Heat Pumps
Heat Pump Aux Heat Running Too Much Ontario 2026: Diagnosis, Thermostat Settings, and When to Call the Installer
A heat pump that leans on auxiliary heat at mild winter temperatures is one of the most common complaint patterns in Ontario retrofits. Electricity bills spike, or in a dual-fuel setup the backup furnace runs constantly, and the operating-cost math that justified the conversion collapses. This guide lays out what aux heat is, when it should run, the six root causes ranked by frequency, and the thermostat settings a homeowner can verify before calling the installer back.
Key Takeaways
- Aux heat should run only during defrost cycles and when outdoor temperature is below the heat pump's balance point (typically -10 to -25 Celsius on cold-climate units).
- The single most common cause in Ontario is an accidentally activated emergency heat mode that a homeowner clicked during a cold snap and forgot to switch back.
- The second most common cause is an aggressive overnight setback that triggers aux heat during morning recovery.
- Factory-default balance point on many smart thermostats is -1 Celsius, which is far too warm for a cold-climate heat pump; set it to the manufacturer's minimum operating temperature.
- Electric aux heat costs roughly 2.5 to 3 times more per unit of delivered heat than the heat pump itself at mild winter temperatures.
- If aux heat runtime exceeds 15 to 20 percent of heating hours in any month averaging above -10 Celsius, call the installer back under warranty.
- Ontario 2026 pricing: thermostat reconfiguration free to $250, outdoor sensor replacement $120 to $250, full service visit $180 to $300.
What Aux Heat Is and When It Should Run
Auxiliary heat is the backup heat source built into a heat pump system. In a full-electric installation, aux heat is typically a bank of electric resistance strips inside the air handler that engage when the heat pump cannot meet the thermostat's call for heat. In a dual-fuel setup, aux heat is the backup gas furnace, and the heat pump hands the load off entirely when outdoor temperature drops below a configured cutover point.[1]
Aux heat is engineered to run in only two situations. The first is during a defrost cycle, when the outdoor coil has accumulated frost and the system briefly reverses the refrigerant cycle to shed ice. During this cycle (typically three to ten minutes), cold air is blown indoors from the reversed coil, and a short burst of aux heat keeps supply air temperatures comfortable. Defrost cycles happen every 35 to 90 minutes when outdoor temperature sits between -5 and +5 Celsius and humidity is high.[3]
The second situation is sustained cold weather below the heat pump's balance point. Balance point is the outdoor temperature at which the heat pump's heating capacity exactly matches the home's heat loss. Above balance point, the heat pump alone keeps up. Below, aux heat supplements or (on a dual-fuel system) takes over entirely. On a current cold-climate heat pump, balance point is typically -10 to -25 Celsius; on a mid-tier unit it may be -5 to -10 Celsius.[2]
What Aux Heat Should Not Do
Aux heat should not dominate the monthly heating bill. It should not run constantly at outdoor temperatures above -10 Celsius. It should not run alongside the compressor for hours at a time at mild temperatures. It should not kick in every morning during normal thermostat recovery. And it should not appear on the thermostat's usage chart as a larger share of runtime than the heat pump itself except during genuine cold snaps.
When any of these patterns show up in an Ontario home running a cold-climate heat pump, something is wrong. The equipment may be fine, the installation may be fine, but the configuration or control settings have slipped. The six root causes below cover the overwhelming majority of Ontario cases.
