diff --git a/config/example-extras.cfg b/config/example-extras.cfg
index 65d8115b..08fd6c4f 100644
--- a/config/example-extras.cfg
+++ b/config/example-extras.cfg
@@ -211,6 +211,37 @@
 #   is 1.0
 
 
+# Temperature-triggered cooling fans (one may define any number of
+# sections with a "temperature_fan" prefix). A "temperature fan" is
+# a fan that will be enabled whenever its associated sensor is above
+# a set temperature. In the event of an MCU software error the
+# temperature_fan will be set to its max_power.
+#[temperature_fan my_temp_fan]
+# See the "fan" section for fan configuration parameters.
+#pin: ar4
+# See the "heater" section for details about the sensor_type and
+# sensor_pin parameters.
+#sensor_type: EPCOS 100K B57560G104F
+#sensor_pin: analog13
+# The remaining variables are specific to temperature_fan.
+#min_temp: 0
+#max_temp: 100
+#   The maximum range of valid temperatures (in Celsius) that the
+#   sensor must remain within. This controls a safety feature
+#   implemented in the micro-controller code - should the measured
+#   temperature ever fall outside this range then the micro-controller
+#   will go into a shutdown state. Set this range just wide enough so
+#   that reasonable temperatures do not result in an error. These
+#   parameters must be provided.
+#temp: 40.0
+#   A temperature (in Celsius) that the sensor must exceed before the
+#   fan is enabled. The default is 40 Celsius.
+#fan_speed: 1.0
+#   The fan speed (expressed as a value from 0.0 to 1.0) that the fan
+#   will be set to when the sensor temperature exceeds the set value.
+#   The default is 1.0.
+
+
 # Additional micro-controllers (one may define any number of sections
 # with an "mcu" prefix). Additional micro-controllers introduce
 # additional pins that may be configured as heaters, steppers, fans,
diff --git a/klippy/extras/temperature_fan.py b/klippy/extras/temperature_fan.py
new file mode 100644
index 00000000..2c3e0177
--- /dev/null
+++ b/klippy/extras/temperature_fan.py
@@ -0,0 +1,44 @@
+# Support fans that are enabled when temperature exceeds a set threshold
+#
+# Copyright (C) 2016-2018  Kevin O'Connor <kevin@koconnor.net>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+import fan
+
+PIN_MIN_TIME = 0.100
+KELVIN_TO_CELCIUS = -273.15
+
+class TemperatureFan:
+    def __init__(self, config):
+        self.name = config.get_name()
+        self.printer = config.get_printer()
+        self.fan = fan.PrinterFan(config)
+        self.mcu = self.fan.mcu_fan.get_mcu()
+        self.fan_speed = config.getfloat('fan_speed', 1., minval=0., maxval=1.)
+        min_temp = config.getfloat('min_temp', minval=KELVIN_TO_CELCIUS)
+        max_temp = config.getfloat('max_temp', above=min_temp)
+        self.temp = config.getfloat('temp', 40. if max_temp > 40. else max_temp,
+            minval=min_temp, maxval=max_temp)
+        self.fan.set_shutdown_speed(1.)
+        self.last_temp = KELVIN_TO_CELCIUS
+        self.sensor = self.printer.lookup_object('heater').setup_sensor(config)
+        self.sensor.setup_minmax(min_temp, max_temp)
+        self.sensor.setup_callback(self.temperature_callback)
+    def printer_state(self, state):
+        if state == 'ready':
+            reactor = self.printer.get_reactor()
+            reactor.register_timer(self.callback, reactor.NOW)
+    def callback(self, eventtime):
+        power = 0.
+        if self.last_temp > self.temp:
+            power = self.fan_speed
+        print_time = self.mcu.estimated_print_time(eventtime) + PIN_MIN_TIME
+        self.fan.set_speed(print_time, power)
+        return eventtime + 1.
+    def temperature_callback(self, read_time, temp):
+        self.last_temp = temp
+    def stats(self, eventtime):
+        return True, '%s: temp=%.1f' % (self.name, self.last_temp)
+
+def load_config_prefix(config):
+    return TemperatureFan(config)
diff --git a/klippy/heater.py b/klippy/heater.py
index 7c0def43..4591b2b4 100644
--- a/klippy/heater.py
+++ b/klippy/heater.py
@@ -206,13 +206,7 @@ class PrinterHeaters:
         if heater_name in self.heaters:
             raise config.error("Heater %s already registered" % (heater_name,))
         # Setup sensor
-        self.printer.try_load_module(config, "thermistor")
-        self.printer.try_load_module(config, "adc_temperature")
-        sensor_type = config.get('sensor_type')
-        if sensor_type not in self.sensors:
-            raise self.printer.config_error("Unknown temperature sensor '%s'" % (
-                sensor_type,))
-        sensor = self.sensors[sensor_type](config)
+        sensor = self.setup_sensor(config)
         # Create heater
         self.heaters[heater_name] = heater = Heater(config, sensor)
         return heater
@@ -223,6 +217,14 @@ class PrinterHeaters:
             raise self.printer.config_error(
                 "Unknown heater '%s'" % (heater_name,))
         return self.heaters[heater_name]
+    def setup_sensor(self, config):
+        self.printer.try_load_module(config, "thermistor")
+        self.printer.try_load_module(config, "adc_temperature")
+        sensor_type = config.get('sensor_type')
+        if sensor_type not in self.sensors:
+            raise self.printer.config_error("Unknown temperature sensor '%s'" % (
+                sensor_type,))
+        return self.sensors[sensor_type](config)
 
 def add_printer_objects(printer, config):
     printer.add_object('heater', PrinterHeaters(printer, config))