ESPHome Dew Point Sensor Component

A custom ESPHome component that calculates dew point from existing temperature and humidity sensors using the Magnus formula.

Features

• 🌡️ Accurate dew point calculation using the Magnus formula
• ⚡ Real-time updates when temperature or humidity changes
• 📊 Integrated as a native ESPHome sensor
• 🔧 Simple YAML configuration
• 🎯 Low memory footprint
• 📈 Proper logging and debugging support

Installation

Method 1: Manual Installation

1. Create a dew_point folder in your ESPHome custom_components directory
2. Copy dew_point.h and __init__.py to that folder

Your structure should look like:

config/
└── esphome/
    └── custom_components/
        └── dew_point/
            ├── __init__.py
            └── dew_point.h

Method 2: External Components (Recommended)

Once published to GitHub, you can use:

external_components:
  - source: github://iret33/esphome-dew-point
    components: [ dew_point ]

Configuration

Basic Configuration

sensor:
  # Your existing temperature sensor
  - platform: dht
    pin: GPIO5
    temperature:
      id: room_temperature
      name: "Room Temperature"
    humidity:
      id: room_humidity
      name: "Room Humidity"
    update_interval: 60s

  # Dew point calculation
  - platform: dew_point
    name: "Room Dew Point"
    temperature: room_temperature
    humidity: room_humidity

Advanced Configuration

sensor:
  # BME280 sensor example
  - platform: bme280
    temperature:
      id: outdoor_temp
      name: "Outdoor Temperature"
    humidity:
      id: outdoor_humidity
      name: "Outdoor Humidity"
    pressure:
      name: "Outdoor Pressure"
    address: 0x76
    update_interval: 30s

  # Multiple dew point sensors
  - platform: dht
    pin: GPIO4
    temperature:
      id: indoor_temp
      name: "Indoor Temperature"
    humidity:
      id: indoor_humidity
      name: "Indoor Humidity"

  # Outdoor dew point
  - platform: dew_point
    name: "Outdoor Dew Point"
    id: outdoor_dew_point
    temperature: outdoor_temp
    humidity: outdoor_humidity
    accuracy_decimals: 1
    filters:
      - sliding_window_moving_average:
          window_size: 5
          send_every: 1

  # Indoor dew point
  - platform: dew_point
    name: "Indoor Dew Point"
    id: indoor_dew_point
    temperature: indoor_temp
    humidity: indoor_humidity

Complete Device Example

esphome:
  name: weather-station
  platform: ESP8266
  board: d1_mini

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

logger:
  level: DEBUG

api:
  encryption:
    key: !secret api_encryption_key

ota:
  password: !secret ota_password

sensor:
  # Temperature and Humidity sensor
  - platform: dht22
    pin: GPIO5
    temperature:
      id: temp_sensor
      name: "DHT22 Temperature"
      filters:
        - offset: -0.5  # Calibration offset
    humidity:
      id: humidity_sensor
      name: "DHT22 Humidity"
    update_interval: 60s

  # Dew Point calculation
  - platform: dew_point
    name: "DHT22 Dew Point"
    temperature: temp_sensor
    humidity: humidity_sensor
    icon: "mdi:water-thermometer"

  # WiFi Signal Strength
  - platform: wifi_signal
    name: "Weather Station WiFi Signal"
    update_interval: 60s

Configuration Variables

• temperature (Required, ID): The ID of the temperature sensor (must be in Celsius)
• humidity (Required, ID): The ID of the humidity sensor (must be in percentage 0-100)
• name (Required, string): The name of the dew point sensor
• id (Optional, ID): Manually specify the ID for code generation
• accuracy_decimals (Optional, int): Decimal places for the sensor value. Defaults to 1
• filters (Optional): Standard ESPHome sensor filters
• icon (Optional, string): Custom icon. Defaults to temperature icon
• unit_of_measurement (Optional, string): Unit symbol. Defaults to "°C"

How It Works

The component uses the Magnus formula to calculate dew point:

Td = (b × α) / (a - α)

where:
α = ln(RH/100) + (a × T) / (b + T)
a = 17.27
b = 237.7 °C
T = temperature in °C
RH = relative humidity in %

This formula provides accuracy within ±0.4°C for:

• Temperature range: -40°C to 50°C
• Humidity range: 1% to 100%

Use Cases

HVAC Control

# Prevent condensation
binary_sensor:
  - platform: template
    name: "Condensation Risk"
    lambda: |-
      float dew_point = id(outdoor_dew_point).state;
      float wall_temp = id(wall_temperature).state;
      return (wall_temp < dew_point + 2.0);

