Thermostat started cooling

The Thermostat started cooling trigger fires after a thermostat entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more] begins actively cooling. This trigger monitors the hvac_action attribute rather than the HVAC mode. A thermostat can be set to Cool mode but still be idle if the current temperature already meets the target. The trigger only fires when the thermostat actually starts producing cool air.

Use this trigger to react to the start of active cooling, for example to turn on a fan to distribute cool air or to close window coverings to block out heat.

When you target more than one thermostat, the Trigger when option controls when it fires. You can have it fire the first time any targeted thermostat starts cooling, only after all targeted thermostats have started cooling, or every single time any of them start cooling.

Using this trigger from the user interface

If you prefer building automations visually, Home Assistant walks you through this trigger step by step. You pick what to watch, tweak a few options, and save. No YAML knowledge required.

To use Thermostat started cooling in an automation:

1. Go to Settings > Automations & scenes.
2. Open an existing automation, or select Create automation > Create new automation.
3. In the When section, select Add trigger.
4. Select what you want to monitor. Under By target (see Targets), pick the area your thermostat is in (like your bedroom or living room). You can also select a device, a specific entity, or a label.
5. From the triggers shown for that target, select Thermostat started cooling.
6. Under Trigger when (see Behavior), pick Each, First, or All to control how the trigger behaves when multiple thermostats are targeted.
7. Under For at least, set how long the thermostat must stay in the cooling state before the trigger fires. Leave it at zero to fire immediately.
8. Select Save.

Options in the UI

Using this trigger in YAML

If you work directly in YAML, or you want to know exactly what Home Assistant does under the hood, this section has the technical reference. It lists the field names you use in YAML, their types, and which ones are required.

In YAML, Thermostat started cooling is referred to as climate.started_cooling. A basic example looks like this:

trigger: climate.started_cooling
target:
  entity_id: climate.living_room

This fires every time climate.living_room begins actively cooling.

Options in YAML

YAML sometimes provides additional options for more complex use cases that are not available through the UI.

Targets of the trigger

This trigger requires a target. The target is the object that Home Assistant will watch. You can select a single entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more], a device, an area, a floor, or a label as a target, and Home Assistant will watch every matching climate entity behind that target.

• Entity: one specific climate entity, such as climate.living_room.
• Device: every climate entity that belongs to a device.
• Area: every climate entity in a room or area.
• Floor: every climate entity on a floor.
• Label: every climate entity that shares a label.

You can also select different target types in one trigger. For example, you can add a specific entity and an area as targets in the same trigger to monitor both of them at once.

Behavior with multiple targets

When you target more than one entity (or select an area, floor, or label that contains several), the Trigger when option controls how the trigger responds:

• Each (any in YAML, default): the trigger fires every time any one of the targeted entities transitions. For example, if you monitor three motion sensors in the living room and someone walks past sensor 1, the automation fires. When they walk past sensor 2 a moment later, it fires again. Every individual event counts.
• First (first in YAML): the trigger fires only on the first transition in the targeted group, then waits until all targeted entities have reset before it fires again. For example, if you monitor the same three motion sensors, the automation fires when the first one picks up movement (someone entered the room). The other two firing afterward are ignored, so you get one notification per “someone walked in” event instead of three.
• All (last in YAML): the trigger fires only after the last targeted entity in the group has fired, meaning all of them are now in the expected state. For example, if you monitor the lights in the living room, bedroom, and hallway, the automation fires only once all three have turned off. This is useful for scenarios like “start the robot vacuum only after every light on the floor is off,” so you know the room is truly empty.

Good to know

• The trigger monitors the hvac_action attribute, not the HVAC mode. The climate entity must be actively producing cool air, not just set to a cooling mode.
• This trigger fires when hvac_action changes to Cooling.
• Use this trigger to react to actual cooling activity rather than just the device being set to a cooling mode.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, create a new automation, and add this trigger. Save the automation, then change the state of the targeted entity to watch the trigger fire on your actual entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this trigger fires in automations and scripts. Copy any example and adapt it to your setup.

Automation: close blinds when first thermostat starts cooling

When the first thermostat in the living room area starts cooling and continues cooling for at least 1 minute, close all blinds to block out sunlight and help the air conditioning work more efficiently. The delay avoids closing blinds during brief cooling cycles, and firing on the first thermostat prevents redundant blind closures.

• Trigger: Thermostat started cooling
  • Target: Living room area
  • Trigger when: First
  • For at least: 1 minute
• Action: Close cover

alias: "Close blinds when cooling"
triggers:
  - trigger: climate.started_cooling
    target:
      area_id: living_room
    options:
      behavior: first
      for: "00:01:00"
actions:
  - action: cover.close_cover
    target:
      entity_id: cover.living_room_blinds

Automation: turn on fans when all thermostats are cooling

When all thermostats labeled as main climate controls start cooling, turn on ceiling fans to help distribute the cool air throughout the house. This waits until every targeted thermostat is cooling before activating the fans.

• Trigger: Thermostat started cooling
  • Target: Main thermostats (by label)
  • Trigger when: All
• Action: Turn on fan

alias: "Run fans when all thermostats cooling"
triggers:
  - trigger: climate.started_cooling
    target:
      label_id: main_thermostats
    options:
      behavior: last
actions:
  - action: fan.turn_on
    target:
      entity_id: fan.living_room_ceiling
    data:
      percentage: 50

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with the trigger you’re using and what you expected to happen, or share on our subreddit /r/homeassistant.

Related triggers

These triggers work well alongside this one:

• Thermostat started heating: Triggers after one or more thermostats start heating.

• Thermostat started drying: Triggers after one or more thermostats start drying.

• Thermostat mode changed: Triggers after the HVAC mode of one or more climate devices changes.