The Six Root Causes Ranked by Ontario Frequency
In order of how often each shows up in Ontario retrofit complaints, with notes on how to spot each one:
| # | Root Cause | Fingerprint | Fix Path |
|---|---|---|---|
| 1 | Thermostat stuck in emergency heat mode | Thermostat display reads “EM HEAT” or “AUX” instead of “HEAT” | Switch mode back to HEAT in thermostat settings |
| 2 | Aggressive overnight setback triggering recovery aux | Aux heat spikes every morning for 30 to 90 minutes | Narrow setback to 2 to 3 degrees, switch recovery mode to eco |
| 3 | Balance point set too warm (factory default) | Aux heat runs every day outdoor temperature drops below 0 Celsius | Reconfigure balance point to manufacturer's minimum operating temp |
| 4 | Defective outdoor temperature sensor | Thermostat reads outdoor temp 5 to 10 degrees below reality | Replace outdoor sensor or switch to internet-sourced outdoor temp |
| 5 | Undersized heat pump for the home | Aux heat on every mild day, especially after sunset | Rarely reparable; supplement with secondary heat source or accept |
| 6 | Compressor or refrigerant problem reducing capacity | Aux heat increasing over time; longer cycle times | Installer diagnostic, possibly refrigerant recharge or compressor repair |
Causes 1 and 2 together account for roughly half of all complaints. Cause 3 is the sleeper: a lot of Ontario installs in the 2022 to 2024 rebate boom went in on Ecobee, Nest, or Honeywell thermostats with factory defaults never adjusted by the installer, and the homeowner discovers the problem the first winter.[4]
How to Diagnose at Home
Before calling the installer, an Ontario homeowner can reasonably check the following in an afternoon:
- Check thermostat mode.On an Ecobee, the main screen shows a mode selector near the temperature reading. Nest shows the mode in settings. Honeywell T-series shows the mode at the bottom of the main display. The correct mode for normal operation is “Heat” or “Auto,” not “Emergency Heat” or “Aux Only.”
- Check aux heat runtime in the thermostat app. Ecobee's HomeIQ report breaks down runtime by stage (compressor vs aux) and by day. Nest's home report shows similar data monthly. Pull up last month and check the aux hours against heat pump hours. If aux is more than a small fraction of heat pump hours during mild weather, confirm the problem is real before troubleshooting.
- Verify outdoor sensor accuracy.Put a reliable outdoor thermometer in the same general location as the heat pump's outdoor sensor (or, if the thermostat is using an internet weather feed, check the feed location is a nearby station). A sensor reading 5 or 10 degrees low will force aux heat on unnecessarily.
- Confirm the outdoor fan spins in heating mode. With the system calling for heat, the outdoor unit's fan should be running. If it is not, the unit may be in defrost, stuck, or failed, and aux is covering the gap. Note: it is normal for the outdoor fan to pause during a defrost cycle for a few minutes.
- Listen for normal defrost cycles. When outdoor temperature is between -5 and +5 Celsius with humidity, the outdoor unit should enter a defrost cycle roughly every 35 to 90 minutes. The cycle lasts three to ten minutes, during which the outdoor fan may stop and indoor supply air briefly drops in temperature before aux stabilizes it. This is normal and brief. A system defrosting every ten minutes or stuck in defrost is not.
Thermostat Settings to Verify
Three settings on the thermostat drive most of the correctable cases. Each is adjustable by the homeowner on Ecobee, Nest, and Honeywell smart thermostats, though the exact menu path varies.
Balance point (also called compressor lockout or aux cutover). Set this to the heat pump manufacturer's minimum operating temperature. Find the spec in the heat pump installation manual or on the manufacturer's product data sheet, typically listed as “minimum outdoor operating temperature” or “heating operating range low.” On a current cold-climate unit this is usually -15 to -25 Celsius. On a mid-tier unit, -5 to -10 Celsius. The factory-default on Ecobee and Nest is often around -1 Celsius, which is wrong for almost every cold-climate system in Ontario.[5]
Recovery mode.Set this to “eco,” “minimal,” or the equivalent “gradual” option. The alternative “aggressive” or “comfort” mode tells the thermostat to hit the setpoint as quickly as possible, which means calling aux heat in during morning ramp-up. Eco mode ramps up gradually using only the heat pump unless outdoor conditions require aux.
Emergency heat. Confirm it is off. On most smart thermostats this is a selectable mode rather than a permanent setting, but it is easy to activate by accident during a cold snap (the thermostat often suggests it on very cold mornings). Once activated, it stays on until the homeowner changes it back to normal heat mode.
