What Does EM Heat Mean on a Heat Pump? | Fort Collins

Fort Collins sits above 5,000 feet, and that elevation thins the air your heat pump depends on to pull warmth from outside.

When overnight temperatures drop into single digits, as they do most winters along the Front Range, homeowners glance at their thermostat and see an unfamiliar "EM HEAT" indicator lit up.

If you are asking what EM heat means, the short answer is that it is your heat pump's manual backup heat switch, and in most cases, you should not need it.

The confusion is understandable. A heat pump that is working correctly already uses backup heat automatically during the coldest stretches.

EM heat is different. It is a manual override, and turning it on when you don't need it can mean a much higher electric bill with no extra comfort to show for it.

EM Heat Decoded for Fort Collins Winters

EM stands for emergency. The emergency heat setting shuts off the heat pump's outdoor unit and forces the system to run only on electric resistance backup heat, bypassing the compressor and refrigerant cycle entirely.

That matters because it changes how your system behaves in a specific way:

• The outdoor unit stops running, even if it can produce heat.
• Your home heats entirely from indoor electric resistance coils.
• Energy costs typically rise, since resistance heat is less efficient than compressor-driven heat.
• The setting stays on until you manually switch it off.

Manufacturers built this switch for one purpose: keeping a house warm when the heat pump itself has failed, not for everyday cold snaps.

Why Fort Collins Elevation Makes This Switch Matter More

Thinner air at 5,003 feet means a standard heat pump has to work harder to extract the same amount of heat it would pull at sea level.

Combine that with Front Range weather swings of 30 to 40 degrees in a single day, and Fort Collins homeowners see heat pump stress signals more often than homeowners in milder climates.

A correctly specified cold-climate heat pump handles this without issue. For a full breakdown of how these systems are engineered for Northern Colorado's elevation and temperature swings, see McCormick's Definitive Guide to Cold Climate Heat Pumps in Fort Collins.

The homes most likely to see EM heat confusion in Fort Collins share a few traits:

• Older ductwork sized for a furnace, not a heat pump
• A heat pump that was never matched to the home's actual heating load
• A changeover setpoint left at the factory default instead of tuned to the house

Ready to find out if your heat pump is actually equipped for Fort Collins winters? Call McCormick Heating & Cooling, and we will test it before the next cold snap arrives.

EM Heat vs Aux Heat: What's Actually Different

This is where most of the confusion starts, because both settings turn on electric backup heat. The difference is who makes the decision.

Aux heat on thermostat mode is automatic. The thermostat switches on supplemental heat on its own when the heat pump cannot keep up with the demand, then switches back once the compressor catches up.

Heat pump aux heat is a normal, expected part of operation during cold weather and is not a sign of a problem by itself.

EM heat is manual. You, not the thermostat, decide to disable the heat pump entirely.

Aux Heat

EM Heat

Triggered by

Thermostat automatically

Homeowner manually

Heat pump compressor

Still running

Shut off completely

Normal frequency

Common on cold days

Rare, for failures only

If your thermostat shows "AUX" lit up on a 20°F morning, that is expected behavior. If "EM HEAT" is lit and you did not turn it on yourself, something triggered a lockout, and that is worth a call.

Why Your Heat Pump Blows Cold Air (And When It's Not an Emergency)

A heat pump periodically runs a defrost cycle to clear frost buildup from the outdoor coil, since frost blocks the coil from absorbing outdoor heat.

During this cycle, which typically lasts 5 to 15 minutes, the indoor fan can blow noticeably cooler air for 60 to 90 seconds. According to the U.S. Department of Energy's guide to heat pump systems, this is a perfectly normal, built-in function to prevent ice from crippling the unit, and it is not a reason to touch the EM heat switch.

Heat pump blowing cold air in winter becomes a real concern only when it happens outside a defrost cycle or lasts well beyond it. Signs worth a diagnostic call include:

• Air that stays cold for several minutes, not seconds
• Ice on the outdoor unit that does not clear after a defrost cycle
• Auxiliary heat running constantly on afternoons above freezing
• A squealing or grinding noise at startup

Even heat pumps built in 2026 with smarter defrost sensors still include a manual EM heat switch, because every heat pump, regardless of age, can experience a refrigerant leak, a failed sensor, or a stuck defrost cycle.

When Flipping to EM Heat Is the Right Call in Fort Collins

EM heat gets its name when the heat pump can't run safely or at all. Reasonable reasons to use it include:

• The outdoor unit is iced over and will not defrost
• You hear grinding, rattling, or an electrical burning smell from the outdoor unit
• A technician has advised you to use it while awaiting a repair part
• The compressor has failed, and a repair visit is already scheduled

Outside of those situations, leaving EM heat on is simply paying more to heat your home less efficiently.

McCormick's technicians test refrigerant charge, defrost operation, and changeover setpoint on every heat pump installation and repair visit, so you get an answer instead of a guess. You can see current homeowner reviews and reach the team directly through McCormick's Google Business Profile.

Key Takeaways

• EM heat is a manual, emergency-only override that shuts off your heat pump's compressor entirely
• Aux heat is automatic and normal during cold Fort Collins mornings, and is not the same thing as EM heat
• A brief burst of cool air during a defrost cycle is expected; cold air for several minutes is not
• If EM heat turned on by itself, or you are unsure why it is lit, call for a diagnostic before relying on it long term

Know the Switch Before Winter Tests It

Fort Collins winters are not gentle on heat pumps, and knowing the difference between aux heat, defrost mode, and true emergency heat keeps you from either panicking over normal operation or ignoring a real fault. The switch itself is simple.

What is happening behind it on a given night is the part worth getting checked by someone who tests it instead of assuming.

If your EM heat light is on and you did not put it there, do not wait for a colder night to find out why.

Contact McCormick Heating & Cooling to request service online, and a NATE-certified technician will tell you exactly what your system is doing and why.

Frequently Asked Questions

What is emergency heat on a heat pump?

In simple terms, emergency heat is a user-controlled mode that halts the heat pump's outdoor operation, shifting the entire heating burden to the secondary electric resistance system.

It exists for situations where the heat pump itself cannot run safely, such as a refrigerant leak, a failed outdoor fan, or ice that will not clear from the coil, and it typically increases electricity use compared to normal heat pump operation.

When should you use emergency heat on a heat pump?

You should use emergency heat on a heat pump only when the outdoor unit cannot run at all, such as during a confirmed mechanical failure, a persistent ice buildup that will not clear, or when a technician specifically instructs you to use it while a repair part is on order.

Using it for routine cold weather or during a normal defrost cycle is unnecessary and raises your heating costs without improving comfort.

What does aux heat mean on a thermostat?

Aux heat on a thermostat means the system has automatically activated supplemental electric heat because the heat pump's compressor alone cannot meet the home's current heating demand.

This happens on its own during cold weather and typically turns off once the compressor catches up, so it's normal heat pump operation, not a sign of malfunction.