> ## Documentation Index > Fetch the complete documentation index at: https://docs.ariscomfort.com/llms.txt > Use this file to discover all available pages before exploring further. # Get FCU status > Returns detailed telemetry for a specific fan coil unit. ## OpenAPI ````yaml get /api/fcus/{fcuId} openapi: 3.1.0 info: title: Aris API version: 1.0.0 description: > REST API for controlling Aris home comfort systems. Aris is an air-to-water heat pump system that heats, cools, and provides hot water for homes. The Aris Brain is the central controller, managing zones, fan-coil units (FCUs), heat pumps, domestic hot water (DHW), and thermal energy storage (TES). ## Base URL The Aris Brain runs on your local network. Find your Brain's address via: - mDNS: `http://aris.local` (if your network supports mDNS) - Router admin panel: Look for a device named "aris-brain" ## Authentication Most API endpoints require authentication via Bearer token. Create an API token in the Aris web UI under **Settings → API Tokens**. Include the token in the `Authorization` header: ``` Authorization: Bearer your-api-token ``` ## Real-time Updates For real-time updates, connect to the WebSocket at `ws://aris.local?token=YOUR_API_TOKEN`. The WebSocket broadcasts zone state changes, system events, and device telemetry. servers: - url: http://aris.local description: Local network (mDNS) - url: http://{brainIp} description: Local network (IP address) variables: brainIp: default: 192.168.1.100 description: Your Aris Brain's IP address security: [] tags: - name: Health description: Health check and readiness endpoints - name: System description: System-wide state and mode control - name: Zones description: Zone management, setpoints, and temperature control - name: DHW description: Domestic Hot Water tank status and history - name: TES description: Thermal Energy Storage tank status - name: HCU description: Hydronic Control Unit status - name: Heat Pumps description: Heat pump telemetry and diagnostics - name: FCUs description: Fan Coil Unit telemetry and status - name: Weather description: Weather data and forecasts - name: Events description: System event log and audit trail - name: Metrics description: VictoriaMetrics time-series data proxy - name: Prometheus description: Prometheus-compatible API for Grafana - name: Tokens description: API token management - name: Config description: System configuration (read-only) - name: Firmware description: FCU firmware OTA updates paths: /api/fcus/{fcuId}: get: tags: - FCUs summary: Get FCU status description: Returns detailed telemetry for a specific fan coil unit. operationId: getFCU parameters: - name: fcuId in: path required: true schema: type: string example: fcu_01a9 responses: '200': description: FCU status content: application/json: schema: $ref: '#/components/schemas/FCU' '401': $ref: '#/components/responses/Unauthorized' '404': description: FCU not found content: application/json: schema: $ref: '#/components/schemas/Error' security: - bearerAuth: [] components: schemas: FCU: type: object description: > A Fan Coil Unit (FCU) is an active, powered terminal that delivers heating, cooling, and (where supported) dehumidification to a zone. FCUs use forced convection — a fan moving air across a water coil — to condition the room. FCUs receive airflow and mode commands from the Aris Brain and apply local safety logic for comfort and protection (cold-blow prevention, condensation protection, fan-ramp behavior). The reported mode may differ from the commanded mode due to these local safety adjustments. properties: fcuId: type: string description: Unique identifier for the FCU. example: fcu_01a9 friendlyName: type: string description: Human-readable name for the FCU (e.g., "Living Room FCU"). example: Living Room FCU mode: type: string enum: - heat - cool - idle - inhibit description: > Resolved operating state of the FCU after applying local safety and protection logic. This may differ from the commanded mode due to cold-blow prevention, condensation protection, or other safety measures. - `heat`: FCU is actively heating - `cool`: FCU is actively cooling - `idle`: FCU is not actively conditioning - `inhibit`: FCU operation is inhibited by local safety logic example: heat fanPercent: type: integer minimum: 0 maximum: 100 description: > Current airflow level expressed as a normalized percentage (0-100%). FCUs with discrete speed steps (e.g., low/medium/high) map those steps into percentage values: Low = 1-33%, Medium = 34-66%, High = 67-100%. example: 60 roomTempC: type: number description: > Local air temperature measured at the FCU (in Celsius). May contribute to zone temperature resolution when multiple sensors are present. example: 22.5 rhPercent: type: number description: >- Local relative humidity measured at the FCU (if equipped with humidity sensor). example: 46 supplyTempC: type: number description: >- Temperature of the water entering the FCU coil (system supply), in Celsius. example: 38.2 returnTempC: type: number description: >- Temperature of the water leaving the FCU coil (system return), in Celsius. example: 33.7 activeFaults: type: array items: type: string description: > List of currently active fault codes for this FCU (e.g., ["F010", "F011"]). F010 indicates an airflow fault. Empty array means no active faults. example: [] filterLastChangedTs: type: string format: date-time description: > Timestamp of the most recent filter replacement (ISO 8601). Used for maintenance reminders and tracking filter life. example: '2025-03-12T09:14:00Z' Error: type: object properties: error: type: string description: Error type message: type: string description: Human-readable error message hint: type: string description: Suggestion for resolving the error responses: Unauthorized: description: Missing or invalid authentication content: application/json: schema: type: object properties: error: type: string example: Unauthorized message: type: string example: Valid authentication required securitySchemes: bearerAuth: type: http scheme: bearer description: Session token or API token ````