ESPHome Zehnder ComfoAir E300/E350/E400

Interact with Zehnder ComfoAir E300/E350/E400 using ESPHome and Home Assistant. This ESPHome component provides interaction with Zehnder ComfoAir E300/E350/E400 heat recovering ventilation units. Sensor states are read using modbus RTU, while the unit is controlled using the analog input. This integration is likely to work with the ComfoAir PRO 200/250/300 series as well, but this remains untested.

Setup

The component uses modbus RTU serial communication over RS485 to interface with the ventilation unit, furthermore the analog input on the C1 connector is used to control the ventilation level. The serial communication is available on the C3 connector. The C3 connector is located at the top right of display. To access it, remove the cover surrounding the display by removing three Torx screws. The pin-out is shown in the image below:

Connector	Description
C1	Analog (0-10 V) control input
C2	Bathroom switch
C3	RS485 serial interface
C4	Malfunction indicator (5V when malfunction is detected)

Hardware

The example hardware is based on a ESP32 and a MAX485 module that converts the RS485 signal to UART.

Since the RS485 connection is half-duplex, it cannot send and receive data at the same time, unlike UART. To overcome this issue, the module uses flow control to determine if it should be sending or receiving data. Two different types of module are available, with and without automatic flow control.

Without automatic flow control	With automatic flow control

Note that the pin-out differs. The module with automatic flow control has input pins labeled TDX and RDX while the module without automatic flow control has pins labeled DI, RO, RE and DE.

Warning

Check the input voltage for the MAX485 module. Most modules support both 3.3 V and 5 V. However, some units (mainly those without flow control) only support 5 V. These units will use 5 V logic levels that might damage your ESP device when used without a level shifter. Alternatively, you can use a MAX3485 module which support 3.3 V logic natively.

Both modules can be used in this project, the only difference being the availability of the module, and the requirement for an additional free pin.

In order to connect the MAX485 module to the nodeMCU the following mapping can be used.

nodeMCU	MAX485	MAX485 (w/o flow control)
GPI01	TDX	DI (Driver Input)
GPI03	RDX	RO (Receiver Output)
GPIO5	-	RE (Receiver Enable)
GPIO5	-	DE (Driver Enable)
3V3	VCC	VCC
GND	GND	GND

Finally, the A+ and B- ports of the MAX485 module should be connected to the A+ and B- ports on the C3 connector using a twisted pair.

Fan control

To control the fan, the analog (0–10 V) input on the C1 connector is used. Since the ESP chip can only provide 3.3 V, the unit's max instelling must be lowered to 3.1 V so the unit interprets 3.3 V as the maximum ventilation level. The setting is located at: menu -> login (pwd 4210) -> analog 0-10V -> max. instelling.

Three options are available for generating the required signal:

• ESP8266: software PWM can generate the required signal.
• ESP32: built-in DAC can be used.
• External DAC (e.g. DFRobot Gravity GP8211S) for true 0–10 V output; required if multiple wired 0–10 V inputs are used (ComfoConnect Splitter).

Filter Replacement Timer

Since the filter status cannot be read directly from the ventilation unit, the component includes a filter replacement timer that tracks operating hours.

Features:

• Operating Hours Tracking: Monitors filter age.
• Configurable Interval: Set custom replacement intervals (30-365 days, default 180 days).
• Smart Alerts: Binary sensor indicates when replacement is due.
• Remaining Time: Shows days until next replacement is needed.
• Auto Reset: Detect when the filters are replaced.

Schematic

The following schematic shows how to connect the hardware.

+---------------+                                    +-------------+
|         12V   |                                    |             |
|   C1    0-10V o------------------------------------o GPIOxx      |
|         GND   o------------------------------------o GND         |
|  [ComfoAir    |                                    |             |
|   E300/E400]  |       +--------------------+       |    [ESP]    |
|         B-    o-------o B-             VCC o-------o 3v3         |
|   C3    A+    o-------o A+             GND o-------o GND         |
|               |       |      [MAX485]      |       |             |
+---------------+       |                 TX o-------o TXD         |
                        |                 RX o-------o RXD         |
                        +--------------------+       +-------------+

Example — minimal configuration

Minimal ESPHome configuration required to use this component. Example files for other boards and setups are available in the examples directory — adjust pins and secrets (Wi‑Fi, API/OTA keys) to match your hardware.

Check your firmware version

Each FW version has a seperate configuration, since the number of available sensors is dependent on the FW version. To check your FW version:

On older FW versions (1.x.x):

Menu -> login (pwd 4210) -> toestel specificatie -> SW

Or on the newer FW models (2.x.x) and (3.x.x):

Menu -> Opties -> SW

Basic configuration (ESP32 example):

substitutions:
  tx_pin: GPIO01
  rx_pin: GPIO03
  update_interval: 15s
  fan_output: fan_output
  # fan_speed_count: "100"  # uncomment this to get a continuous 0-100% slider instead of the default 3 presets

# If your MAX485 module does not have automatic flow control, uncomment and set a flow control pin:
# modbus:
#   flow_control_pin: GPIO16

packages:
  remote_package:
    url: https://github.com/CodedCactus/zehnder-comfoair
    ref: main
    files: [components/zehnder_fw{major}.yaml, # use fw1, fw2 or fw3 depending on your unit
            components/fan.yaml,               # comment out fan.yaml if you don't want fan control
            components/filter.yaml,            # comment out filter.yaml if you don't want filter replacement timer
            components/extra-sensors.yaml]     # comment out extra-sensors.yaml if you don't want extra entities
    refresh: 0s

output:
  - platform: esp32_dac
    pin: GPIO25
    id: fan_output

Notes:

• Verify GPIO pins match your board and wiring.
• If using a MAX485 without automatic flow control, enable the modbus.flow_control_pin entry above.
• Use the examples/ folder as starting points for other configurations and hardware variants.