Ontario 2026 Pricing
When the problem turns out to require parts or a service visit rather than homeowner reconfiguration, current Ontario price ranges are:
| Work | Typical Ontario Range (2026) | Notes |
|---|---|---|
| Thermostat reconfiguration (homeowner) | Free | 15 minutes if documentation is on hand |
| Thermostat reconfiguration (installer visit) | $150 to $250 | Often covered under installation warranty first year |
| Outdoor temperature sensor replacement | $120 to $250 | Parts and labour combined |
| Service visit and refrigerant charge check | $180 to $300 | Diagnostic only; repair extra |
| Compressor repair or replacement | $1,800 to $4,000 | Often near end-of-life decision territory |
| Replacement of undersized heat pump | $4,000 to $8,000 above original install cost | Rarely economic; supplement instead (wood stove, zone heater) |
The cheapest and most common fix is the first one: the homeowner opens the thermostat settings and either clicks emergency heat off, narrows the setback, or adjusts the balance point. That single afternoon of reconfiguration often eliminates the problem entirely.[6]
The Ontario Economic Math
Electric resistance aux heat runs at a coefficient of performance of 1.0: one kilowatt-hour of electricity in becomes one kilowatt-hour of heat out. A cold-climate heat pump at mild winter temperatures (0 to +5 Celsius) runs at a coefficient of performance of 2.5 to 3.0. At -10 Celsius a good cold-climate unit still delivers 2.0 or better.[2]
At Ontario's current residential electricity prices (roughly $0.10 to $0.19 per kilowatt-hour depending on time-of-use period), the cost of a kilowatt-hour of heat from aux is 2.5 to 3.0 times the cost of the same heat from the compressor. Across an Ontario heating season with moderate aux reliance, that translates to roughly $400 to $900 in excess electricity cost per year on a typical detached home.[7]
On a dual-fuel system, the math is different but the principle is the same: if the backup furnace is running at outdoor temperatures above the cutover point it is programmed to hand off, the home is burning more gas than the retrofit was supposed to eliminate. Either way, a heat pump retrofit that relies on aux heat above -5 Celsius is failing to deliver the operating-cost benefit that justified the capital cost of the conversion.
When to Call the Installer Back
Use this threshold: if aux heat runs more than roughly 15 to 20 percent of heating hours in any month where the average outdoor low is above -10 Celsius, something is wrong. Pull the aux-vs-heat-pump breakdown from the thermostat app, document the monthly split, and contact the installer.
A reputable Ontario installer will return under the installation warranty to reconfigure the thermostat or troubleshoot the heat pump. Most installation warranties in Ontario cover workmanship and commissioning for one to two years; the equipment parts warranty runs five to ten years from the manufacturer. If the installer resists, point to the thermostat data, and if necessary reference HRAI's installation and commissioning standard: a properly commissioned cold-climate heat pump should not lean on aux heat during mild winter weather.[4]
If the installer has gone out of business or is otherwise unreachable, a service-only HVAC contractor can perform the same diagnostic work on an hourly basis. Expect $180 to $300 for a diagnostic visit plus parts and repair cost if something physical needs addressing.
Where This Fits in the Buying Process
An aux-heat problem on a recent retrofit is a commissioning and configuration issue, not an equipment choice issue. The right-sizing and product-selection decisions that prevent cause 5 (undersized heat pump) are made earlier. See our oil to heat pump conversion Ontario 2026 guide for the sizing and dual-fuel design questions that come up before installation, our mini-split vs central heat pump Ontario 2026 guide for the architecture decision that affects how aux heat is provisioned, and our thermostat upgrade options Ontario 2026 guide for the controls side of the same system.
Frequently Asked Questions
What is auxiliary heat on a heat pump and when should it run?
Auxiliary heat is the backup heat source on a heat pump system, usually electric resistance strips built into the air handler or the backup gas furnace in a dual-fuel setup. It is engineered to run only in two situations: briefly during a defrost cycle when the outdoor coil sheds ice, and when outdoor temperature drops below the heat pump's balance point (typically -10 to -25 Celsius on cold-climate models). At any outdoor temperature above the balance point, the heat pump alone should handle the load. Aux heat running constantly at mild winter temperatures means something is miswired, misconfigured, or the heat pump is underperforming.
