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How to use a humidity meter

Set up a repeatable room-humidity check and avoid misleading sensor positions.

By Dehumidifier UK · Updated 6 October 2026 · Sources linked below

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Our answer

Place the meter away from direct heat, sunlight, a wet window and a dehumidifier’s dry-air outlet. Give it time to settle after moving it, then record temperature and RH at consistent times. Interpret the trend and the device’s accuracy rather than act on every one-point change.

Set up your first readings

  1. Check the battery, display units and any protective film or packaging. Read the sensor’s manual.
  2. Choose a representative position in the room with air able to reach the sensor.
  3. Let the instrument settle for the time its manufacturer specifies. Do not use the first reading after bringing it in from a cold delivery van.
  4. Record RH, temperature, time and room. Note cooking, laundry, showers, ventilation and heating.
  5. Repeat over several days before deciding whether the usual pattern has improved.

What to write down

FieldWhy it matters
Temperature and RHAn RH fall after heating may not mean moisture has been removed.
Time and activitySeparates a shower spike from a persistent elevated reading.
Sensor positionDry outlet air and cold glass can distort the room comparison.
Visible symptomsCondensation or mould can matter even when a room-average reading looks ordinary.

Two meters do not have to match exactly

A stated ±3 percentage-point accuracy means a display of 60% can correspond to roughly 57–63% within the specified conditions. A second sensor has its own uncertainty. Compare meters side by side after they settle before attributing a difference to the room, and do not calibrate one to the other without a valid reference method.

Min/max memory and logging

Reset min/max memory at a consistent time if you want day-to-day comparisons. For a logger, check its sampling interval, time zone and whether history remains available when it is out of Bluetooth range. A connected sensor does not necessarily offer remote access unless a compatible hub is present.

What the readings cannot establish

A room-air sensor cannot tell you the moisture content of plaster or prove why a wall is damp. Use readings alongside the building symptoms and a sensible source-control routine. Our humidity meter shortlist explains device choices; the humidity guide explains what the numbers mean.

Sources and evidence

  1. SwitchBot Meter Plus UK specifications
  2. TFA EXACTO 30.5047
  3. TFA 30.5027 thermo-hygrometer
  4. GOV.UK: addressing damp and mould in homes
  5. Dartford Borough Council: damp, mould and condensation

Sources checked 6 October 2026. Manufacturer specifications are claims under their stated conditions; they are not our household measurements.