Registry table

The following data fields have been identified from the holding registers. Currently, all registers are read-only.

Address	Name	Datatype	Unit	Scale	Note
0x065	Device Status	U_WORD	-	-	0: Error; 1:Initializing; 2: Self Test; 3: Waiting for user input; 10: Normal; 20: Standby; 42: Service Mode
0x06E	Firmware version	U_WORD	-	-	20800 = 2.8.0
0x06F	Orientation	U_WORD	-	-	0:Right; 1:Left
0x070	Model	U_WORD	-	-	0:E300 P; 2:E300 RF; 3:E400 RF
0x12C	Outdoor temperature	S_WORD	°C	10
0x12D	Pre-heater temperature	S_WORD	°C	10
0x12F	Supply temperature	S_WORD	°C	10
0x130	Extract temperature	S_WORD	°C	10
0x131	Exhaust temperature	S_WORD	°C	10
0x132	Outdoor humidity	U_WORD	%	10
0x133	Supply humidity	U_WORD	%	10
0x134	Extract humidity	U_WORD	%	10
0x135	Exhaust humidity	U_WORD	%	10
0x136	Exhaust fan duty cycle	U_WORD	%	10
0x137	Supply fan duty cycle	U_WORD	%	10
0x138	Exhaust flow rate	U_WORD	m³/h	1
0x139	Supply flow rate	U_WORD	m³/h	1
0x13A	Exhaust fan speed	U_WORD	RPM	1
0x13B	Supply fan speed	U_WORD	RPM	1
0x13C	Analog (0-10 V) input voltage	U_WORD	V	100	Steering signal (0-10V)
0x13D	RF input voltage	U_WORD	V	100	Steering signal (0-10V)
0x13E	RF input enabled	U_WORD	-	-	0:Off; 1:On
0x13F	Pre-heater status	U_WORD	-	-	0:Off; 1:On
0x140	Supply flow rate setpoint	U_WORD	m³/h	1
0x141	Exhaust flow rate setpoint	U_WORD	m³/h	1	Balance off-set is applied to this setpoint
0x142	Running Mean Outdoor Temperature	S_WORD	°C	10
0x145	Bypass motor active	U_WORD	-	1	0:reset bypass position; 1:end position reached; 2:active
0x146	Bypass setpoint	U_WORD	%	1	0:Closed; 100:Fully open
0x147	Bypass position	U_WORD	%	1	0:Closed; 100:Fully open
0x148	Analog (0-10 V) control setpoint	U_WORD	%	1	0:Low; 50:Medium; 100:High
0x149	RF control setpoint	U_WORD	%	1	0:Low; 50:Medium; 100:High
0x14A	3-way switch control setpoint	U_WORD	%	1	0:Low; 50:Medium; 100:High
0x14B	Bathroom switch control setpoint	U_WORD	%	1	0:Low; 50:Medium; 100:High
0x14E	Nr. of defrost cycles last 24 h	U_WORD	-	1
0x152	Pre-heater present*	U_WORD	-	-	0:Absent; 1:Present
0x158	Heat exchanger type	U_WORD	-	-	0:HRV; 1:ERV
0x159	Comfort Humidity control	U_WORD	-	-	0:Disabled; 1:Enabled
0x151	Fireplace mode*	U_WORD	-	-	0:Off; 1:On

*Only available on later firmware versions (confirmed on 2.8.0)

Additional sensors

extra-sensors.yaml provides additional entities which might be useful. They are calculated on the ESPHome device. Have a look at the Thermal Comfort integration if you prefer to have some of these values calculated in home assistant.

Name	Unit	Note
Outdoor dew point	°C	The temperature to which air must be cooled to form dew (100% humidity)
Supply dew point	°C	Dew point is closely related to the perceived dryness of air
Extract dew point	°C
Exhaust dew point	°C
Outdoor absolute humidity	g/m³	The amount of water vapor (g) present in 1m³ the air
Supply absolute humidity	g/m³
Extract absolute humidity	g/m³
Exhaust absolute humidity	g/m³
Outdoor enthalpy	kJ/h	The amount of energy (kJ) transported by the air every hour
Supply enthalpy	kJ/h	Enthalpy is for air what energy is for electricity
Extract enthalpy	kJ/h
Exhaust enthalpy	kJ/h
Delta temperature	°C	The difference between supply temperature and extract temperature
Delta moisture	g/m³	The difference between outdoor humidity and exhaust humidity
Delta energy	kJ/h	The difference between supply enthalpy and extract enthalpy
Efficiency of moisture retention	%	The relative efficiency of moisture retention
Efficiency of energy retention	%	The relative efficiency of energy retention