DS18B20 or DHT22: which sensor is better for freeze monitoring?
The DS18B20, for most freeze monitoring. Both are accurate to about ±0.5°C near freezing, but the DS18B20 is sold as a sealed waterproof probe on a cable that you can tape directly to a pipe, and several of them can share one microcontroller pin. Choose the DHT22 when you also want humidity and only need the air temperature of the room.
The numbers
DS18B20: measures −55 to 125°C (−67 to 257°F), ±0.5°C accuracy from −10 to 85°C, runs on 3.0–5.5V, and uses the 1-Wire bus, so multiple probes can share one data pin, each with a unique ID.
DHT22 (AM2302): measures −40 to 80°C at ±0.5°C and humidity from 0–100% at ±2% (±5% worst case), runs on 3.3–5.5V, and should be read no more often than every two seconds.
Why the probe form matters more than the spec
Freeze risk is the temperature at the pipe. A DS18B20 probe on a cable can sit under the pipe insulation in a damp crawlspace while the board stays somewhere dry. A DHT22 is a vented plastic case that measures the air around the board.
With 1-Wire you can run one probe on the pipe and a second in open air from the same pin, which shows how much margin the pipe has.
When the DHT22 is the right pick
Use it where humidity matters as much as cold: a basement, a workshop with tools that rust, or a crawlspace moisture check. Many setups use both: a DS18B20 on the pipe and a DHT22 for the room.
Frequently asked questions
Does the DS18B20 need a resistor?
Yes. The 1-Wire data line needs a pull-up resistor to the supply voltage, commonly 4.7kΩ. Some breakout boards include it.
Are both sensors accurate enough for a freeze alarm?
Yes. Half a degree Celsius is about 1°F, far smaller than the few degrees of margin you should leave between the alert threshold and 32°F.
Related
- ESP32 freeze kit parts list
- Where should a freeze sensor go in a crawlspace?
- How do I build a freeze alert with ESPHome?
Sources
Get a freeze alert for your space
ProbeHarbor watches probes in garages, crawlspaces, and cabins and alerts you before pipes freeze. The free plan includes email alerts; bring an ESP32 probe or connect Home Assistant.