Thermometers & Hygrometers

Which grow-room monitor fits?

Guessing is worse than any thermo-hygrometer, but the units on this page do different jobs. The split is whether they log history, whether they alert you when conditions drift, and whether they measure the air or the leaf.

Basic digital thermo-hygrometers

These put a live temperature and humidity reading on a tent-mounted screen, and most keep a max/min memory so overnight highs and lows are still there in the morning. Cultiv8, Essentials Digital Max Min, Bloom Works and Grow Kings all sit in this band. One tent you walk past every day rarely needs more.

App-connected sensors

Readings go to your phone on a continuous log, which is the point when you are not in the room every hour. AC Infinity Cloudcom A1 and B2 join the UIS controller ecosystem; Vivosun Aerolab is Bluetooth; Pulse One is a standalone environmental monitor. History is the feature — the 3am humidity spike shows up instead of disappearing while you sleep.

VPD and infrared

Vapour pressure deficit is a leaf-temperature number, and under most lights the leaf sits cooler than the air. The AC Infinity VPD thermometer takes that leaf reading and calculates VPD from it. Infrared guns such as the Hydroaxis unit give you surface temperature on demand, which is how you find a hot patch under a light or a cold spot near an intake.

Where the sensor should sit

1. At canopy height. Skip the floor and skip the roof clip. The plant lives at the top of the canopy, so that is the air that matters.
2. Away from direct light. Sit a sensor in the beam and it reports its own heat, not the room. Park it at the same height, just outside the light footprint.
3. Away from the intake and the humidifier. Moving air or mist is that device talking, not the room average.
4. Use two if the room is large. Several degrees can sit between corners of a big room. A single mid-room reading hides the spread.

The reading is only the first step. The kit that acts on it is in humidifiers, dehumidifiers and fans and blowers.