diff --git a/homeassistant/components/thermostat/__init__.py b/homeassistant/components/thermostat/__init__.py
index 8d811c3a5cc..535a98567d8 100644
--- a/homeassistant/components/thermostat/__init__.py
+++ b/homeassistant/components/thermostat/__init__.py
@@ -33,6 +33,7 @@ SERVICE_SET_HVAC_MODE = "set_hvac_mode"
 STATE_HEAT = "heat"
 STATE_COOL = "cool"
 STATE_IDLE = "idle"
+STATE_AUTO = 'auto'
 
 ATTR_CURRENT_TEMPERATURE = "current_temperature"
 ATTR_AWAY_MODE = "away_mode"
diff --git a/homeassistant/components/thermostat/radiotherm.py b/homeassistant/components/thermostat/radiotherm.py
index 963ef1a9a7f..c4031fde940 100644
--- a/homeassistant/components/thermostat/radiotherm.py
+++ b/homeassistant/components/thermostat/radiotherm.py
@@ -9,7 +9,8 @@ import logging
 from urllib.error import URLError
 
 from homeassistant.components.thermostat import (
-    STATE_COOL, STATE_HEAT, STATE_IDLE, ThermostatDevice)
+    STATE_AUTO, STATE_COOL, STATE_HEAT, STATE_IDLE, STATE_OFF,
+    ThermostatDevice)
 from homeassistant.const import CONF_HOST, TEMP_FAHRENHEIT
 
 REQUIREMENTS = ['radiotherm==1.2']
@@ -122,3 +123,14 @@ class RadioThermostat(ThermostatDevice):
         now = datetime.datetime.now()
         self.device.time = {'day': now.weekday(),
                             'hour': now.hour, 'minute': now.minute}
+
+    def set_hvac_mode(self, mode):
+        """Set HVAC mode (auto, cool, heat, off)."""
+        if mode == STATE_OFF:
+            self.device.tmode = 0
+        elif mode == STATE_AUTO:
+            self.device.tmode = 3
+        elif mode == STATE_COOL:
+            self.device.t_cool = self._target_temperature
+        elif mode == STATE_HEAT:
+            self.device.t_heat = self._target_temperature