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 Carbon dioxide value 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 carbon dioxide sensor is in (like your bedroom or office). You can also select 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 level the condition checks against:
   1. Pick whether the reading must be Above, Below, In range, or Outside range of the threshold.
   2. Select Number or Entity:
      • Number: Enter a fixed level directly, for example 1000 for 1000 ppm. For In range or Outside range, enter both a lower and upper bound.
      • Entity: Use a sensor entity or a number helper entity as the threshold:
        • Number helper: You can adjust the threshold value without editing the automation. The sensor reading is compared against the number helper’s current value.
        • Sensor: Its current reading becomes the threshold and updates automatically as the sensor changes.
        • For In range or Outside range, you need two entities: one for the lower bound and one for the upper bound (for example, two separate number helpers).
        • If you don’t have a number helper, you can create one by selecting Create a new number helper.
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. For how an automation is built in YAML, refer to Automations in YAML.

In YAML, put the settings that are specific to this condition under options. Keep target, if the condition uses one, and general settings such as alias and enabled at the top level, next to condition.

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:
    type: above
    value:
      number: 1000
  behavior: any

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

Options in YAML

Targets of the condition

This condition requires a target. The target is the object that Home Assistant will check. You can point the condition 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 will evaluate every matching carbon dioxide sensor behind that target.

• Entity: one specific carbon dioxide sensor, such as sensor.living_room_co2.
• Device: every carbon dioxide sensor that belongs to a device.
• Area: every carbon dioxide sensor in a room or area.
• Floor: every carbon dioxide sensor on a floor.
• Label: every carbon dioxide sensor that shares a label.

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

To learn which entities Home Assistant includes for a device, area, floor, or label, and how it handles several entities, refer to Automation targets.

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 or unknown are skipped. With Any, the condition passes if at least one of the other targeted sensors matches. With All, it passes if all the other targeted sensors match. If all targeted sensors are unavailable or unknown, All passes and Any fails.
• Outdoor CO2 levels are typically around 420 ppm. Indoor levels above 1000 ppm often suggest the room needs better ventilation.
• The threshold is in ppm. A sensor that reports CO2 in another unit never matches. If you use an entity as the threshold, it must also report ppm.

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. In the visual editor, select the UI options listed in the example or paste the YAML code.

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 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: Carbon dioxide value
  • Target: Bedroom CO2 sensor
  • Threshold type: Above 1000 ppm
• Action: Turn on fan
  • Target: Bedroom ventilation

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:
        type: above
        value:
          number: 1000
actions:
  - action: fan.turn_on
    target:
      entity_id: fan.bedroom_ventilation

Still stuck?

To find out why the condition didn’t pass, check it live in the automation editor, and look at the trace of the run. For details, refer to Testing automations. For common problems and their solutions, refer to Troubleshooting automations.

If that doesn’t help, 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

Explore related conditions:

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