Communication fails after wiring. What should I check first?

Verify the baud rate is set to 115200 on both the gateway and the HRU-P unit. Also confirm that the RS-485 A and B lines are not swapped and that a common GND connection is present.

Which wiring diagram should I use for my model?

HRU-SlimAIR-P, HRU-PremAIR-P, and HRU-MinistAIR-P models share one PCB connection structure. HRU-FlatAIR-P models use a different layout. Check the Alnor installation documentation for the correct pinout before connecting.

Can I connect multiple HRU-P units on the same RS-485 bus?

Yes, as long as each unit has a unique Modbus slave address. Make sure the total cable length and number of devices stay within RS-485 bus limits, and add a termination resistor at the end of the bus if needed.

Some sensor readings show zero or are missing. Why?

Not all HRU-P models include internal humidity or CO2 sensors. If a sensor is not physically present in the unit, the corresponding register will return zero or a default value. Confirm the sensor configuration of your specific model.

Free Modbus template: Alnor HRU-P

Name: Alnor HRU-P
Brand: Alnor Systemy Wentylacji Sp. z o. o.
SKU: 57f1c89f-9735-41a7-be64-84c40a0bcc42

This template monitors and controls Alnor HRU-P heat recovery ventilation units via Modbus RTU at 115200 baud. It reads temperatures, fan speeds, airflow, humidity, CO2, filter status, and bypass position. It also provides write access for work mode selection, fan speed and airflow settings, bypass control, and GHE configuration.

Registers (49)

49 read / 23 write

Name	Address	Function	Type	Unit	Access
Error Status (R) Device failure signaling	3	FC03	uint16		R
Work Mode (RW) Read current work mode of the unit	4	FC03	uint16		R/W
Exhaust temperature sensor (R) Exhaust temperature sensor	9	FC03	int16	°C	R
Extract temperature sensor (R) Extract temperature sensor	7	FC03	uint16	°C	R
Inlet temperature sensor (R) Inlet temperature sensor	8	FC03	uint16	°C	R
Supply temperature sensor (R) Supply temperature sensor	6	FC03	uint16	°C	R
Pre-heater thermostat (R) 0 - open contact 1 - contact closed	15	FC03	uint16		R
Afterheater thermostat (R) 0 - open contact 1 - contact closed	16	FC03	uint16		R
Bypass status (R) 0 - ON, 1 - OFF	17	FC03	uint16		R
SAP signal (R) 0 - SAP 1 -NO SAP	18	FC03	uint16		R
