Heat Pump Emergency Heat: When to Use It
What the Em Heat setting really does, how it differs from auxiliary heat, and why heat pump emergency heat is a short-term backup, not an everyday mode.
The short answer: Heat pump emergency heat is a manual thermostat setting that shuts off the outdoor unit and heats your home with backup heat alone, either electric strips or a gas furnace. Auxiliary heat comes on automatically to help the heat pump in deep cold or during defrost. Use emergency heat only when the outdoor unit has failed, and book a repair the same day.
On a bitter morning, the thermostat shows Aux and the house feels cool, so many homeowners press Em Heat expecting faster heat. It is not faster, and it can push your hydro bill higher. This guide helps GTA homeowners, including families in Markham and Richmond Hill, understand their backup heat. If your heat is already off, book a service visit online or call 310-HEAT any time.
Heat Pump Emergency Heat vs Auxiliary Heat: What Is the Difference?
Most air source heat pumps in Ontario have a second heat source. Natural Resources Canada (NRCan) describes electric resistance elements in the ductwork, or a furnace or boiler in a hybrid system. Auxiliary heat and heat pump emergency heat both use that same source. The difference is who is in control.
Auxiliary heat
The helper
- Turns on automatically
- Works alongside the heat pump, or takes over in deep cold
- Shuts off once the heat pump can keep up
- Normal on cold days and during defrost
Emergency heat
The stand-in
- Selected by a person at the thermostat
- Keeps the outdoor unit off completely
- Stays on until someone switches it back
- Meant for a failed or damaged outdoor unit
When Backup Heat Turns On by Itself
Auxiliary heat switches on by itself in four common situations:
- Below the balance point. NRCan defines this as the outdoor temperature where the heat pump's capacity equals your home's heat loss. Below it, stage two calls for supplementary heat.
- During defrost. NRCan notes supplementary heat may be needed while the heat pump defrosts.
- After a big setback. Backup heat runs until the heat pump catches up, which is why NRCan suggests setbacks of no more than 2°C. See our recommended thermostat settings.
- Below the cut-off temperature. NRCan says newer models have minimum operating temperatures between -15°C and -25°C. Below that, an outdoor sensor shuts the heat pump off. Dual-fuel systems often switch earlier, when the furnace is cheaper to run.
That last case can look like heat pump emergency heat, but the system switches back by itself when the weather warms up. Our article on how extreme cold impacts heat pump performance explains more. True emergency heat, on most thermostats, is a manual mode that stays on until someone changes it. If Em Heat is showing and nobody selected it, the outdoor unit may have reported a fault.
Should You Switch to Heat Pump Emergency Heat? Six Situations
| Situation | Switch? | What to do |
|---|---|---|
| The outdoor unit will not run and the house is cooling | Yes, for now | Use Em Heat and book a same-day repair. |
| A branch or roof ice has damaged the unit | Yes | Keep away from the unit and call a technician. |
| Thick ice covers the coil and never melts | Yes, until it is checked | Brush loose snow away by hand, then call. |
| Aux Heat appears on a cold morning | No | This is normal. Leave the thermostat on Heat. |
| Steam and a whoosh for a few minutes | No | It is defrost and ends on its own. |
| You want the house to warm up faster | No | Em Heat is not faster. Raise the setpoint a degree or two at a time. |
A technician may also ask you to run heat pump emergency heat while a part is on order. Once the repair is done, switch back to Heat.
Why Heat Pump Emergency Heat Costs More to Run
A heat pump moves heat rather than creating it. NRCan explains that a heat pump using 1 kW of electricity to move 3 kW of heat has a coefficient of performance (COP) of 3. Electric strips turn each unit of electricity into one unit of heat, and NRCan notes they are less efficient than the heat pump, though they work at any outdoor temperature.
Heat delivered from one kWh of electricity (heat pump ranges from NRCan)
On an all-electric system, heat pump emergency heat often uses two or more times the electricity for the same warmth on a typical winter day.
Timing matters too. The Ontario Energy Board sets rates once a year on November 1. Under prices set for November 1, 2026, Ultra-Low Overnight customers pay 3.7 cents per kWh every day from 11 p.m. to 7 a.m., but 37.7 cents on weekdays from 4 p.m. to 9 p.m. Time-of-Use on-peak is 18.9 cents. Our guide to the ultra-low overnight rate explains which plan suits a heat pump home, and our 100 amp panel heat pump article explains how much current backup strips draw.
