Dew Point Calculator for Home Assistant

A Home Assistant custom integration that calculates dew point from existing temperature and humidity sensors.

Features

• 🌡️ Calculate dew point from any temperature and humidity sensor
• 🎯 Easy configuration through the UI
• ⚡ Real-time updates when sensor values change
• 📊 Uses the accurate Magnus formula for calculation
• 🔄 Multiple dew point sensors can be created

Installation

HACS (Recommended)

1. Open HACS in Home Assistant
2. Go to "Integrations"
3. Click the three dots in the top right corner
4. Select "Custom repositories"
5. Add this repository URL: https://github.com/iret33/ha-dew-point-calculator
6. Select category: "Integration"
7. Click "Add"
8. Find "Dew Point Calculator" in the integration list
9. Click "Download"
10. Restart Home Assistant

Manual Installation

1. Download the custom_components/dew_point_calculator folder from this repository
2. Copy it to your Home Assistant's custom_components directory
   • If the custom_components directory doesn't exist, create it in your config folder
3. Restart Home Assistant

Configuration

1. Go to Settings → Devices & Services
2. Click + Add Integration
3. Search for Dew Point Calculator
4. Select your temperature sensor
5. Select your humidity sensor
6. Give your dew point sensor a name (optional)
7. Click Submit

The dew point sensor will be created and will update automatically whenever the temperature or humidity changes.

How It Works

The integration 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 temperatures between -40°C and 50°C.

Example Use Cases

• HVAC Control: Prevent condensation by monitoring dew point
• Comfort Monitoring: Track indoor air quality
• Greenhouse Management: Optimize growing conditions
• Mold Prevention: Alert when conditions favor mold growth
• Weather Stations: Complete weather data reporting

Troubleshooting

Sensor shows "unavailable"

• Check that both temperature and humidity sensors are working
• Verify the sensors are providing valid numeric values

Dew point seems incorrect

• Ensure your temperature sensor is in Celsius
• Verify humidity sensor reads 0-100%
• Check that sensors are reading from the same location

Related Projects

ESPHome Component

If you're using ESPHome devices and want to calculate dew point directly on the ESP device, check out the companion project:

ESPHome Dew Point Sensor Component - Calculate dew point directly on your ESP8266/ESP32 devices.

Which Should You Use?

Feature	Home Assistant Integration	ESPHome Component
Calculation Location	In Home Assistant	On ESP device
Configuration	UI-based	YAML
Works offline	Requires HA running	Yes
Sensor sources	Any HA sensor	ESPHome sensors only
Best for	Centralized setup, mixed sensors	Edge computing, standalone

Choose Home Assistant Integration when:

• Your sensors aren't ESPHome devices (Zigbee, Z-Wave, WiFi, etc.)
• You prefer UI-based configuration
• You want centralized management of all dew point calculations
• You're using sensors from different protocols/brands

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

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Support

If you encounter any issues or have questions:

• Open an issue on GitHub
• Check the Home Assistant Community Forum

Changelog

Version 1.0.0

• Initial release
• UI-based configuration
• Real-time dew point calculation
• Support for multiple sensors

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Made with ❤️ for the Home Assistant community