diff --git a/main.c b/main.c
--- a/main.c
+++ b/main.c
@@ -89,6 +89,7 @@ int main(void)
     uint32_t last_vcp_tx = 0;
     uint32_t last_led = 0;
     uint32_t last_pid = 0;
+    uint32_t last_thermostat = 0;
     int16_t ssr_output = 0; // Duty cycle of ssr, 0 to SSR_PERIOD 
 
     // Main loop
@@ -101,7 +102,7 @@ int main(void)
             last_led = HAL_GetTick();
         }
 
-        if((HAL_GetTick() - last_pid > PID_PERIOD))
+        if(set.val.control_mode == MODE_PID && (HAL_GetTick() - last_pid > PID_PERIOD))
         {
 
             #ifdef MAX31865_RTD_SENSOR
@@ -115,6 +116,10 @@ int main(void)
             {
                 // Get ssr output for next time
                 int16_t power_percent = pid_update(&set, &status, &pid_state);
+
+                if(set.val.plant_type == PLANT_HEATER)
+                    power_percent *= -1;
+
                 //power-percent is 0-1000?
                 ssr_output = power_percent; //(((uint32_t)SSR_PERIOD * (uint32_t)10 * (uint32_t)100) * power_percent) / (uint32_t)1000000;
 
@@ -134,20 +139,19 @@ int main(void)
         }
 
         // Kill SSR once the desired on-time has elapsed
-        if(HAL_GetTick() - last_ssr_on > ssr_output || ssr_output <= 0)
+        if(set.val.control_mode == MODE_PID && (HAL_GetTick() - last_ssr_on > ssr_output || ssr_output <= 0))
         {
             HAL_GPIO_WritePin(SSR_PIN, 0);
             HAL_GPIO_WritePin(LED_POWER, 0);
         }
 
+
         // Every 200ms, set the SSR on unless output is 0
-        if(HAL_GetTick() - last_ssr_on > SSR_PERIOD)
+        if(set.val.control_mode == MODE_PID && HAL_GetTick() - last_ssr_on > SSR_PERIOD)
         {
-
-            // Only support heating (ssr_output > 0) right now
+            // Heat or cool, if we need to 
             if(ssr_output > 0) 
             {
-
                 HAL_GPIO_WritePin(SSR_PIN, 1);
                 HAL_GPIO_WritePin(LED_POWER, 1);
                 last_ssr_on = HAL_GetTick();
@@ -160,6 +164,55 @@ int main(void)
             
         }
         
+
+        // Thermostatic control
+        if(set.val.control_mode == MODE_THERMOSTAT && HAL_GetTick() - last_thermostat > SSR_PERIOD)
+        {
+
+            #ifdef MAX31865_RTD_SENSOR
+            max31865_readtemp(spi_get(), &set, &status);
+			#else
+			max31855_readtemp(spi_get(), &set, &status); // Read MAX31855
+			#endif
+
+            // TODO: Migrate this FxP conversion to the readtemp code or similar
+            int8_t temp_frac = status.temp_frac > 9 ? status.temp_frac / 10 : status.temp_frac;
+            temp_frac = status.temp > 0 ? temp_frac : temp_frac * -1;
+            int32_t temp = (status.temp * 10) + temp_frac;
+
+            uint8_t plant_on = 0;
+
+            // EMZ FIXME: This could be way simpler
+            if(set.val.plant_type == PLANT_HEATER && status.setpoint * 10 < temp)
+                plant_on = 1;
+            else if(set.val.plant_type == PLANT_COOLER && status.setpoint * 10 > temp)
+                plant_on = 1;
+
+            // EMZ: TODO: Refactor to output_enabled or something
+            if(status.pid_enabled && plant_on)
+            {
+                // EMZ TODO: functionalize this
+            	// put ssr output on display
+                ssd1306_drawstring("      ", 0, 90); //fixme: this is bad, but I can't get the old digits to clear otherwise
+                char tempstr[6];
+                itoa(ssr_output, tempstr, 10);
+                ssd1306_drawstring(tempstr, 0, 90);
+
+
+
+                HAL_GPIO_WritePin(SSR_PIN, 1);
+                HAL_GPIO_WritePin(LED_POWER, 1);
+            }
+            else
+            {
+                HAL_GPIO_WritePin(SSR_PIN, 0);
+                HAL_GPIO_WritePin(LED_POWER, 0);
+            }
+            
+            last_thermostat = HAL_GetTick();
+        }
+
+
         // Transmit temperature over USB-CDC on a regular basis
         if(HAL_GetTick() - last_vcp_tx > VCP_TX_FREQ)
         {