Climate Comfort Monitoring

# Comfort level indicator
text_sensor:
  - platform: template
    name: "Comfort Level"
    lambda: |-
      float dew_point = id(indoor_dew_point).state;
      if (dew_point < 10) return {"Dry"};
      else if (dew_point < 13) return {"Comfortable"};
      else if (dew_point < 16) return {"Slightly Humid"};
      else if (dew_point < 18) return {"Humid"};
      else if (dew_point < 21) return {"Very Humid"};
      else return {"Oppressive"};

Mold Prevention

# Mold risk detection
binary_sensor:
  - platform: template
    name: "Mold Risk"
    lambda: |-
      float dew_point = id(basement_dew_point).state;
      return (dew_point > 15.0);  # High mold risk above 15°C dew point

Automation Example

# Turn on dehumidifier when dew point is too high
switch:
  - platform: gpio
    pin: GPIO12
    id: dehumidifier
    name: "Dehumidifier"

automation:
  - platform: numeric_state
    entity_id: sensor.basement_dew_point
    above: 16.0
    then:
      - switch.turn_on: dehumidifier
  - platform: numeric_state
    entity_id: sensor.basement_dew_point
    below: 13.0
    then:
      - switch.turn_off: dehumidifier

Troubleshooting

Sensor shows NaN or no value

Cause: Temperature or humidity sensor not providing valid data

Solution:

• Check that source sensors have valid IDs
• Verify sensors are updating and providing numeric values
• Check ESPHome logs for warnings

Dew point seems incorrect

Cause: Temperature not in Celsius or humidity not in percentage

Solution:

• Ensure temperature sensor outputs Celsius (not Fahrenheit)
• Verify humidity is 0-100% (not 0.0-1.0)
• Check for sensor calibration issues

Component not found

Cause: Component not in correct location

Solution:

• Verify custom_components/dew_point/ exists
• Check both __init__.py and dew_point.h are present
• Restart ESPHome dashboard

High CPU usage

Cause: Too frequent updates

Solution:

• Increase update_interval on source sensors
• Add filters like throttle or delta

Debugging

Enable debug logging:

logger:
  level: DEBUG
  logs:
    dew_point: DEBUG

This will show:

• Calculated dew point values
• Temperature and humidity inputs
• Any warnings or errors

Performance

• Memory: ~100 bytes RAM
• CPU: Minimal (only calculates on sensor updates)
• Accuracy: ±0.4°C (within valid range)
• Update latency: Instant (triggered by source sensor)

Comparison with Other Methods

vs Template Sensor

• ✅ Faster (no YAML parsing)
• ✅ More efficient (compiled C++)
• ✅ Better error handling
• ✅ Native logging

vs Home Assistant Template

• ✅ Calculated on ESP device
• ✅ No network dependency
• ✅ Works even if HA is down
• ✅ Reduces HA load

Related Projects

Home Assistant Integration

If you prefer to calculate dew point in Home Assistant instead of on the ESP device, check out the companion project:

Dew Point Calculator for Home Assistant - A Home Assistant custom integration with UI-based configuration.

Which Should You Use?

Feature	ESPHome Component	Home Assistant Integration
Calculation Location	On ESP device	In Home Assistant
Configuration	YAML	UI-based
Works offline	Yes	Requires HA running
Network dependency	None	Requires network
Resource usage	~100 bytes on ESP	Uses HA resources
Best for	Edge computing, standalone devices	Centralized setup, non-ESPHome sensors
Sensor sources	ESPHome sensors only	Any HA sensor

Choose ESPHome Component when:

• You want calculations done locally on the device
• You need the dew point even when Home Assistant is down
• You're building a standalone weather station
• You want to reduce Home Assistant load

Choose Home Assistant Integration when:

• Your sensors aren't ESPHome devices (Zigbee, Z-Wave, etc.)
• You prefer UI-based configuration
• You want centralized management of all dew point calculations

Contributing

Contributions are welcome! Please:

• Follow ESPHome coding standards
• Test thoroughly before submitting
• Update documentation for new features
• Add examples for new use cases

License

MIT License - See LICENSE file

References

• Magnus Formula
• ESPHome Custom Components
• ESPHome Sensor Documentation

Support

• GitHub Issues: Report bugs or request features
• ESPHome Discord: Get help from the community
• Home Assistant Forum: Discuss use cases

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Made with ❤️ for the ESPHome community