wrong setup makes aux heat and emergency heat behave oddly.

Some thermostats are not built for heat pump staging. Others are wired wrong, so the backup runs when it should not.

If the settings look right but the behavior is off, the setup may be the issue.

Check the basics yourself. Make sure the mode is plain HEAT, the schedule is not jumping the setpoint, and the battery is good if the screen is dim.

If aux heat still misbehaves after that, leave the deeper setup to a tech. Staging and low-voltage wiring are not homeowner jobs.

• A heat pump needs the right thermostat, set up right.
• Wrong staging or wiring makes backup run too much.
• Check the mode, schedule, and battery yourself.
• Leave staging and wiring to a tech.

When to stop and call right away

Most heat-setting questions are about comfort and cost, not danger. But a few are not.

Turn the system off and call right away for a burning smell, smoke, a breaker that keeps tripping, or water spreading toward walls or wiring.

If you smell gas or a CO alarm goes off, leave the house first. Call from outside.

Do not flip switches or light anything.

Backup heat strips draw a lot of power. If a breaker tied to the heat trips again and again, stop resetting it.

That is an electrical fault for a tech.

For a normal problem, the rule is simple. If you have to run emergency heat to stay warm, the heat pump needs repair.

Call so you can get back to normal heating.

• Leave the house for a gas smell or a CO alarm, then call.
• Turn it off for burning smells, smoke, or repeated breaker trips.
• Stop resetting a breaker that keeps tripping on the heat.
• If you need emergency heat to stay warm, call for repair.

What We Check During Repair

A technician connects the heat-setting problem to a real test, not a guess. Expect them to check the thermostat staging and wiring, then verify how the backup strips come in.

They should also measure the refrigerant charge and check the defrost cycle. These tests tell apart causes that look the same from your thermostat.

Wrong staging, low charge, and a worn part can all force the backup to run too much, but each needs a different fix. The test points to the right one.

Ask what they found and what the test showed before you approve any parts. If the visit jumps straight from a small repair to replacing the whole system, ask them to explain why.

• Expect a thermostat staging and wiring check.
• Expect a charge check and a defrost check.
• Ask what the tests showed before approving parts.
• Ask why, if they suggest full replacement over a repair.

What to do while you wait

If the heat pump still runs, leave the thermostat on plain HEAT. That lets the heat pump do the cheap work and pulls in backup only as needed.

If the heat pump is down and you need warmth, switch to emergency heat as a stopgap. Just remember it costs the most, so use it only until the repair is done.

Stay comfortable with simple steps. Close doors to rooms you are not using.

Open blinds on the sunny side during the day. Layer up to hold a lower setpoint.

Write down what you saw. Note which mode you used, how often aux heat showed up, the outdoor temperature, and any change in your bill.

A short list saves the tech from repeating your steps.

• Leave a working heat pump on plain HEAT.
• Use emergency heat as a stopgap only if the heat pump is down.
• Close unused rooms and dress warmer to hold a lower setpoint.
• Write down which mode you used and how aux heat behaved.