Does Emergency Heat Kick On By Itself?
When temperatures plummet to freezing levels, homes need a reliable heating system to keep warm. Most HVAC (heating, ventilation, and air conditioning) systems have a primary heat source like a heat pump. But what happens if that main heating unit can't keep up on frigid days? This is where emergency heat comes in - it's a backup system designed to automatically kick in when needed.
Understanding how emergency heating works and when it activates can help homeowners optimize comfort and efficiency during cold weather.
What is Emergency Heat?
Emergency heat, also called auxiliary or backup heat, is a secondary heating system built into most heat pumps. It provides supplementary warmth when temperatures dip below 35degF and the heat pump struggles to maintain the indoor temperature setting. Emergency heat runs on electricity and uses heating elements like electric coils or strips. It directly warms the air without a heat exchange process.
Emergency heating is less efficient than the heat pump's normal operation. But it provides a failsafe heating source during defrost cycles or when heat pumps can't extract enough warmth from freezing outdoor air. Homeowners should avoid relying on emergency heat as the primary heating method. Prolonged use can strain the HVAC system and lead to high energy bills.
How Does Emergency Heat Work?
Emergency heat works independently from the heat pump and doesn't need the heat pump to trigger it. When indoor temperatures fall below the thermostat setting, emergency heat automatically switches on to warm up the home. It runs as needed until the indoor temperature reaches the desired level. The system then automatically turns off until activated again.
Most heat pumps have an indicator light labeled 'EM Heat' or something similar. This light switches on whenever the emergency heat engages. It alerts homeowners that the backup heating is running instead of the more energy-efficient heat pump. Emergency heat systems have their own wiring, switches, and controls separate from the heat pump's components.
Differences From Normal Heating
A key difference between emergency heat and normal heat pump heating is efficiency. Emergency heating uses simple electric resistance coils that directly convert electricity into heat. This takes more energy than a heat pump's heat exchange process. Running emergency heat for long periods can spike electricity bills.
Emergency heat also warms air differently than a heat pump. It relies solely on blowing hot air through ductwork. Heat pumps can also use hydronic heating systems to warm water and radiate heat. Hydronic heating can maintain more consistent temperatures.
When Does Emergency Heat Turn On?
Certain situations will automatically trigger emergency heat to turn on and prevent your home from becoming too cold. The main scenarios include:
- Cold outdoor temperatures below 30-40degF
- Heat pump unable to keep up during defrost cycles
- Thermostat set to emergency heat mode
- Malfunction with the heat pump
- Power failure affecting the heat pump
Once activated, the emergency heat will run until the indoor temperature reaches the level set on the thermostat. It does not need any manual switching on or interaction to start heating.
Outdoor Temperature Drops
A sudden cold snap that plunges temperatures into the 20s or 30s Fahrenheit can overpower a heat pump's capacity. Emergency heat automatically turns on as a failsafe once the outdoor temperature dips below the heat pump's effective operating range. The specific temperature threshold depends on the heat pump's specifications.
Defrost Cycle Activation
Heat pumps rely on extracting heat from outdoor air and can struggle when air temperatures fall below 45degF. Moisture and ice may build up on the outdoor heat exchanger coils. This frost accumulation inhibits the heat pump's efficiency. So heat pumps have a defrost cycle that temporarily switches into emergency heat mode to melt frost and restore full function.
Thermostat Settings
Many programmable thermostats have an emergency heat mode or setting. Selecting this triggers the backup heating whenever the temperature falls below the set point. Some thermostats require flipping a physical switch to emergency heat. Thermostats often have indicator lights showing when emergency heat engages. Homeowners can use the thermostat to manually override the heat pump and switch on emergency heat if desired.
How Does Emergency Heat Operate?
Emergency heating systems function independently and automatically switch on as needed to warm a home. Here are some key points about how backup emergency heat operates:
- Turns on without the heat pump triggering it
- Automatically maintains the temperature set on the thermostat
- Doesn't require flipping a switch or pressing a button
- Has its own wiring from the thermostat to control it
- Quickly warms air using electric heating elements
- Stops running once indoor temperature reaches the set point
This automated activation makes emergency heat convenient. Homeowners don't have to monitor weather forecasts and manually switch their system over. The emergency heat kicks in on its own to prevent the indoor temperature from dropping excessively. But homeowners should still avoid prolonged emergency heat use for optimal efficiency.
Wiring Differences
The thermostat wiring helps control the emergency heat independently. Most systems have R and W wires that connect to the thermostat's heat mode. Additional wires like E or AUX provide control signals specifically for emergency heat activation. So the heating can engage without any input from the heat pump's wiring.
Electric Heating Elements
Embedded electric coils or heating strips switch on when emergency heat activates. They rapidly convert electricity into heat. Tubular electric heaters may also warm and circulate air without relying on the heat pump's compressor and evaporation components. This provides a simple and reliable heat source.
Emergency Heat Temperature Settings
Getting emergency heat to turn on automatically requires proper thermostat programming. Here are guidelines for setting up emergency heat on programmable thermostats:
Enabling Emergency Heat Mode
Look for an operating mode or switch labeled 'Em Heat' or 'Auxiliary Heat' and activate it. This tells the thermostat to trigger emergency heat when needed. Refer to the thermostat's manual for model-specific instructions. Some only require adjusting software settings while others need a physical switch to be flipped.
Setting Temperature Triggers
Program the thermostat's heat setting to your desired home temperature, usually around 68-72degF. Set the heat pump and emergency heat modes to identical temperatures. Emergency heat will automatically activate whenever the indoor temperature drops below this set point.
Optimizing For Efficiency
Avoid setting emergency heat to turn on more than necessary. Keep the trigger temperature reasonable. Setting it too high can lead to overuse of the energy-intensive backup heating. Also inspect your home's insulation and air sealing to reduce heat loss.
Troubleshooting Emergency Heat Issues
If your emergency heat fails to activate when needed or runs excessively, some troubleshooting can get it working properly. Common problems include:
Emergency Heat Not Coming On
If your home feels cold but the emergency heat won't kick in, check your thermostat settings. Verify the system is not set to cool mode. Inspect the wiring to make sure emergency heat control wires are properly connected. Call an HVAC technician if settings appear correct but it still doesn't activate.
Emergency Heat Stays On
Constant running of emergency heat instead of your heat pump likely indicates an issue with the heat pump. Have an HVAC professional inspect the heat pump operation and refrigerant charge. Repair any detected problems so the system can resume using the more efficient heat pump for heating.
Excessive Emergency Heat Cycling
If you notice the backup heating turning on and off frequently, the cause may be a wide temperature swing in your home. Check for faults in the thermostat or HVAC system that prevent accurate temperature control. Adding insulation can also minimize emergency heat cycles.