A cold front rolls into Georgia, temperatures drop into the low twenties, and you notice your heat pump is running constantly. You glance at your Honeywell thermostat and see a setting labeled "EM Heat". Should you turn it on to give the system a boost?
Absolutely not. Switching your thermostat to "EM Heat" (Emergency Heat) during cold weather is one of the most common—and most expensive—mistakes homeowners make. At HVAC Bee, we frequently get calls from homeowners wondering why their winter electricity bills have tripled, and the culprit is almost always this single switch.
What is EM Heat?
To understand EM Heat, you first have to understand how your Heat Pump works.
A heat pump doesn't actually create heat; it moves it. Even when it's cold outside, there is still heat energy in the air. The outdoor unit extracts this heat and pumps it inside your house. Because moving heat requires far less energy than creating it, heat pumps are incredibly energy efficient.
The Backup Plan: Auxiliary Heat
However, when the temperature drops below freezing, there isn't enough heat in the outside air for the heat pump to extract efficiently. When this happens, the system automatically turns on its "Auxiliary Heat" (Aux Heat).
Auxiliary heat consists of large electric resistance coils (heat strips) located inside your indoor air handler. They act just like the glowing red coils inside a toaster. The thermostat turns them on temporarily to assist the heat pump, and turns them back off once the house is warm.
What EM Heat Actually Does
When you manually flip your thermostat to EM Heat, you are commanding the system to completely shut down the efficient outdoor heat pump. You are locking it out.
Instead, the system relies 100% on those electric heat strips to heat your entire home. You have essentially turned your home's central heating system into a giant, incredibly inefficient space heater.
When Should I Use Emergency Heat?
The clue is in the name: it is strictly for emergencies. You should never turn it on simply because it is cold outside (your system will use Aux Heat automatically for that). You should only manually engage EM Heat if your primary outdoor heat pump is physically incapable of running.
The Outdoor Unit is Frozen Solid
If you look at your outdoor unit and it is encased in a thick block of solid ice, it cannot operate. Turn on EM Heat to keep your house warm while you wait for it to thaw (and call for an HVAC diagnostic).
Physical Damage to the Unit
If a falling tree branch crushes the outdoor fan, or if you notice the outdoor unit is making a violent screeching noise and refusing to spin, switch to EM Heat to prevent further damage to the compressor.
Blowing Cold Air
If your heat pump is running but blowing completely cold air out of the vents during a winter freeze, the compressor or reversing valve may have failed. EM Heat will bridge the gap until a technician arrives.
The Cost of Emergency Heat
Running your HVAC system entirely on electric heat strips is the most expensive way to heat a home. Because they draw massive amounts of electricity to create raw heat, running EM Heat continuously for just a few days can easily double or triple your monthly electric bill.
What is that burning smell? If you turn on EM Heat (or if your Aux Heat kicks on for the first time in winter), you will likely smell a faint burning odor. This is completely normal. Dust settles on the heat strips during the summer, and when they ignite, the dust burns off. The smell should dissipate within 15 to 30 minutes. If you smell melting plastic or smoke, turn the system off immediately at the breaker and do not attempt to restart it.
Emergency Heat is a fantastic safety net. It ensures that if your primary system dies in the dead of winter, your family will not freeze while waiting for an HVAC Bee technician. However, treat it like a spare tire on your car: use it only when you absolutely have to, and get the main issue fixed as quickly as possible.