Pre-heater status (R) 0 - Inactive 1 - Active	22	FC03	uint16		R
Afterhater status (R) 0 - Inactive 1 - Active	23	FC03	uint16		R
Bypass position (R)	27	FC03	uint16	%	R
Time Mode OUT (RW) 0 - Inactive 1 - Active	33	FC03	uint16		R/W
Time Mode PARTY (RW) 0 - Inactive 1 - Active	34	FC03	uint16		R/W
Fireplace Mode (RW) 0 - Inactive 1 - Active	35	FC03	uint16		R/W
Supply fan speed (R) Supply fan speed	43	FC03	uint16	%	R
Exhaust fan speed (R) Exhaust fan speed	44	FC03	uint16	%	R
Supply fan speed - Speed 1 (RW)	48	FC03	uint16	%	R/W
Supply fan speed - Speed 2 (RW)	49	FC03	uint16	%	R/W
Supply fan speed - Speed 3 (RW)	50	FC03	uint16	%	R/W
Exhaust fan speed - Speed 2 (RW)	55	FC03	uint16	%	R/W
Exhaust fan speed - Speed 3 (RW)	56	FC03	uint16	%	R/W
Exhaust fan speed - Speed 1 (RW)	54	FC03	uint16	%	R/W
Flow setpoint supply (R)	98	FC03	uint16	m³/h	R
Supply fan flow - Speed 2 (RW)	109	FC03	uint16	m³/h	R/W
Flow setpoint exhaust (R) W zależnosci od modelu rekuperacji ...	99	FC03	uint16	m³/h	R
Flow reading supply (R) Flow reading supply	94	FC03	uint16	m³/h	R
Flow reading exhaust (R) Flow reading exhaust	95	FC03	uint16	m³/h	R
Supply fan flow - Speed 1 (RW)	108	FC03	uint16	m³/h	R/W
Supply fan flow - Speed 3 (RW)	110	FC03	uint16	m³/h	R/W
Exhaust fan flow - Speed 1 (RW)	112	FC03	uint16	m³/h	R/W
Exhaust fan flow - Speed 2 (RW)	113	FC03	uint16	m³/h	R/W
Exhaust fan flow - Speed 3 (RW)	114	FC03	uint16	m³/h	R/W
GHE status (R) 0 - Inactive 1 - Active	26	FC03	uint16		R
GHE mode (RW) 0 - closed, 1 - open, 2 - auto	69	FC03	uint16		R/W
GHE winter temperature (RW)	70	FC03	uint16	°C	R/W
GHE summer temperature (RW)	71	FC03	uint16	°C	R/W
Filter alarm (R) 0 - Inactive 1 - Active	202	FC03	uint16		R
Turn ON/OFF (RW) 0 - OFF, 1 - ON	1	FC03	uint16		R/W
Supply filter days left (R)	84	FC03	uint16	days	R
Exhaust filter days left (R)	85	FC03	uint16	days	R
Supply air filter - depletion (R) Supply air filter - depletion	86	FC03	uint16	%	R
Exhaust air filter - depletion (R) Exhaust air filter - depletion	87	FC03	uint16	%	R
Reset filter counting (RW) 2 - Only supply filter, 3 - Only exhaust filter, 7 - Both filters	88	FC03	uint16		R/W
Bypass control (RW) 1 - Closed, 2 - Open, 3 - AUTO	89	FC03	uint16		R/W
Airing time mode (RW) 0 - Inactive 1 - Active	32	FC03	uint16		R/W
Humidity indoor (R)	41	FC03	uint16	%	R
CO2 indoor (R)	42	FC03	uint16	ppm	R

