What is Honeywell Balance Point / Compressor Lockout?

The outdoor temperature below which the heat pump compressor stops and your furnace or other heat takes over. On the T6 Pro it is ISU 355; on the T10/T10+ it is part of ISU 3120, Equipment Lockouts.

What should Honeywell Aux Heat Lockout be set to?

At or above your compressor lockout. On a dual-fuel system, set both from your heatpump.blue result; on electric-strip backup, set compressor lockout to Off and aux heat lockout a few degrees above where your heat pump stops keeping up.

Where are the T9's lockout settings?

We could not find them documented in Resideo's public manuals. Check your T9's installer setup menu directly, or contact Resideo support — the general rules on this page (aux at or above compressor lockout, a real outdoor temperature source) still apply.

Thermostat settings

Honeywell heat pump lockout settings

Honeywell (Resideo) thermostats set the lockouts in an installer setup (ISU) menu, by number. The ISU numbers differ by model; this page covers the T6 Pro Smart, the non-Wi-Fi T6 Pro, the T10/T10+ Pro and the older VisionPRO 8000/Prestige. We could not find the T9's lockout settings in Resideo's public documents — check your T9's installer manual.

Where to find it

T6 Pro Smart / T6 Pro (Wi-Fi): press and hold Menu for 5 seconds → Device Setup. Non-Wi-Fi T6 Pro: hold the center and arrow buttons about 3 seconds, then Select. T10/T10+ Pro: Menu → Thermostat Information (note the date code) → back → Installer Options → enter the date code → Installer Setup.

T6 Pro Smart (TH6220WF2006, TH6320WF2003) and non-Wi-Fi T6 Pro

ISU 355 only appears once an outdoor temperature source is set (ISU 130) and the thermostat — not an external fossil-fuel kit — controls the furnace or other heat.

T6 Pro Smart (TH6220WF2006, TH6320WF2003) and non-Wi-Fi T6 Pro lockout settings
Setting	What it does	Values
ISU 130 Outdoor Temp	Outdoor temperature source.	No, Wired, Internet (a wired sensor is recommended).
ISU 255 Aux Heat Type	Whether the other heat is electric or a fossil-fuel furnace (dual fuel).	Electric, or Gas/Oil.
ISU 355 Balance Point (Compressor Lockout)	Compressor (heat pump) lockout.	Off, or 5–60 °F in 5 °F steps. Default 40 °F on dual fuel, Off with electric aux.
ISU 356 Aux Heat Lock Out	Aux/furnace lockout.	Off, or 5–65 °F in 5 °F steps.

T10 / T10+ Pro

T10 / T10+ Pro lockout settings
Setting	What it does	Values
ISU 3120 Equipment Lockouts — Compressor Lockout/Balance Point	Compressor lockout.	Off, or −15 to 50 °F (steps not stated).
ISU 3120 — Backup Heat Lockout	Backup lockout.	Off, or 5 to 65 °F (steps not stated).
ISU 1060 Outdoor temperature	Outdoor temperature source.	Wired C7089U1006, wireless sensor on T10+, or internet.

VisionPRO 8000 / Prestige (older models)

Source is a 2006 pocket guide; requires an outdoor sensor (ISU 0340 = 2).

VisionPRO 8000 / Prestige (older models) lockout settings
Setting	What it does	Values
0350 Heat pump compressor lockout	Compressor lockout.	Off, or 15, 20, 25, 30, 35, 40 °F.
0360 Heat pump auxiliary lockout	Aux/furnace lockout.	Off, or 40, 45, 50, 55, 60 °F.

How your heatpump.blue result maps onto this

heatpump.blue finds the outdoor temperature below which your furnace or other heat costs less than running the heat pump, for your weather, your model and your rates. On Honeywell, that number goes into the setting below.

Dual fuel: set Compressor Lockout / Balance Point to your heatpump.blue recommendation, rounded to the nearest 5 °F step (or Off for "never lock out"). Set the Aux/Backup Heat Lockout at or above it.
Electric strips: set Compressor Lockout to Off, and set the Aux Heat Lockout a few degrees above the temperature where your heat pump stops keeping up with your home.

Get your Honeywell number

Enter your ZIP, your heat pump model and your rates, and get the lockout temperature that costs you least, with the range it is sensitive to.

Open the tool

Common mistakes

Setting a lockout without first setting Outdoor Temp (ISU 130) or the T10's outdoor source (ISU 1060) to a real source — the lockout fields need an outdoor reading to act on.
Expecting exact ranges and steps on the T10/T10+ or VisionPRO lines, which Resideo's current documents don't fully state — round to the nearest value your unit accepts.
Setting the aux/furnace lockout below the compressor lockout. That leaves a band of outdoor temperatures where nothing is allowed to run. Keep the aux/furnace lockout at or above the compressor lockout.
Changing the setting without writing down the factory default first. These are installer menus; changing them is safe, but you may want to undo it.
Assuming the factory default is the cheapest setting for your home. It is a generic default, not calculated for your climate, your model or your energy rates.
Forgetting the setting needs an outdoor temperature source (a wired sensor, a communicating outdoor unit, or internet weather) to do anything at all.

Questions

What is Honeywell Balance Point / Compressor Lockout?: The outdoor temperature below which the heat pump compressor stops and your furnace or other heat takes over. On the T6 Pro it is ISU 355; on the T10/T10+ it is part of ISU 3120, Equipment Lockouts.
What should Honeywell Aux Heat Lockout be set to?: At or above your compressor lockout. On a dual-fuel system, set both from your heatpump.blue result; on electric-strip backup, set compressor lockout to Off and aux heat lockout a few degrees above where your heat pump stops keeping up.
Where are the T9's lockout settings?: We could not find them documented in Resideo's public manuals. Check your T9's installer setup menu directly, or contact Resideo support — the general rules on this page (aux at or above compressor lockout, a real outdoor temperature source) still apply.

Sources

Checked against the manufacturer’s own documents on 2026-10-08. Firmware and documents change; your model’s current installer manual wins over this page.