Carbon dioxide value

The Carbon dioxide value condition passes when a carbon dioxide (CO2) sensor’s reading meets a specific level. A stuffy meeting room, a crowded living room on movie night, or a bedroom with the door closed overnight all push CO2 levels higher than you would expect. This condition lets your automation act only when CO2 is genuinely elevated, so the ventilation fan starts when it is truly needed and stays off when the air is fine.

Using this condition from the user interface

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

To use this condition in an automation:

1. Go to Settings > Automations & scenes.
2. Open an existing automation, or select Create automation > Create new automation.
3. In the And if section, select Add condition.
4. Select what you want to check. Under By target (see Targets), pick the area your air quality sensor is in (like your living room or bedroom). You can also select a floor, a device, a specific entity, or a label.
5. From the conditions shown for that target, select Carbon dioxide value.
6. Under Threshold type, set the CO2 level the condition checks against.
7. Under Condition passes if (see Behavior), pick Any or All.
8. Select Save.

Options in the UI

Using this condition 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, refer to this condition as air_quality.is_co2_value. A basic example looks like this:

condition: air_quality.is_co2_value
target:
  entity_id: sensor.office_co2
options:
  threshold: 1000
  behavior: any

This passes when the office CO2 sensor reads at or above 1000 ppm.

Options in YAML

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

Targets

This condition supports targets. A target tells Home Assistant what the condition should check. You can point it at 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, and Home Assistant evaluates every matching air_quality entity behind that target.

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

You can also mix target types in one condition. For example, combine a specific entity with an area to check both at once.

Behavior with multiple targets

When you target more than one entity (or select an area, floor, or label that contains several), the Condition passes if option controls how the results combine:

• Any (default): the condition passes if at least one of the targeted entities matches. For example, if you check three smoke sensors and only one of them detects smoke, the condition still passes. This is useful for questions like “is there smoke anywhere in the house?”
• All: the condition passes only when every targeted entity matches. For example, if you check the same three smoke sensors, the condition passes only once all three report cleared. This is useful for “is the entire house safe now?” checks, so your automation does not send an all-clear while one room still has a reading.

Good to know

• Sensors that are unavailable (unavailable) or have an unknown state (unknown) are skipped for Any and fail for All.
• Outdoor CO2 levels are typically around 420 ppm. Indoor levels above 1000 ppm often suggest the room needs better ventilation.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, open an automation, and add this condition. Trigger the automation with and without the condition met, and watch whether it continues or stops.

More examples

Real scenarios where this condition gates an automation. Copy any example and adapt it to your setup.

Automation: turn on ventilation at bedtime only if CO2 is elevated

After you spend an evening in the living room with the doors closed, CO2 levels are sometimes higher than you would expect by the time you head to bed. This automation triggers at your usual bedtime and checks the bedroom CO2 reading. If the level is at or above 1000 ppm, the ventilation fan turns on so you sleep with fresh air. On evenings when the room already has good airflow, the fan stays off.

• Trigger: Time: 22:30
• Condition: Air Quality: Carbon dioxide value
• Target: Bedroom CO2 sensor
• Threshold type: 1000
• Condition passes if: Any
• Action: Fan: Turn on

alias: "Bedtime ventilation if CO2 is high"
triggers:
  - trigger: time
    at: "22:30:00"
conditions:
  - condition: air_quality.is_co2_value
    target:
      entity_id: sensor.bedroom_co2
    options:
      threshold: 1000
      behavior: any
actions:
  - action: fan.turn_on
    target:
      entity_id: fan.bedroom_ventilation

Still stuck?

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

Related conditions

These conditions work well alongside this one:

• Volatile organic compounds value - Tests the volatile organic compounds level of one or more entities.