Thermostat started heating

The Thermostat started heating 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 heating. This trigger monitors the hvac_action attribute rather than the HVAC mode. A thermostat can be set to Heat mode but still be idle if the current temperature already meets the target. The trigger only fires when the thermostat actually starts producing heat.

Use this trigger to react to the start of active heating, for example to turn on a fan to distribute warm air or to close window coverings to retain heat.

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 heating 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 heating.
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 heating 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 heating is referred to as climate.started_heating. A basic example looks like this:

trigger: climate.started_heating
target:
  entity_id: climate.living_room

This fires every time climate.living_room begins actively heating.

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 heat, not just set to a heating mode.
• This trigger fires when hvac_action changes to Heating.
• Use this trigger to react to actual heating activity rather than just the device being set to a heating 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 heating

When the first thermostat in the living room area starts heating and continues heating for at least 2 minutes, close all blinds to help retain heat and improve efficiency. The delay prevents the blinds from closing during brief heating cycles, and triggering on the first thermostat avoids multiple blind closures.

• Trigger: Thermostat started heating
  • Target: Living room area
  • Trigger when: First
  • For at least: 2 minutes
• Action: Close cover

alias: "Close blinds when heating"
triggers:
  - trigger: climate.started_heating
    target:
      area_id: living_room
    options:
      behavior: first
      for: "00:02:00"
actions:
  - action: cover.close_cover
    target:
      entity_id: cover.living_room_blinds

Automation: turn on fans when all thermostats are heating

When all thermostats in the bedroom area start heating, turn on ceiling fans on low speed to help distribute the warm air throughout the rooms. Waiting for all thermostats ensures the entire area is being heated before activating air circulation.

• Trigger: Thermostat started heating
  • Target: Bedroom area
  • Trigger when: All
• Action: Turn on fan

alias: "Run fans when all thermostats heating"
triggers:
  - trigger: climate.started_heating
    target:
      area_id: bedroom
    options:
      behavior: last
actions:
  - action: fan.turn_on
    target:
      entity_id: fan.bedroom_ceiling
    data:
      percentage: 30

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 cooling: Triggers after one or more thermostats start cooling.

• 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.