EM Heat vs Heat: What’s the Difference and When Should You Use Each?

Overview

Heat is the normal, everyday setting for a heat pump, and EM Heat (Emergency Heat) is a backup mode you should switch to only when the heat pump cannot do its normal job — for example, during extremely cold weather or when the heat pump appears to have failed. The two settings are not interchangeable, and running EM Heat as your default can cost you more without any comfort benefit.

The key mechanical difference is simple: in regular Heat mode, your heat pump uses the outdoor unit to move heat into your home, while EM Heat bypasses the outdoor unit and relies on backup heat instead. The rest of this guide explains what each mode does and how to decide which one you need right now.

What Heat mode does

Heat mode is the setting your heat pump is designed to run in for normal heating. When your thermostat is set to Heat, the system uses the outdoor unit to pull heat from the outside air and move it indoors — the same basic process it uses for cooling, just running in the opposite direction, as Beacon’s heat pump guide explains.

For most of the heating season, this is the only setting you need. The heat pump handles the workload, the outdoor unit runs as expected, and you simply set the temperature you want. If your home is warming up normally, there is no reason to touch the EM Heat switch at all.

One thing that surprises beginners: heat pumps can behave differently from furnaces. The air from the vents may feel milder than furnace air, and the outdoor unit may cycle in ways that seem unusual if you are used to other equipment. Milder-feeling air on its own is not proof that something is broken. The practical rule is this — as long as the thermostat is set to Heat and the home is reaching the temperature you set, leave the system alone and let it do its normal work.

What EM Heat does

EM Heat stands for Emergency Heat, and it is a manually selected backup mode — not a stronger version of regular heating. According to Jon Wayne’s explainer on EM Heat, the setting is recommended only when necessary, such as during extremely cold weather or when the heat pump is not working properly.

When you switch to EM Heat, the system stops relying on the outdoor heat pump unit to gather heat. As Beacon describes it, EM Heat bypasses the outdoor unit and heats your home using the system’s backup heat source instead. In many heat pump setups, that backup source is a set of electric heating elements — often called heat strips — inside the indoor equipment, though the exact backup arrangement depends on how your system was installed. The important point is that EM Heat is a way to keep the house warm while the normal heat pump process is out of the picture.

Because EM Heat sidesteps the heat pump’s normal operation, it also sidesteps the efficiency that makes heat pumps attractive in the first place. That is why every source in this comparison treats it as a temporary measure. As Florida Breeze puts it, Heat and Emergency Heat are not interchangeable — each serves a specific purpose. Think of EM Heat as the spare tire of your heating system: essential when you need it, but not something you drive on indefinitely.

When to use Heat vs EM Heat

The short answer: stay on Heat unless the heat pump genuinely cannot keep up or appears to have a problem. Jon Wayne’s guidance is to use EM Heat only when necessary — extremely cold conditions or a heat pump that is not functioning are the two situations that justify it. Everything else is either normal operation or a question for a technician.

The matrix below maps the most common situations to the setting and action that fit them. It deliberately sticks to high-level scenarios; if your situation involves visible damage, electrical smells, or repeated breaker trips, skip the matrix and contact a professional.

Situation	Recommended setting	What else to do
Home is heating normally	Heat	Nothing — this is normal heat pump operation
Very cold snap and the heat pump can’t keep the home warm	EM Heat, temporarily	Return to Heat once conditions moderate; if this happens often, ask a technician about your system
Heat pump appears broken (outdoor unit not running, no heat at all)	EM Heat, temporarily	Schedule service; EM Heat is a stopgap, not a fix
EM Heat was switched on by accident and heating works fine	Heat	Switch back — leaving EM Heat on unnecessarily can raise energy use
Heating trouble that basic checks don’t resolve	Either, depending on comfort	Contact an HVAC technician for diagnosis

Two of these rows deserve extra emphasis. First, accidental EM Heat use is common — the labels sit next to each other on many thermostats, and a house that still feels warm gives no obvious signal that anything changed. If you discover EM Heat is on and you never had a heating problem, simply switch back to Heat. Second, climate matters: in regions with long stretches of severe cold, backup heat engaging is a more routine part of winter than it is in mild climates, so a single very cold night is not automatically a sign your heat pump has failed. When in doubt, treat EM Heat as a bridge to a solution, not the solution itself.

How long to leave EM Heat on

Leave EM Heat on only as long as the situation that justified it lasts — there is no universal hour or day limit, but the mode is meant to be temporary. Jon Wayne’s guidance frames EM Heat as a setting to use only when necessary, which implies switching back to Heat as soon as the necessity ends.

In practice, that means two exit points. If you switched to EM Heat because of an extreme cold spell, return to Heat once temperatures recover and the heat pump can carry the load again. If you switched because the heat pump seemed broken, keep EM Heat on until a technician repairs the system, then set the thermostat back to Heat and confirm the home warms normally. Leaving EM Heat running after the repair just wastes the fix you paid for.

