Understanding HVAC mode and set point constraints

Learn about specific requirements and constraints for setting HVAC modes and set points on thermostats.

Some models of thermostats have specific requirements and constraints when it comes to setting HVAC modes and set point temperatures. The requirements can be fetched by making a Get Device or List Devices request. 
Sample set of thermostat HVAC mode and set point requirements:
{
  "thermostat": {
    "device_id": "00000000-0000-0000-0000-000000000000",
    "properties": {
      "available_hvac_mode_settings": [
        "off",
        "cool",
        "heat",
        "heat_cool"
      ],
      "can_enable_automatic_cooling": true,
      "can_enable_automatic_heating": true,
      "max_cooling_set_point_celsius": 33.333333333333336,
      "max_heating_set_point_celsius": 26.11111111111111,
      "min_cooling_set_point_celsius": 18.333333333333336,
      "min_heating_set_point_celsius": 7.222222222222222,
      "min_heating_cooling_delta_celsius": 2.7777777777777777,
      "min_heating_set_point_fahrenheit": 45,
      "max_heating_set_point_fahrenheit": 79,
      "min_cooling_set_point_fahrenheit": 65,
      "max_cooling_set_point_fahrenheit": 92,
      "min_heating_cooling_delta_fahrenheit": 5,
      ...
    },
    ...
  },
  ...
}
​
Available HVAC Mode Settings
This property is denoted as available_hvac_mode_settings and includes an array of available HVAC modes. For example, if the array contains ["heat", "off"], it means the thermostat can only be set to either heat or off  modes. The availability of heating or cooling options depends on the connected systems; if the thermostat isn't connected to a specific system, those options may be absent. For an explanation of each mode, read the "What are HVAC modes?" guide.
Example Payload:
"available_hvac_mode_settings": [
  "off",
  "cool",
  "heat",
  "heat_cool"
 ]
Can enable heating / cooling
The settings can_enable_automatic_cooling and can_enable_automatic_heating indicate whether the thermostat supports cooling or heating modes respectively. If can_enable_automatic_cooling is true, it means the thermostat supports cooling. Similarly, if can_enable_automatic_heating is true, the thermostat supports heating. When both are true, the thermostat supports heat-cool mode (also known as "auto"). The availability of heating or cooling options depends on the connected systems; if the thermostat isn't connected to a specific system, those options may be absent. For an explanation of each mode, read the "What are HVAC modes?" guide.
Example Payload:
"can_enable_automatic_cooling": true,
"can_enable_automatic_heating": true
Set point temperature range
The thermostat settings have restrictions on the range of set points temperatures users can choose for both cooling and heating. For cooling, the permissible temperature range is indicated in the min_cooling_set_point_* and max_cooling_set_point_* properties. For heating, the permissible temperature range is indicated in the min_heating_set_point_* and max_heating_set_point_* properties. These properties are available in both Celsius and Fahrenheit, as indicated by the suffix. Users should refer to these parameters to ensure their selected set points fall within the thermostat's defined operational limits.
Example Payload:
"max_cooling_set_point_celsius": 33.333333333333336,
"min_cooling_set_point_celsius": 18.333333333333336,
"max_heating_set_point_celsius": 26.11111111111111,
"min_heating_set_point_celsius": 7.222222222222222,
"min_cooling_set_point_fahrenheit": 65,
"max_cooling_set_point_fahrenheit": 92,
"min_heating_set_point_fahrenheit": 45,
"max_heating_set_point_fahrenheit": 79
Minimum heating cooling delta temperature
The properties min_heating_cooling_delta_celsius and min_heating_cooling_delta_fahrenheit denote the minimum temperature difference, or delta, between the cooling and heating set points when in Auto mode. The cooling set point must always be set higher than the heating one by at least the specified delta. This setting helps prevent the thermostat from rapidly switching between heating and cooling modes, thereby avoiding short cycling.
Example Payload:
"min_heating_cooling_delta_celsius": 2.7777777777777777,
"min_heating_cooling_delta_fahrenheit": 5

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