Use emergency heat on your thermostat during extreme cold when your heat pump struggles to maintain indoor temperature or during system malfunctions.
Emergency heat is a critical feature on heat pump thermostats, but many homeowners misuse it – leading to high energy bills and potential system damage. Understanding when and how to use emergency heat can save you money and keep your home comfortable during extreme cold.
What Is Emergency Heat?
Emergency heat (often labeled “Em Heat” on thermostats) is a backup heating system that activates when your primary heat pump can’t maintain comfortable temperatures. Unlike regular heating, emergency heat bypasses the heat pump entirely and uses alternative heating elements.
How Emergency Heat Works
When activated, emergency heat:
- Shuts off the outdoor heat pump unit completely
- Activates electric resistance coils (or gas/oil furnace if equipped)
- Provides direct heating without outdoor air exchange
When to Use Emergency Heat
Only use emergency heat in these specific situations:
1. Heat Pump Failure
If your heat pump stops working due to:
- Mechanical failure
- Power outage affecting outdoor unit
- Physical damage (like fallen branches)
2. Extreme Cold Temperatures
When outdoor temperatures drop below 25°F (-4°C), most heat pumps struggle to extract sufficient heat from outdoor air. At these temperatures, emergency heat becomes necessary.
3. Heat Pump Freeze-Up
During ice storms or heavy snow, your heat pump may ice over. Signs include:
- Reduced airflow
- Strange noises
- Ice buildup on outdoor unit
When NOT to Use Emergency Heat
Avoid using emergency heat in these situations:
1. Regular Cold Weather
For temperatures above 25°F, your heat pump should operate normally. The thermostat controls will automatically use auxiliary heat when needed.
2. As a Primary Heat Source
Emergency heat costs 2-3 times more to operate than normal heat pump operation. According to U.S. Department of Energy, resistance heating can triple your energy bills.
3. For Extended Periods
Never leave emergency heat on for more than a few days. Continuous use strains system components and leads to premature failure.
Emergency Heat vs. Auxiliary Heat
| Feature | Emergency Heat | Auxiliary Heat |
|---|---|---|
| Activation | Manual | Automatic |
| Temperature Trigger | Below 25°F or system failure | When heat pump can’t maintain 2-3°F difference |
| Energy Cost | Very High | Moderate |
| Duration | Temporary (until repair) | Short cycles |
Proper Emergency Heat Usage
Follow these steps when using emergency heat:
- Confirm the need (system failure or extreme cold)
- Switch thermostat to “Em Heat” mode
- Contact an HVAC professional immediately
- Return to normal operation after repair
Energy Saving Tips
While using emergency heat:
- Lower thermostat to 68°F or below
- Use supplemental heating in occupied rooms
- Seal drafts around windows and doors
System Maintenance
Prevent unnecessary emergency heat use with proper maintenance:
- Schedule annual HVAC inspections
- Keep outdoor unit clear of snow/ice
- Replace air filters monthly
- Consider a heat pump cover in winter
When to Call a Professional
Contact an HVAC technician if:
- Emergency heat runs continuously
- System won’t switch back to normal mode
- You notice strange smells or noises
- Energy bills spike unexpectedly
