Heat Pump Aux Heat Lockout Temperature Ontario 2026: What It Is, Why It Matters, and How to Set It

What Aux Heat Actually Is

A heat pump moves heat from outdoors to indoors using a refrigerant cycle. It does not burn fuel and it does not make heat the way a furnace or a toaster does. On a mild Ontario day it is remarkably efficient, delivering roughly two to four units of heat for every unit of electricity it consumes.[1]On a very cold day the outdoor coil has less heat available to move, the compressor works harder, and at some point the unit can no longer meet the house heat loss on its own. That is where auxiliary heat steps in.

Auxiliary heat is a second, separate heat source wired to the same thermostat. On an all-electric Ontario install it is almost always a bank of resistance strip heaters sitting in the air handler downstream of the indoor coil. On a dual-fuel install it is the existing gas furnace. On a packaged rooftop or cold-climate unit it can be electric element heat inside the outdoor cabinet. In every case the thermostat brings it on only when the heat pump alone is not keeping up.[3]

The Economics: Why Lockout Matters

The entire reason the lockout setting exists is economic. Electric strip heat runs at a coefficient of performance of exactly 1.0, one unit of heat for one unit of electricity, because resistance heating cannot be more efficient than that. A modern cold-climate inverter heat pump typically holds a coefficient of performance between 1.8 and 2.5 at minus 15 Celsius, and between 1.3 and 1.8 at minus 25 Celsius, depending on the model.[2]That means strip heat costs roughly two to four times more per unit of delivered heat than the heat pump, at the same Ontario electricity rate.

Letting strips run at minus 5 Celsius instead of the heat pump wastes roughly 60 to 70 percent of the dollar. Letting strips run at plus 5 Celsius wastes close to 70 percent. Over a full Ontario heating season, setting the lockout conservatively warm (aux allowed above minus 2 Celsius, say) can easily add $300 to $600 to the electricity bill on a typical detached home, compared to a properly tuned lockout.[1]The symmetric failure mode, a lockout set too cold, means the house slowly drops below setpoint on a real cold snap because aux never engages when it is actually needed. That is a comfort problem, not a cost problem, but it is just as real.

Manufacturer Defaults vs Ontario Reality

Out of the box, most thermostats ship with conservative defaults that assume a warmer climate than Ontario winter actually delivers. Honeywell T-series often defaults to a balance point around 35 Fahrenheit (roughly plus 1.5 Celsius). Ecobee defaults Aux Heat Max Outdoor Temp to 50 Fahrenheit (10 Celsius). Nest learns over time but often biases toward aux during the first Ontario winter if the homeowner is not watching.[6]Those defaults are safe, because they guarantee the house reaches setpoint on every cold day. They are also expensive because they let strip heat run on mild days when the heat pump is perfectly capable.

These are starting points, not prescriptions. The right lockout temperature for any specific home depends on the heat pump model capacity curve at low outdoor temperatures, the measured or estimated house heat loss, the backup type, and local electricity and gas rates. The manufacturer performance data submitted to AHRI is the authoritative source for the capacity curve.[5]A proper commissioning visit computes the balance point (where heat pump output equals house heat loss) and sets the lockout a few degrees above or below that balance point, depending on the backup type and cost structure.[6]

How to Set It on Ecobee, Honeywell, and Nest

Ecobee (3, 4, Smart Thermostat Premium, Enhanced)

Hold the main menu icon (five dots) to unlock the installer path, select Installation Settings, Thresholds. Two relevant values:

• Compressor Min Outdoor Temp: the coldest outdoor temperature the heat pump is allowed to run at. Set this to the manufacturer minimum (often minus 25 Celsius for cold-climate units, minus 15 for mid-tier, minus 10 for older single-stage).
• Aux Heat Max Outdoor Temp: the warmest outdoor temperature aux is allowed to run at. Set this to the target lockout from the table above (minus 15 for cold-climate, minus 10 to minus 12 for dual-fuel).

Ecobee calls the difference between these two values the aux heat zone, which is the window where both the heat pump and aux can cooperate.

Honeywell T-series, VisionPro, T10, T9

Honeywell uses the term Balance Point. Enter the installer menu (typically hold Menu plus the lower-right key for five seconds, or enter the date code on newer models), select Installer Options, Balance Points. Two relevant values:

• Low Balance Point: the outdoor temperature below which the heat pump is locked out and aux takes over entirely (used mostly in dual-fuel setups with a gas furnace). Set this to the target lockout for the heat pump itself.
• High Balance Point: the outdoor temperature above which aux is locked out entirely (used mostly in all-electric setups). Set this to the target aux lockout.

On an all-electric Ontario install the High Balance Point is the setting that matters. On a dual-fuel install the Low Balance Point is the setting that matters.

