The 22DTH-51M 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 0–5V or 0–10V (jumper-selectable). The temperature output is active and matches the humidity output type (V or mA). 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.
Key Features
Two independent active analog outputs (0–5/10V on both channels) for humidity and temperature. Wire each to its own BAS input — reduces parts count and conduit pulls vs separate hum and temp sensors at the same location.
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 | 0–5V or 0–10V (jumper-selectable) — min. 10 kΩ load resistance |
| Temperature Sensing Element | Active Pt 1000 (1/3 DIN) |
| Temperature Output | Active 0–5V or 0–10V (jumper-selectable) |
| 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 |
| 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 (21.6–26.4 VAC, 13.5–26.4 VDC) |
| Power Consumption | 0.8 VA AC / 0.4 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-51M |
| Warranty | 5-year factory warranty |
What's In the Box
- 22DTH-51M 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-51M measure and output?
It measures duct air humidity and temperature and outputs both as analog signals. The humidity output is 0–5V or 0–10V (jumper-selectable); 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 (0–5/10V). 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.
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 0.8 VA AC / 0.4 W DC.
- Sensor Type:
- Duct
- Output Signal:
- Humidity + Temperature
- Humidity Output:
- 0–5V or 0–10V (jumper-selectable)
- 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:
- None (analog)
- Enclosure:
- NEMA 4X Enclosure