Dual Fuel vs Electric Strip Backup
How heat pump emergency heat feels, and what it costs, depends on your backup:
| Electric strip backup | Dual fuel (gas furnace) | |
|---|---|---|
| Where it is | Elements in the air handler or ducts | A gas furnace on the same ducts |
| Runs with the heat pump? | Yes, per NRCan | No, per NRCan |
| On Em Heat | Steady heat, but hydro use climbs fast | Works like a furnace; gas use rises |
| Safety notes | Wiring is for licensed electricians | CO alarms required |
| Common in | Homes without gas service | Homes that kept a gas furnace |
With dual fuel, Ontario requires carbon monoxide alarms adjacent to each sleeping area and, since January 1, 2026, on every storey. If an alarm sounds, get everyone out and call 911 from outside. If you smell rotten eggs, leave the home, then call Enbridge Gas at 1-866-763-5427 or 911 from outside. See our carbon monoxide alarm guide.
Our heat pump installation team can size either backup, and our gas furnace ban article explains why hybrid systems stay popular here.
Relying on Heat Pump Emergency Heat? When to Call a Technician
Book a service visit if any of these sound familiar:
- You had to switch to Em Heat to stay warm.
- Aux Heat runs for hours on mild days above freezing.
- The outdoor fan or compressor will not start in Heat mode.
- Ice covers the coil and does not clear after a defrost cycle.
- Your hydro or gas bill jumps for no clear reason.
- A breaker keeps tripping, or you smell burning.
Typical causes include a failed fan motor or capacitor, low refrigerant, a faulty outdoor sensor, a stuck reversing valve or incorrect thermostat wiring. Refrigerant and electrical repairs are never do-it-yourself jobs. If you see smoke or smell burning, turn the system off at the thermostat and call 911 if there is any sign of fire.
Our heat pump repair guide explains what a diagnostic visit includes, and our article on the three most common heat pump problems covers units that will not start. Do not leave heat pump emergency heat on for weeks: the bill keeps climbing, and a small fault can grow.
Safe Checks Before You Call
None of these involve opening panels or touching wiring:
- Check the mode. Set the thermostat to Heat and replace the batteries if the screen is faint.
- Check the filter. A clogged filter chokes airflow and makes backup heat run longer.
- Clear the outdoor unit. Brush loose snow away by hand. Never chip ice or pour hot water on the coil.
- Open the vents. Keep registers and return grilles open and clear of furniture.
- Look at the breaker panel. Look only. If a heat pump breaker has tripped, call a technician instead of resetting it repeatedly.
If the heat pump still will not run, switch to emergency heat and book a visit.
Heat Pump Help for Markham, Richmond Hill and the GTA
Aire One is a TSSA-registered Carrier Factory Authorized Dealer serving Ontario since 1990, with a 4.8-star Google rating from 541 reviews, 24/7 technicians and a $79 service call. Our heat pump repair technicians can find out why your system leans on backup, and our heat pump specialists can tell you if a cold-climate model makes sense. Learn about our HVAC company in Markham and our HVAC company in Richmond Hill.
The Home Renovation Savings Program from Save on Energy and Enbridge Gas offers up to $7,500 for a qualifying cold-climate air source heat pump, based on size. Amounts can change, so check saveonenergy.ca. We also offer a free Total Home Assessment, financing and a 10-year worry-free warranty, and our maintenance and protection plans include a yearly check of controls and backup heat.
Stuck on heat pump emergency heat?
Our technicians answer 24/7 across Markham, Richmond Hill and the GTA. TSSA-registered and trusted since 1990.
310-HEAT (310-4328) · 24/7 service · $79 service call*
Frequently Asked Questions
Is it bad to run heat pump emergency heat?
It will not harm the system, but it usually costs more because only backup heat is running. Use it when the outdoor unit has failed, book a repair right away, and switch back to Heat afterward.
Should I turn on emergency heat when it is very cold outside?
Usually not. Your system adds auxiliary heat automatically when the heat pump needs help. Leave the thermostat on Heat unless the outdoor unit has stopped working.
Why does my thermostat say Aux Heat?
It means backup heat is helping the heat pump. That is normal on cold days, during defrost and after you raise the setpoint. If it shows for hours on mild days, have the system checked.
Does emergency heat warm the house faster?
No. It simply runs the backup source alone, which usually costs more. Raising the setpoint a degree or two at a time lets the heat pump do most of the work.
How long can I leave heat pump emergency heat on?
As long as you need to stay warm until a technician arrives. It is a temporary backup, so book a repair as soon as you switch to it.
Sources and Helpful Resources
- Natural Resources Canada: Heating and Cooling With a Heat Pump
- Ontario Energy Board: Electricity Rates
- Government of Ontario: Carbon Monoxide Safety
- Save on Energy: Home Renovation Savings Program
Matthew leads the Aire One Markham and Metro Toronto team, helping homeowners stay warm through every Ontario winter. Aire One has been a TSSA-registered, Carrier Factory Authorized Dealer since 1990.