Google Nest Learning Thermostat, Nest Thermostat (3rd/4th gen)

Nest hides the equivalent setting under Equipment, Heat Pump Balance. The options are Max Savings, Balanced, and Max Comfort. Each setting is mapped internally to a different balance point behaviour, not a specific outdoor temperature. Max Savings keeps aux off as long as possible; Max Comfort brings aux in earlier to guarantee setpoint. On a cold-climate inverter system in Ontario, Max Savings is usually the right starting position. Nest also supports an installer-only Lockout Temperature on some pro-installed models; a qualified contractor can surface that setting if the heat pump has a clearly defined minimum operating temperature that differs from the default.

The Emergency Heat Button

Most heat pump thermostats have an Emergency Heat mode accessible from the home screen. This is not a cold-weather setting. It forces the thermostat to run aux heat only and leaves the heat pump compressor off entirely. The use case is narrow: the heat pump has failed (compressor out, refrigerant lost, outdoor unit iced over and undefrostable) and a technician is on the way. Until the tech arrives, Emergency Heat keeps the house warm on strips or the gas furnace.[6]

Running on Emergency Heat through an Ontario winter week can add several hundred dollars to an electricity bill on an all-electric system. It also masks the underlying failure, which can turn a one-day service call into a months-long misdiagnosis. If Emergency Heat ever gets turned on, book the service call the same day.

Signs the Lockout Is Wrong

Three symptom patterns usually point to a lockout set incorrectly. None of them require test equipment to spot.

• Electricity bill spike in December or January. A bill two to four times the October baseline on an all-electric heat pump is almost always strips running too often, which points to the lockout set too warm.
• Aux Heat indicator on at mild temperatures. The thermostat showing Aux Heat for hours at outdoor temperatures around zero Celsius means aux is engaging when the heat pump could carry the load. Lockout is set too warm.
• House under setpoint on a cold snap. Indoor temperature drifting two to four Celsius below setpoint during a minus 20 stretch, with the heat pump still running but aux never coming on, points to the lockout set too cold.

The Consumer Protection Ontario framework gives homeowners a clear path if a contractor installed a heat pump and never commissioned the controls (a common source of never-tuned lockout settings). Commissioning is a standard part of a professional install, and an installer who delivered an untuned system is a reasonable target for a follow-up call at no additional charge.[8]

How to Test a New Setting

After adjusting the lockout, the test is straightforward. Wait for a cold day, ideally one within 3 Celsius of the new lockout temperature, and watch the thermostat:

1. Confirm the outdoor temperature on the thermostat (or a reliable local reading).
2. Confirm the heat pump is running (outdoor fan on, indoor fan on, thermostat showing Heat not Aux Heat).
3. Confirm the indoor temperature holds setpoint for at least two hours without aux engaging.
4. If the house drops more than 1 Celsius below setpoint without aux engaging, raise the lockout by 3 to 5 Fahrenheit (roughly 2 Celsius) and retest.
5. If aux engages but the house was already at setpoint with only the heat pump, lower the lockout by 3 to 5 Fahrenheit and retest.

Ontario design temperatures vary by zone: Toronto design is roughly minus 18 Celsius, Ottawa is closer to minus 24, and north of the 45th parallel the design temperature can reach minus 30. The lockout should be tested at or near the design temperature to prove out the cold snap case.[4]

Pro Setup in Ontario 2026: What It Costs

If a homeowner does not want to touch the installer menu, a contractor visit dedicated to commissioning the heat pump controls typically runs $120 to $180 in the GTA and most Ontario markets. Many contractors include lockout tuning as part of an annual maintenance tune-up ($150 to $220), so timing the commissioning visit to coincide with the first fall tune-up usually gets it done at no incremental cost.[3]

A handful of Ontario utility programs, including the IESO Home Renovation Savings program and select Enbridge incentives, have supported qualifying heat pump installations with per-measure incentives during 2025 and into 2026. Program terms shift, so the specific rebate status at the time of install should be verified with the administrator.[7]Commissioning itself is typically not rebate-eligible, but a rebate-eligible install should include commissioning as part of the installer scope; ask for it explicitly on the quote.

Putting It All Together

1. Identify the heat pump type (cold-climate inverter, mid-tier two-stage, or older single-stage).
2. Identify the backup type (electric resistance strips, gas furnace in dual-fuel, or packaged element heat).
3. Pick the starting lockout from the Ontario reality table above.
4. Locate the setting on the thermostat (Ecobee Thresholds, Honeywell Balance Points, Nest Heat Pump Balance).
5. Enter the new value in the installer menu.
6. Wait for a cold day near the design temperature and run the five-step test.
7. Adjust by 3 to 5 Fahrenheit increments if aux engages when the heat pump alone could carry the load, or if the house does not hold setpoint.
8. Log the December and January electricity bill and compare year over year; a properly tuned lockout usually shows up as a $300 to $600 reduction on an all-electric detached home.

The setting is small, the installer menu is intimidating, and the savings are real. Ten minutes of tuning plus one cold-day test is the shortest path to making an Ontario heat pump pay for itself through a real winter.

Frequently Asked Questions

Related Guides

• Heat Pump Aux Heat Running Too Much Ontario 2026
• Dual-Fuel Hybrid Heat Pump and Furnace Ontario
• Heat Pump Cold Climate Thresholds Ontario 2026