diff --git a/brewpi/brewpi.py b/brewpi/brewpi.py
index 3a829d6..29b1fd2 100755
--- a/brewpi/brewpi.py
+++ b/brewpi/brewpi.py
@@ -29,6 +29,7 @@ if __name__ == '__main__':
 	DT = config['Controller']['dt']
 	DT_TASK = 1.0 / config['Controller']['sim_warp_factor']
 	DT_TASK_TRACER = DT_TASK / DT
+	theta_amb = config['ambient_temperature']
 
 	# Sensor
 	sensor = TempSensorFactory.create(config['Controller']['sensor_name'], temp_offset=-0.15, variance=0.01)
@@ -37,7 +38,7 @@ if __name__ == '__main__':
 
 	# Plant
 	pot_params = config['Plant']
-	pot = Pot(DT, pot_params, 20)
+	pot = Pot(DT, pot_params, theta_amb)
 	taskmgr.add(PotTask(pot, DT_TASK, dispatcher.msgio_get("Pot")))
 
 	# Heater
@@ -47,7 +48,7 @@ if __name__ == '__main__':
 	taskmgr.add(heater_task)
 
 	# Temperature Controller
-	tc = PidFactory.create(config['Controller']['pid_type'], DT, config['TempCtrl'], config['Model'])
+	tc = PidFactory.create(config['Controller']['pid_type'], DT, config['TempCtrl'], config['Model'], theta_amb=theta_amb)
 	tc_task = TcTask(tc, DT_TASK, dispatcher.msgio_get("TempCtrl"))
 	taskmgr.add(tc_task)
 
diff --git a/components/pid/temp_controller_smith.py b/components/pid/temp_controller_smith.py
index 39ef492..ee336fb 100755
--- a/components/pid/temp_controller_smith.py
+++ b/components/pid/temp_controller_smith.py
@@ -3,7 +3,7 @@ from components.pid.temp_controller_base import TempControllerBase, States
 
 
 class TempController(TempControllerBase):
-	def __init__(self, dt, params, model_params):
+	def __init__(self, dt, params, model_params, theta_amb=20):
 		TempControllerBase.__init__(self, dt, params)
 		self.dt = dt
 		self.last_theta_ist = 20
@@ -11,10 +11,10 @@ class TempController(TempControllerBase):
 
 		# Fast model: same plant model but with zero transport delay, used
 		# to predict the current temperature without the dead time.
-		self.model = Pot(dt, {**model_params, 'Td': 0})
+		self.model = Pot(dt, {**model_params, 'Td': 0}, theta_amb)
 		# Delayed model: keeps the plant's assumed transport delay, so it
 		# can be compared like-for-like against the real (delayed) measurement.
-		self.model_delay = Pot(dt, model_params)
+		self.model_delay = Pot(dt, model_params, theta_amb)
 
 		self.theta_ist_plant = 0
 		self.theta_ist_model = 0
diff --git a/config.json.sim b/config.json.sim
index 6148917..563b6e3 100755
--- a/config.json.sim
+++ b/config.json.sim
@@ -1,4 +1,5 @@
 {
+	"ambient_temperature": 20,
 	"Controller" : {
 	"dt": 0.1,
 	"sim_warp_factor": 10.0,
diff --git a/config.json.templ b/config.json.templ
index c0a323c..2c581a5 100644
--- a/config.json.templ
+++ b/config.json.templ
@@ -1,4 +1,5 @@
 {
+	"ambient_temperature": 20,
 	"Controller" : {
 	"dt": 1,
 	"sim_warp_factor": 10.0,
diff --git a/scripts/demos/pid/demo_temp_controller.py b/scripts/demos/pid/demo_temp_controller.py
index 9e0b8a1..9b6e765 100644
--- a/scripts/demos/pid/demo_temp_controller.py
+++ b/scripts/demos/pid/demo_temp_controller.py
@@ -31,13 +31,14 @@ if __name__ == '__main__':
 	}
 
 	dt = 1.0
+	theta_amb = 20
 	k_noise = 0.001
 
 	temp_ist = 0
 	temp_soll = 20
 	heatrate_soll = 1.25
 	ctrl = TempController(dt, ctrl_params)
-	plant = Pot(dt, plant_params)
+	plant = Pot(dt, plant_params, theta_amb)
 	_y = np.empty(0)
 	_fb = np.empty(0)
 	_t = np.empty(0)
diff --git a/scripts/demos/pid/demo_temp_controller_smith.py b/scripts/demos/pid/demo_temp_controller_smith.py
index 31e7027..0723ae7 100644
--- a/scripts/demos/pid/demo_temp_controller_smith.py
+++ b/scripts/demos/pid/demo_temp_controller_smith.py
@@ -31,13 +31,14 @@ if __name__ == '__main__':
 	}
 
 	dt = 1.0
+	theta_amb = 20
 	k_noise = 0.001
 
 	temp_ist = 0
 	temp_soll = 20
 	heatrate_soll = 1.25
-	ctrl = TempController(dt, ctrl_params, plant_params)
-	plant = Pot(dt, plant_params)
+	ctrl = TempController(dt, ctrl_params, plant_params, theta_amb)
+	plant = Pot(dt, plant_params, theta_amb)
 	_y = np.empty(0)
 	_fb = np.empty(0)
 	_t = np.empty(0)
diff --git a/scripts/demos/plant/demo_pot.py b/scripts/demos/plant/demo_pot.py
index 181d5be..bf06a06 100644
--- a/scripts/demos/plant/demo_pot.py
+++ b/scripts/demos/plant/demo_pot.py
@@ -5,6 +5,7 @@ from components.plant.pot import Pot
 
 if __name__ == '__main__':
 	dt = 1.0
+	theta_amb = 20
 	power_on = 3500
 	steps_heat = 4000
 	steps_cool = 40000
@@ -18,7 +19,7 @@ if __name__ == '__main__':
 		"gain"		: 1.0
 	}
 
-	pot = Pot(dt, pot_params)
+	pot = Pot(dt, pot_params, theta_amb)
 
 	_t = np.empty(0)
 	_temp = np.empty(0)