Mac fan curves: what the points actually control

Read a curve as a policy, not a promise

The horizontal axis is temperature. The vertical axis is a percentage of the fan’s controllable range. A point at 68 °C and 44% means: when the selected sensor is at that temperature, calculate a target 44% of the way from that fan’s reported minimum RPM to its reported maximum RPM. It does not mean 44% of zero-to-maximum RPM, and it is not a claim about the temperature your Mac will reach.

target RPM = minimum RPM + (maximum RPM − minimum RPM) × curve percentage

Smart Breeze calculates the target independently for every discovered fan, because two fans can report different bounds. The dashboard keeps three different ideas visible: the requested target, the actual live RPM, and who currently owns control. That distinction matters. Drawing a line on a chart is not the same as proving that the hardware followed it.

What happens between the set points

The line between two points is meaningful. Smart Breeze linearly interpolates the fan percentage instead of jumping from one point to the next. On the Balanced adapter example, a temperature between 68 °C and 80 °C produces a percentage between 44% and 72%. This creates a gradual request whose slope is set by the spacing of the points.

Activation and release are deliberately different

Smart Boost does not take control simply because a profile is selected. It watches under System until the controlling sensor crosses the curve’s first temperature point. When it engages, Build 22 will not begin below the fan speed macOS was already requesting, and it does not step its target down while the same Smart Boost session remains engaged.

1. Below the first curve point, macOS keeps control.
2. At or above the first point, Smart Boost requests the interpolated, bounded target and verifies control.
3. If the temperature falls a little, the target does not chase every small reading downward.
4. The sensor must fall below the first point minus the hysteresis value, then remain there for the cooldown period.
5. Smart Breeze requests and verifies a complete System handoff; macOS owns the fans again.

One profile contains separate adapter and battery curves

Smart Breeze stores independent points for power-adapter and battery operation and switches curves when the Mac’s power source changes. That prevents one compromise curve from silently standing in for two different operating contexts. It also means a useful comparison must record whether the Mac was plugged in.

The curve sits inside stricter boundaries

A custom line cannot remove Build 22’s hardware allowlist, fan-reported RPM clamps, System fallback, command expiry, readback checks, or helper watchdog. The helper samples temperature independently. At 95 °C it forces the fans on qualified hardware to their reported maximum; after temperature remains at or below 88 °C for about 20 seconds, it releases the fans to System. That override takes precedence even if a visible curve has a later endpoint.

• App exit, missing data, helper errors, and failed control verification request a System handoff.
• A substantial target write is not presented as successful merely because a command was sent; helper and SMC state are read back.
• Each request is clamped to the minimum and maximum reported by that specific fan.
• Fanless and unqualified models cannot turn a saved curve into fan writes in the public build.

A practical first use

1. Confirm the exact model identifier. Build 22 fan control is qualified only on Mac16,7.
2. Start in System and record one repeatable workload in the 15-minute history.
3. Choose Balanced before editing points. Confirm the selected sensor, power source, and controller label.
4. Run the same workload and compare the target/actual relationship and the System handoff, not only the peak temperature.
5. Create a Custom profile only if you can name the behavior you are trying to change and test one adjustment at a time.

If your Mac is not Mac16,7, the right next step is monitoring or exact-model hardware testing, not attempting to bypass the gate. See how to set a custom curve for the editing workflow, or compare automatic curves with fixed RPM before choosing a mode.