Specifications

Protocol

Modbus RTU

Brand

Alnor Systemy Wentylacji Sp. z o. o.

Registers

Compatible models

HRU-SlimAIR-250-H-PHRU-SlimAIR-250-H-CF-PHRU-SlimAIR-250E-H-PHRU-SlimAIR-250E-H-CF-PHRU-SlimAIR-L-250-H-PHRU-SlimAIR-L-250-H-CF-PHRU-SlimAIR-L-250E-H-PHRU-SlimAIR-L-250E-H-CF-PHRU-SlimAIR-350-H-PHRU-SlimAIR-350-H-CF-PHRU-SlimAIR-350E-H-PHRU-SlimAIR-350E-H-CF-PHRU-SlimAIR-400-H-PHRU-SlimAIR-400-H-CF-PHRU-SlimAIR-400E-H-PHRU-SlimAIR-400E-H-CF-PHRU-SlimAIR-300-H-PHRU-SlimAIR-300-H-CF-PHRU-SlimAIR-300E-H-PHRU-SlimAIR-300E-H-CF-PHRU-SlimAIR-500-H-PHRU-SlimAIR-500-H-CF-PHRU-SlimAIR-500E-H-PHRU-SlimAIR-500E-H-CF-PHRU-SlimAIR-800-H-PHRU-SlimAIR-800-H-CF-PHRU-SlimAIR-800E-H-PHRU-SlimAIR-800E-H-CF-PHRU-SlimAIR-1000-PHRU-SlimAIR-1000E-PHRU-SlimAIR-1000E-CF-PHRU-SlimAIR-1000-CF-PHRU-PremAIR-350-PHRU-PremAIR-350-CF-PHRU-PremAIR-350E-CF-PHRU-PremAIR-350E-PHRU-PremAIR-450-PHRU-PremAIR-450-CF-PHRU-PremAIR-450E-PHRU-PremAIR-450E-CF-PHRU-PremAIR-500-PHRU-PremAIR-500-CF-PHRU-MinistAIR-L-250E-H-CF-PHRU-MinistAIR-L-250E-H-PHRU-MinistAIR-L-250-H-CF-PHRU-MinistAIR-L-250-H-PHRU-MinistAIR-L-325E-H-CF-PHRU-MinistAIR-L-325E-H-PHRU-MinistAIR-L-325-H-CF-PHRU-MinistAIR-L-325-H-PHRU-MinistAIR-L-350E-H-CF-PHRU-MinistAIR-L-350E-H-PHRU-MinistAIR-L-350-H-CF-PHRU-MinistAIR-L-350-H-PHRU-MinistAIR-LS-250E-H-CF-PHRU-MinistAIR-LS-250E-H-PHRU-MinistAIR-LS-250-H-CF-PHRU-MinistAIR-LS-250-H-PHRU-MinistAIR-LS-325E-H-CF-PHRU-MinistAIR-LS-325E-H-PHRU-MinistAIR-LS-325-H-CF-PHRU-MinistAIR-LS-325-H-PHRU-MinistAIR-LS-350E-H-CF-PHRU-MinistAIR-LS-350E-H-PHRU-MinistAIR-LS-350-H-CF-PHRU-MinistAIR-LS-350-H-PHRU-MinistAIR-R-250E-H-CF-PHRU-MinistAIR-R-250E-H-PHRU-MinistAIR-R-250-H-CF-PHRU-MinistAIR-R-250-H-PHRU-MinistAIR-R-325E-H-CF-PHRU-MinistAIR-R-325E-H-PHRU-MinistAIR-R-325-H-CF-PHRU-MinistAIR-R-325-H-PHRU-MinistAIR-R-350E-H-CF-PHRU-MinistAIR-R-350E-H-PHRU-MinistAIR-R-350-H-CF-PHRU-MinistAIR-R-350-H-PHRU-MinistAIR-RS-250E-H-CF-PHRU-MinistAIR-RS-250E-H-PHRU-MinistAIR-RS-250-H-CF-PHRU-MinistAIR-RS-250-H-PHRU-MinistAIR-RS-325E-H-CF-PHRU-MinistAIR-RS-325E-H-PHRU-MinistAIR-RS-325-H-CF-PHRU-MinistAIR-RS-325-H-PHRU-MinistAIR-RS-350E-H-CF-PHRU-MinistAIR-RS-350E-H-PHRU-MinistAIR-RS-350-H-CF-PHRU-MinistAIR-RS-350-H-PHRU-FlatAIR-80E-H-PHRU-FlatAIR-80E-H-CF-PHRU-FlatAIR-80-H-PHRU-FlatAIR-80-H-CF-PHRU-FlatAIR-100E-H-PHRU-FlatAIR-100E-H-CF-PHRU-FlatAIR-100-H-PHRU-FlatAIR-100-H-CF-PHRU-FlatAIR-120E-H-PHRU-FlatAIR-120E-H-CF-PHRU-FlatAIR-120-H-PHRU-FlatAIR-120-H-CF-PHRU-FlatAIR-125E-H-PHRU-FlatAIR-125E-H-CF-PHRU-FlatAIR-125-H-PHRU-FlatAIR-125-H-CF-PHRU-FlatAIR-150E-H-PHRU-FlatAIR-150E-H-CF-PHRU-FlatAIR-150-H-PHRU-FlatAIR-150-H-CF-PHRU-FlatAIR-200E-H-PHRU-FlatAIR-200E-H-CF-PHRU-FlatAIR-200-H-PHRU-FlatAIR-200-H-CF-PHRU-FlatAIR-225E-H-PHRU-FlatAIR-225E-H-CF-PHRU-FlatAIR-225-H-PHRU-FlatAIR-225-H-CF-PHRU-FlatAIR-250E-H-PHRU-FlatAIR-250E-H-CF-PHRU-FlatAIR-250-H-PHRU-FlatAIR-250-H-CF-P

Last updated

2 April 2026

Alnor HRU-P

Overview

Key readings

Available commands

Use cases

Installation

Things to watch for

Registers (49)

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