Aux Heat vs EM Heat

Aux Heat and EM Heat are related but not the same thing, and the biggest practical difference is who turns them on. EM Heat is a mode you select manually at the thermostat. An AUX Heat indicator, by contrast, typically appears when the system calls on backup heat automatically to supplement the heat pump — for instance, when the heat pump alone is struggling to hit the set temperature. In that automatic case, the outdoor unit is generally still part of the picture, whereas EM Heat bypasses the outdoor unit entirely.

A useful mental shortcut: AUX appearing on its own usually means the system made a decision; EM Heat on the display usually means a person made a decision. Seeing AUX during very cold weather is not necessarily a fault — it can simply be the backup heat helping out.

That said, thermostat wording varies widely. Depending on your equipment and how it was configured, you might see EM HEAT, AUX HEAT, Emergency, or Backup Heat, and the exact behavior behind each label depends on your specific thermostat and system setup. If a label on your display doesn’t match what this article describes, check your thermostat’s manual or your system documentation before assuming something is wrong. The safe default remains the same: don’t manually select emergency or backup modes unless the heat pump can’t do its job.

Why EM Heat can affect your power bill

Running EM Heat unnecessarily can push your electric bill up, because backup heating is generally a less efficient way to warm your home than normal heat pump operation. The heat pump’s efficiency comes from moving heat with the outdoor unit; when EM Heat bypasses that process, the backup heat source has to generate warmth more directly, which typically demands more electricity for the same comfort.

None of the sources in this comparison publish a reliable dollar figure for that difference, and this article won’t invent one. A meaningful estimate depends on at least three inputs specific to your situation: your local electric rate per kilowatt-hour, the wattage of your system’s backup heating elements, and how many hours the backup heat actually runs. Your utility bill shows the first number; the second usually requires your system’s documentation or an installer; the third depends on weather and your thermostat settings.

The practical takeaway doesn’t require math, though. Every extra hour on EM Heat that you didn’t need is an hour of avoidable cost — and it can also mask a heat pump problem that will still be there when the bill arrives. Use EM Heat when the situation calls for it, and switch back promptly.

What to check before switching to EM Heat or calling for service

Before flipping to EM Heat or booking a service call, spend a few minutes ruling out simple explanations. Many “no heat” moments turn out to be a setting, a switch, or something visible from outside — and confirming the basics also gives a technician better information if you do end up calling. These are observation-level checks, not repairs; if anything requires opening equipment, stop and call a professional.

• Confirm the thermostat is set to Heat (not Cool, Off, or an accidentally selected EM Heat) and that the set temperature is above the current room temperature.
• Check whether the thermostat display is behaving normally — a blank or unresponsive display points to a power or thermostat issue rather than a heat pump failure.
• Look at your electrical panel for a tripped breaker serving the HVAC system.
• Check your air filter; a heavily clogged filter can restrict airflow and hurt heating performance.
• Look at the outdoor unit from a safe distance: is it running when the system calls for heat, and is it free of debris, snow, or heavy ice buildup?

If these checks reveal an obvious fix — a wrong setting, a dirty filter, a tripped breaker you can safely reset once — correct it and give the system time to respond on regular Heat. If the outdoor unit isn’t running, is encased in ice, or the home still won’t warm up, that’s the point where EM Heat as a temporary bridge plus a service call is the right combination. Don’t attempt to defrost, dismantle, or repair the outdoor unit yourself, and treat a breaker that trips repeatedly as a reason to call, not reset again.

If your home is still cold on EM Heat

If you’ve switched to EM Heat and the house still isn’t warming up, treat that as a sign the backup heat itself isn’t doing its job — and a strong signal to call for service. Florida Breeze’s comparison addresses this exact scenario, and the underlying logic is straightforward: EM Heat exists to keep you warm when the heat pump can’t, so a cold home on EM Heat means both your primary and backup heating paths have a problem.

The possible causes range from a tripped breaker on the backup heat circuit to a thermostat configuration issue, an airflow restriction, or a fault in the backup heating elements. Pinpointing which one applies usually requires equipment access and testing that isn’t safe or practical for a non-technical user, so this is not a situation to troubleshoot deeply on your own. Recheck the basics from the previous section — thermostat setting, breakers, filter — and if the home still stays cold, contact an HVAC technician and describe both symptoms: the original heat pump issue and the fact that EM Heat isn’t keeping up.

Which systems usually have an EM Heat setting

EM Heat is primarily a heat pump concept, and everything in this article is written for heat pump thermostats. The setting exists because a heat pump has a distinct backup heat source it can fall back on when the normal outdoor-unit process isn’t available — a design that other heating systems don’t necessarily share.

If your home has a conventional furnace with no heat pump, your thermostat typically won’t offer an EM Heat mode, because there is no separate backup path to switch to. Other configurations — dual-fuel systems that pair a heat pump with a furnace, geothermal heat pumps, and ductless mini-splits — handle backup heating in their own ways, and their controls and labels can differ from the standard air-source setup described here. The evidence behind this article doesn’t cover those variations in detail, so treat their behavior as system-specific rather than assuming this guide applies directly.

The practical close: if your thermostat shows an EM Heat option, you most likely have a heat pump, and the rules here apply — Heat for everyday use, EM Heat only when genuinely necessary, and a service call when neither keeps your home warm.