diff --git a/config/example-extras.cfg b/config/example-extras.cfg
index 0e712f7e..97183b7c 100644
--- a/config/example-extras.cfg
+++ b/config/example-extras.cfg
@@ -29,7 +29,8 @@
 
 # Heater cooling fans (one may define any number of sections with a
 # "heater_fan" prefix). A "heater fan" is a fan that will be enabled
-# whenever its associated heater is active.
+# whenever its associated heater is active. In the event of an MCU
+# software error the heater_fan will be set to its max_power.
 #[heater_fan my_nozzle_fan]
 # See the "fan" section for fan configuration parameters.
 #pin: ar4
@@ -40,6 +41,10 @@
 #heater_temp: 50.0
 #   A temperature (in Celsius) that the heater must drop below before
 #   the fan is disabled. The default is 50 Celsius.
+#fan_speed:
+#   The fan speed (expressed as a value from 0.0 to 1.0) that the fan
+#   will be set to when its associated heater is enabled. The default
+#   is max_power.
 
 
 # Additional micro-controllers (one may define any number of sections
diff --git a/klippy/fan.py b/klippy/fan.py
index 3f9bd63d..5401c5ec 100644
--- a/klippy/fan.py
+++ b/klippy/fan.py
@@ -39,6 +39,10 @@ class PrinterHeaterFan:
         heater = config.get("heater", "extruder0")
         self.heater = extruder.get_printer_heater(printer, heater)
         self.heater_temp = config.getfloat("heater_temp", 50.0)
+        max_power = self.fan.max_power
+        self.fan_speed = config.getfloat(
+            "fan_speed", max_power, minval=0., maxval=max_power)
+        self.fan.mcu_fan.setup_shutdown_value(max_power)
         printer.reactor.register_timer(self.callback, printer.reactor.NOW)
     def callback(self, eventtime):
         current_temp, target_temp = self.heater.get_temp(eventtime)
@@ -47,7 +51,7 @@ class PrinterHeaterFan:
             return eventtime + 1.
         power = 0.
         if target_temp or current_temp > self.heater_temp:
-            power = 1.
+            power = self.fan_speed
         print_time = self.mcu.estimated_print_time(eventtime) + FAN_MIN_TIME
         self.fan.set_speed(print_time, power)
         return eventtime + 1.