Honeywell AF20-B54 outdoor temperature sensor, NTC 20 kΩ, IP54
- Type: NTC 20 kΩ (25 °C), passive
- Measuring range: -30…+70 °C
- Protection class: IP54
- Mounting: outdoor wall with supplied bracket
Where AF20-B54 is used
This sensor measures outdoor air temperature and delivers it to a Honeywell-family controller, which selects the appropriate supply temperature based on the heating curve. Typical use — substations in multi-family buildings running Honeywell Smile, Excel, or CentraLine controllers. The dome-shaped housing shields the element from direct sunlight and rain, and the mounting bracket keeps a stand-off distance from the wall so the measurement reflects real ambient air, not wall heat.
Technical specifications
| Parameter | Value |
|---|---|
| Code | AF20 (AF20-B54) |
| Manufacturer | Honeywell (Resideo) |
| Sensor type | NTC 20 kΩ (nominal 20 kΩ at 25 °C) |
| Measuring range | -30…+70 °C |
| Accuracy | ±0.2 K at 25 °C (element class) |
| Temperature coefficient | -934.5 Ω/K at 25 °C (non-linear) |
| Connection | 2 terminals, non-polarised |
| Protection class | IP54 |
| Dimensions (L × H × D) | 56 × 81 × 49 mm |
| Mounting | Outdoor wall with supplied bracket |
| Ambient temperature | Matches measuring range (-30…+70 °C) |
| Housing material | UV-resistant plastic |
When to choose AF20-B54
- Retrofit and replacement in existing Honeywell Smile, Excel, CentraLine, Falcon controller systems
- When the original manufacturer signal chain must be preserved without a signal converter
- Substations in multi-family buildings with Honeywell controllers accepting NTC 20 kΩ inputs
- Compatibility: Honeywell Smile SDC, Excel Web/Falcon, CentraLine Merlin/Falcon controllers with NTC 20 kΩ input
B2B delivery and logistics via Amegata.lt
- 24-hour delivery across Lithuania (from our warehouse in Vilnius)
- Competitive B2B pricing — often below market average
- 30-day payment terms for companies (per contract)
- Free technical consultation for sensor compatibility with the existing controller
Official Resideo catalogue: resideo.com/AF20-B54
Frequently asked questions
Is AF20-B54 compatible with Danfoss ECL 210/310?
No. The Danfoss ECL series uses a Pt 1000 element (platinum, 1 kΩ at 0 °C), while the AF20-B54 is NTC 20 kΩ. The characteristics differ and the controller will read a wrong temperature. Use the Danfoss ESMT sensor (SKU 084N1012) for ECL systems.
Where should the outdoor sensor be mounted?
On the north or northwest side of the building, around 2.5 m above ground, at least 30 cm away from windows, vents, and heat sources. Avoid direct sunlight and chimney plumes — otherwise the heating curve will compensate a "false" temperature.
How far can the cable be extended?
The NTC 20 kΩ signal is resistant to conductor resistance, so up to ~50 m of 2 × 0.75 mm² shielded cable can be used without error. When routing through trenches, ground the shield only at one end (at the controller) — dual grounding creates a noise loop.
Does it need calibration?
No — the NTC 20 kΩ element is factory-calibrated to ±0.2 K at 25 °C. At -20 °C outdoors, natural element deviation is under 1 K, which is not critical for the heating curve. Calibration is only needed if sensor damage is suspected.
What's the difference between AF20-B54 and SF20-B54?
AF20 — outdoor air sensor with dome-shaped protective housing. SF20 — surface sensor for pipe mounting with strap and clamp. Although both use the same NTC 20 kΩ element internally, the housing and mounting differ — not directly interchangeable.
