Heat Pump Emergency Heat: What It Does and When to Use It

Short answer: Emergency Heat (often labeled EM Heat or E-Heat) turns off the outdoor heat pump and heats the house with backup heat only, usually electric heat strips in the indoor unit. Use it when the outdoor unit has failed or is badly iced and you're waiting for a repair. Don't leave it on as your everyday setting. Backup electric heat generally costs more to run, and your heat pump can usually handle Las Vegas winters on its own.

Safety first: if you smell gas (a rotten-egg smell), leave the house now and call 911 or Southwest Gas from outside. If a carbon monoxide alarm sounds, get everyone out and call 911 from outside. A dusty or oily smell the first time the heat runs each season is normal and can linger for a couple of days.

What "Emergency Heat" actually means

A heat pump moves heat from the outdoor air into your home. Most heat pump systems also have a second source of heat, called backup or supplemental heat. In most Las Vegas homes with heat pumps, that's a bank of electric heat strips in the indoor air handler. Some homes pair a heat pump with a gas furnace instead, which is called a dual-fuel system.

The Emergency Heat setting on the thermostat tells the system to stop using the heat pump entirely and run only on that backup heat. The outdoor unit stays off.

Emergency heat vs. auxiliary heat

These two terms confuse a lot of people, because they often use the same heat strips.

• Auxiliary heat (AUX) comes on automatically. The thermostat adds backup heat when the heat pump needs help, such as when you turn the setting up several degrees at once, or during a defrost cycle. The heat pump keeps running too. Seeing "AUX" on the screen now and then is normal.
• Emergency heat (EM) is something you choose. It switches the heat pump off and leaves only backup heat running until you change it back.

If you see AUX on the screen constantly, even on mild days, that can be a sign the heat pump isn't doing its share, and it's worth a service call. Our heat pump not heating guide covers that.

When to use Emergency Heat

Switch to Emergency Heat when:

• The outdoor unit isn't running and the house is getting cold, and you're waiting for a technician.
• The outdoor coil is covered in thick ice that isn't clearing after defrost cycles.
• The outdoor unit is making a grinding, banging or scraping noise, or you've seen smoke or smelled burning from it. Switching to Emergency Heat stops it from running while you wait for help.
• The outdoor unit is damaged, for example by a fallen object or a broken fan blade.

In each case, call to schedule a repair. Emergency Heat is meant to keep the house comfortable until then.

When not to use it

• As an everyday setting. Electric resistance heat strips generally use more electricity to make the same amount of heat than a working heat pump does. Leaving the system on Emergency Heat can raise your power bill noticeably.
• Because you saw steam. Steam from the outdoor unit on a cold morning is usually a normal defrost cycle.
• Because the air feels cooler than a gas furnace. Heat pumps deliver warm air at a lower temperature than a gas furnace, and they run longer cycles. That's normal. Our heat pump vs. furnace guide explains the difference.
• On cold nights, just in case. NOAA's 1991–2020 normals put the average January low in Las Vegas at 40.5°F and the average January high at 58.5°F. Heat pumps are designed to keep heating in conditions like these, with auxiliary heat filling in on its own when needed.

How to switch it on and off

Most thermostats show Emergency Heat as a mode alongside Heat, Cool, Auto and Off. On some it's a separate switch or a menu item. Check your thermostat's manual if you can't find it. If the screen is blank or the buttons don't respond, see our thermostat guide.

When the repair is done, switch back to Heat. A common surprise is a high electric bill weeks after a repair because the thermostat was left on Emergency Heat.

If Emergency Heat doesn't warm the house

If you switch to Emergency Heat and still get cool or room-temperature air, the problem may be in the indoor unit: the heat strips, their breakers, a sequencer or relay, or the blower. Check that the air handler's breakers haven't tripped. Heat strips often have their own breaker, separate from the outdoor unit's. If a breaker trips again after one reset, leave it off. Also check the filter, since low airflow can trip the strips' safety limits. See how to find your air filter size.

What not to do

• Don't leave Emergency Heat on after the outdoor unit is repaired.
• Don't keep resetting a breaker that trips again.
• Don't open the air handler to look at the heat strips. They carry line voltage.
• Don't chip ice off the outdoor coil.

When to call

If you've had to switch to Emergency Heat, the heat pump needs a look. Call if the outdoor unit won't run, stays iced, makes grinding noises, or if AUX shows almost all the time. See our Las Vegas furnace and heating repair service or our heat pump service.

FAQ

What does Emergency Heat do on a heat pump?

It turns off the outdoor heat pump and heats the house with backup heat only, usually electric heat strips in the indoor unit. It's meant for when the heat pump itself has a problem.

Is it bad to run a heat pump on Emergency Heat?

It won't hurt the system, but electric heat strips generally cost more to run than a working heat pump. Use it until a repair is done, then switch back to Heat.

What is the difference between AUX heat and Emergency Heat?

AUX heat comes on automatically to help the heat pump, which keeps running. Emergency Heat is a setting you choose that turns the heat pump off and runs backup heat only.

Should I use Emergency Heat on cold nights in Las Vegas?

Usually not. Heat pumps are designed to heat in typical Las Vegas winter weather, and auxiliary heat comes on by itself when it's needed. Use Emergency Heat when the outdoor unit has a problem.

Why is my thermostat showing AUX heat all the time?

Occasional AUX heat is normal. If it shows nearly all the time, even on mild days, the heat pump may not be heating properly and should be checked.

What hours can I reach Colton?

Colton Air Conditioning is open Monday to Friday, 8am to 5pm. You can call or book online during those hours.

Colton Air Conditioning

Colton Air Conditioning, 6545 S. Fort Apache Rd Ste 135 #467, Las Vegas, NV 89148. Nevada contractor license 0092120. Hours: Monday to Friday, 8am to 5pm. Call (702) 738-6976 or book online during those hours.

Want routine maintenance on a schedule? See our Comfort Club maintenance plans: Gold, Platinum and Diamond tiers are all listed there.