How much aux heat runtime is normal in an Ontario winter?
On a correctly sized cold-climate heat pump with a properly set balance point, aux heat runtime in a typical Ontario winter runs in the low single digits as a percentage of total heating hours. Expect brief spikes during defrost cycles, a sustained contribution on the coldest two to three weeks of the year when outdoor temperature sits below -15 Celsius, and near zero in November, March, and April. If the thermostat app reports aux heat running more than 15 to 20 percent of heating hours in any month where the average overnight low is above -10 Celsius, something is wrong and the installer should come back under warranty.
Why is my aux heat running when it is only zero degrees outside?
The two most common causes are an accidentally activated emergency heat mode on the thermostat and an aggressive overnight setback. Emergency heat forces aux heat on regardless of outdoor conditions and is easy to click by mistake during a cold snap. An aggressive setback (16 Celsius overnight to 21 Celsius in the morning) creates a large temperature swing that the thermostat tries to recover quickly by calling aux heat in. The fix for the first is to switch back to regular heat mode. The fix for the second is to narrow the setback to two or three degrees and use the thermostat's eco or minimal recovery setting rather than aggressive recovery.
What is balance point and how do I set it correctly?
Balance point is the outdoor temperature below which the heat pump alone can no longer keep up with the home's heat loss. Above the balance point, the heat pump handles the load; below, aux heat takes over. Ecobee, Nest, and Honeywell smart thermostats all expose a configurable balance point (sometimes called compressor lockout or aux cutover temperature). The factory default is often -1 Celsius, which is far too warm for a cold-climate heat pump and forces aux heat on every mild winter day. On a current cold-climate unit, the correct setting is the manufacturer's minimum operating temperature, typically -15 to -20 Celsius. Check the heat pump's spec sheet or the installation manual and set the thermostat accordingly.
How much does electric aux heat cost compared to the heat pump itself?
Electric resistance aux heat delivers heat at a coefficient of performance of 1.0; every kilowatt-hour in becomes one kilowatt-hour of heat out. A cold-climate heat pump at mild winter temperatures (say 0 to 5 Celsius) delivers a coefficient of performance of roughly 2.5 to 3.0, meaning every kilowatt-hour in becomes 2.5 to 3.0 kilowatt-hours of heat. At the same electricity rate, the aux heat is 2.5 to 3.0 times more expensive per unit of delivered heat. A retrofit that relies heavily on aux heat above -5 Celsius is not capturing the operating-cost benefit that justified spending ten to twenty thousand dollars on the conversion in the first place.
When should I call the installer back versus trying to fix it myself?
Thermostat settings (balance point, recovery mode, and whether emergency heat is accidentally on) are reasonable to verify at home, and some homeowners will also check outdoor sensor accuracy against a known thermometer. Refrigerant charge, compressor diagnostics, and outdoor unit sensor wiring are installer territory. The simplest rule: verify the thermostat settings and emergency heat status first because these cost nothing to correct. If the settings look right and aux heat is still running excessively, call the installer and invoke the installation warranty. Reputable installers will return to reconfigure or troubleshoot under the original install warranty in the first year, and most offer a longer workmanship window.
Related Guides
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- Mini-Split vs Central Heat Pump Ontario 2026
- Thermostat Upgrade Options Ontario 2026
- Natural Resources Canada Heating and Cooling with a Heat Pump
- ENERGY STAR Canada Air-Source Heat Pumps: Sizing, Controls, and Cold-Climate Performance
- Canadian Heat Pump Coalition Cold-Climate Heat Pump Technical Resources and Installer Guidance
- Heating, Refrigeration and Air Conditioning Institute of Canada (HRAI) Air-Source Heat Pump Installation Standard and Commissioning Guidance
- ASHRAE ASHRAE Handbook: HVAC Applications, Residential Heat Pumps and Controls
- Ontario Energy Board Home Renovation Savings Program: Air-Source Heat Pump Incentives
- Independent Electricity System Operator Residential Electricity Pricing and Time-of-Use Rates
- Enbridge Gas Home Renovation Savings Program: Qualifying Measures and Rebate Amounts