The 22DTH-56M is a Belimo active 24V duct humidity and temperature sensor for measuring relative humidity (or absolute humidity / dewpoint / enthalpy — selectable) and temperature in air ducts. The active humidity output is BACnet MS/TP (RS-485) with 0–10V analog backup outputs. The temperature output is active and matches the humidity output type (V or mA). Communicates with the BAS via BACnet MS/TP on RS-485, with 0-10V analog backup outputs preserved for redundancy or for controllers that prefer to read both protocols. The orange UV-resistant polycarbonate housing mounts to the duct exterior; the probe penetrates through a single mounting hole.
Supply, return, and mixed-air duct humidity and temperature monitoring for demand-controlled ventilation, dehumidification staging, dewpoint-based freeze protection, and economizer changeover. Single sensor consolidates two BAS inputs at one duct location.
This SKU communicates with the BAS via BACnet MS/TP over RS-485 as a native BACnet device — all sensor values exposed as BACnet objects, fully discoverable through standard BACnet device discovery. The 0-10V analog backup outputs remain available. BACnet device instance, MS/TP MAC address, and baud rate are configurable via the Belimo Duct Sensor Assistant App.
Key Features
All sensor values and configuration parameters are exposed via BACnet MS/TP over RS-485. Discoverable as a native bus device — no analog scaling, no standalone wiring per signal. Analog 0-10V backup outputs remain available for redundancy or for non-bus consumers.
Configure the humidity output channel to deliver relative humidity, absolute humidity, dew point, or enthalpy via NFC. Default is %RH; change in the field via the Belimo Duct Sensor Assistant App without re-wiring or removing the sensor.
±2% RH accuracy across 0-80% RH at 77°F. Long-term stability ±0.3% RH per year. Stainless steel wire mesh filter protects the polymer element from particulate contamination. 10-second time constant in moving air.
Tap a phone with NFC to the housing to read live values, change output mode, adjust CO2/dewpoint range mappings, set Modbus/BACnet addresses (where applicable), and view diagnostics. The Belimo Duct Sensor Assistant App is free for iOS and Android.
UV-resistant polycarbonate enclosure with NBR70 seal. UL94 5VA flame class and UL 2043 plenum compliant for return-air ducts.
Industry-leading factory warranty backed by Belimo's worldwide service network.
Selectable Humidity Output Modes
The active humidity output channel can be configured to deliver any of four values via NFC and the Belimo Duct Sensor Assistant App. The default is relative humidity (%RH) — change the mode in the field to match your control logic.
| Output Mode | Range | Typical Use |
|---|---|---|
| Relative Humidity (%RH) | 0–100% RH non-condensing | Default — most common BAS humidity input |
| Absolute Humidity | 0–50 g/m³ (default) or 0–80 g/m³ | For dehumidification control, dewpoint-based loads |
| Dew Point | 40–140°F (default) or 0–200°F | For condensation prevention on chilled surfaces |
| Enthalpy | 0–85 kJ/kg | For economizer changeover (energy-based instead of dry-bulb) |
Technical Specifications
| Specification | Detail |
|---|---|
| Sensor Style | Duct Humidity / Temperature Sensor |
| Measured Values | Relative humidity, absolute humidity, dew point, enthalpy, temperature |
| Humidity Sensing Element | Polymer-based capacitive sensor with stainless steel wire mesh filter |
| Humidity Measuring Range | 0–100% RH non-condensing |
| Humidity Accuracy | ±2% RH between 0–80% RH at 77°F (25°C) |
| Humidity Long-Term Stability | ±0.3% RH per year at 70°F (21°C), 50% RH |
| Humidity Time Constant τ (63%) | Typical 10 s @ 3 m/s air velocity |
| Humidity Output | BACnet MS/TP (RS-485) with 0–10V analog backup outputs — min. 10 kΩ load on backup outputs |
| Temperature Sensing Element | Active Pt 1000 (1/3 DIN) |
| Temperature Output | Active BACnet MS/TP (RS-485) with 0–10V analog backup outputs |
| Temperature Measuring Range | -30 to 160°F (-35 to 70°C) |
| Temperature Accuracy | ±0.5°F (±0.3°C) — varies by element, see datasheet for full detail |
| Communication Protocol | BACnet MS/TP |
| Communication Interface | RS-485, half-duplex |
| Bus Configuration | Configurable via NFC / Belimo Duct Sensor Assistant App |
| Analog Backup Outputs | 2× 0-10V (humidity + temperature) — preserved alongside bus communication |
| Default Output Mode (Humidity) | Relative humidity (%RH); change via NFC to absolute / dewpoint / enthalpy |
| NFC Configuration | Yes — Belimo Duct Sensor Assistant App (iOS / Android) |
| Application | Air duct |
| Mounting | Single-hole duct penetration; A-22D-A34 mounting flange and 1/2" NPT conduit adapter included |
| Power Supply | 24 VAC/VDC (19–29 VAC, 15–35 VDC) |
| Power Consumption | 4.3 VA AC / 2.3 W DC |
| Electrical Connection | Pluggable spring-loaded terminal block, max 2.5 mm² |
| Cable Entry | 1/2" NPT conduit adapter included; cable gland with strain relief, ø6...8 mm |
| Housing | UV-resistant polycarbonate, orange — UL94 5VA |
| Enclosure Rating | NEMA 4X / IP65 (UL Enclosure Type 4X), UL 2043 plenum compliant |
| Protection Class | IEC/EN III, SELV; UL Class 2 supply |
| UL Approval | cULus per UL60730-1A/-2-9, CAN/CSA E60730-1/-2-9 |
| Manufacturer | Belimo |
| Manufacturer Part Number | 22DTH-56M |
| Warranty | 5-year factory warranty |
What's In the Box
- 22DTH-56M active humidity + temperature transmitter in orange UV-resistant housing
- A-22D-A34 mounting flange (plastic, up to 248°F / 120°C)
- 1/2" NPT conduit adapter
- Mounting screws and dowels
Documentation
Frequently Asked Questions
What does the 22DTH-56M measure and output?
