Building a Smart Ventilation System with Heat Recovery for Older Homes Using Home Assistant

Introduction

In older homes with natural (gravity-based) ventilation systems, maintaining healthy indoor air quality can be challenging. High humidity, CO₂ levels, and VOCs (volatile organic compounds) can compromise comfort and health. This project transforms an existing system into a smart, automated ventilation system integrated with Home Assistant, ensuring balanced pressure, efficient heat recovery, and adaptive airflow based on real-time sensor data.

How the System Works

Sensors: Place air quality sensors in multiple rooms to measure:
- CO₂ levels (e.g., <1000 ppm ideal)
- VOC concentrations
- Indoor pressure relative to outdoor pressure
Balanced Ventilation with Motors:
- Separate intake and exhaust air channels, each equipped with fans controlled by motors.
- Both systems are linked to maintain neutral pressure, preventing over- or underpressure.
Heat Recovery: Air ducts are designed with a heat recovery ventilator (HRV), transferring heat from outgoing air to incoming air without mixing the two streams.
Adaptive Automation:
- Ventilation intensity adjusts dynamically based on sensor data.
- Airflow increases when CO₂, VOCs, or humidity exceed safe thresholds.
- When air quality is optimal, ventilation reduces to conserve energy.
Pressure Equalization: By balancing internal and external air pressures, moisture transfer into walls and structures is minimized, protecting the building.

Design and Components

Hardware

Component	Purpose	Estimated Cost
ESP32 / ESP8266	Microcontroller for Home Assistant integration	€10–20
CO₂ Sensors (e.g., MH-Z19B)	Monitor carbon dioxide levels	€20–30 each
VOC Sensors (e.g., CCS811)	Detect air quality (VOCs)	€15–25 each
Pressure Sensors (e.g., BMP280)	Measure indoor/outdoor air pressure	€10–15 each
Duct Fans (Intake/Exhaust)**	Maintain airflow	€80–150 per fan
Heat Recovery Unit	Transfer heat between air streams	€600–1500
Power Supply	Power motors and sensors	€20–50

Total System Estimate: €1000–2000 (depending on house size and components).

Calculating Air Exchange Requirements

To maintain healthy air quality, indoor air should be replaced at a rate of 0.5 air changes per hour (ACH). For a typical home:

House Size: 120 m² (floor area) x 2.5 m (ceiling height) = 300 m³ total volume.
Airflow Requirement: 0.5 ACH×300 m3=150 m3/h0.5 \, \text{ACH} \times 300 \, \text{m}^3 = 150 \, \text{m}^3/\text{h}0.5ACH×300m3=150m3/h

For a 300 m³ home, you need a ventilation capacity of at least 150 m³/h. Select fans and ducts capable of meeting this requirement with some overhead (e.g., 200–250 m³/h).

Home Assistant Configuration

Integrate Sensors

Use ESPHome to connect sensors to Home Assistant. Example YAML for a CO₂ sensor:

yaml
esphome:
  name: ventilation_monitor

sensor:
  - platform: mhz19
    co2:
      name: "Living Room CO2"
    temperature:
      name: "Sensor Temperature"
    update_interval: 60s

Automate Ventilation

Create automations in Home Assistant to adjust fan speeds and maintain air quality:

yaml
alias: "Increase Ventilation When CO2 High"
trigger:
  - platform: numeric_state
    entity_id: sensor.living_room_co2
    above: 1000
action:
  - service: fan.turn_on
    target:
      entity_id: fan.exhaust_fan
  - service: fan.turn_on
    target:
      entity_id: fan.intake_fan

Pressure Equalization

Using outdoor and indoor pressure sensors, adjust fan speeds to balance the air pressure:

yaml
alias: "Pressure Equalization"
trigger:
  - platform: numeric_state
    entity_id: sensor.indoor_pressure
    above: sensor.outdoor_pressure
action:
  - service: fan.set_speed
    target:
      entity_id: fan.exhaust_fan
    data:
      speed: 50
  - service: fan.set_speed
    target:
      entity_id: fan.intake_fan
    data:
      speed: 50

Benefits of the System

Improved Air Quality: CO₂, VOC, and humidity levels remain optimal.
Energy Efficiency: Heat recovery reduces heating costs during winter.
Moisture Management: Neutral pressure prevents moisture from entering structures.
Automation: Home Assistant provides real-time monitoring and control.
Adaptability: The system scales for larger homes or additional sensors.

Conclusion

Transforming an old home’s natural ventilation system into a smart, automated solution improves air quality, conserves energy, and protects the building structure. Using affordable components and integrating them with Home Assistant, you can achieve precise control over ventilation rates, pressure, and heat recovery. While initial setup costs range from €1000–2000, the long-term benefits in energy savings and health are well worth the investment.