It measures duct air humidity and temperature and outputs both as analog signals. The humidity output is BACnet MS/TP (RS-485) with 0–10V analog backup outputs; the temperature output is an active analog signal matching the humidity output type. The humidity channel is also configurable via NFC to output absolute humidity, dew point, or enthalpy instead of %RH.
How do I configure the humidity output mode?
Tap an NFC-equipped phone with the Belimo Duct Sensor Assistant App against the housing. The app reads the current configuration, lets you switch the humidity output between %RH, absolute humidity, dew point, or enthalpy, and writes the new configuration back to the sensor — all without removing the sensor or disconnecting wires. Default is %RH. The app is free for iOS and Android.
Why does this SKU have an active temperature output instead of a passive RTD?
This variant ships with both outputs as ACTIVE analog signals — the temperature output matches the humidity output type (BACnet MS/TP). For a PASSIVE RTD temperature output (Pt 1000, Ni 1000 JCI, NTC 10K Type II, NTC 10K Type III, or NTC 20K) instead, choose the appropriate suffix variant — e.g. 22DTH-51MB (Pt 1000), 22DTH-51ML (NTC 10K II). Active outputs are simpler to wire (two signal pairs); passive RTDs are necessary when your controller's temperature input is wired for a specific resistance curve.
Does the BACnet MS/TP version still expose analog outputs?
Yes. The BACnet MS/TP version exposes all sensor values as bus objects AND maintains 2× 0-10V analog backup outputs (humidity + temperature). You can wire the analog outputs as a redundant feed, leave them unconnected, or use them to drive non-bus equipment (e.g. an analog damper actuator) while the BAS reads the bus values. This is useful for migration scenarios where the BAS is bus-native but field equipment is still analog.
How do I configure the BACnet MS/TP address and baud rate?
Use the Belimo Duct Sensor Assistant App via NFC. The app exposes all communication parameters — address, baud rate, parity (Modbus), MAC address (BACnet), device instance (BACnet) — and writes them to the sensor without taking it offline.
What is the difference between humidity, dewpoint, and enthalpy as control inputs?
Relative humidity (%RH) tells you how saturated the air is at its current temperature — the most common input for indoor humidity control and dehumidification. Absolute humidity (g/m³) gives the total moisture content regardless of temperature — useful for mass-balance ventilation calculations. Dewpoint tells you the temperature at which moisture will start condensing — ideal for chilled-surface condensation prevention. Enthalpy (kJ/kg) is the total energy content of the air (sensible + latent) — the preferred input for ASHRAE-compliant economizer changeover, where the comparison should be energy-based rather than dry-bulb-temperature-based. Configure the output to match your control sequence.
Does it need 24V power?
Yes. Power is 24 VAC or 24 VDC. Power consumption is 4.3 VA AC / 2.3 W DC (higher than analog-only variants due to the active bus interface).
- Sensor Type:
- Duct
- Output Signal:
- Humidity + Temperature
- Humidity Output:
- BACnet MS/TP (RS-485) with 0–10V analog backup outputs
- Temperature Output:
- Active analog temperature output (matches humidity output type)
- Power:
- 24 VAC/VDC
- Humidity Element:
- Polymer Capacitive
- Temperature Element:
- Active Transmitter (matches output)
- Selectable Humidity Modes:
- RH / Absolute / Dew Point / Enthalpy
- Default Humidity Mode:
- Relative Humidity (%RH)
- NFC Configuration:
- Yes (Belimo Duct Sensor Assistant App)
- CO2 Element:
- None
- VOC Element:
- None
- Display:
- No Display
- Setpoint:
- No Setpoint
- Override:
- No Override
- Supported Protocols:
- BACnet MS/TP
- Enclosure:
- NEMA 4X Enclosure
