Using A Hygrometer

In wintertime, the cool, crisp conditions will likely alter the environment inside your humidor. In summertime, the hot, humid weather can drive you crazy adjusting the humidity levels. So, you’ll want to keep a close eye on your humidor.

But how do you know that your hygrometer is reading the humidity accurately? A simple calibration will do the trick. Here are a couple of ways to calibrate your hygrometer!

Salt Test for Digital Hygrometers

The act of measuring humidity is relative. Digital hygrometers will typically be accurate within 2 or 3 percentage points. Here is how to determine whether the accuracy of your display is within the acceptable range. Raoult’s Law and Henry’s Law, which have been known for more than 100 years, state that a saturated salt solution in water will contain a constant level of relative humidity in an enclosed chamber.

1. In a bottle cap or small container, combine both salt and water to make a paste.
2. Place your hygrometer and the salt paste into a zip lock baggie for 24-36 hours.
3. The environment inside will be 75.5 percent humidity — the natural level maintained by salt when dampened and put in an enclosed environment — and your hygrometer should read this within plus or minus 3 percentage points. If it reads differently, make a note and factor it in to future humidor readings.
4. After 8 hours in the damp salt environment, the actual humidity inside the bag will be 75%.
5. Compare it to your hygrometer, your hygrometer should also read 75%. If not, you will then know exactly how far off your hygrometer is. If it’s off, note the amount and direction that it actually reads and be sure to add or subtract that amount when reading the hygrometer.
6. If the hygrometer has a control to adjust the display you can set the hygrometer to 75% immediately after the test.

You should salt test your hygrometer every 6 months or so to be sure of the accuracy.

We recommend buying a digital hygrometer ALWAYS, as analog hygrometers can be off as much as 20 – 30%!

Towel Test for Analog Hygrometers:

If you do choose to use an analog hygrometer, you can dampen a towel (not dripping wet, but good and damp), then wrap the hygrometer in the towel for 30 to 45 minutes. After this time, unwrap it and read the humidity (quickly). If your hygrometer is perfectly calibrated (few are) it will be reading exactly 100% humidity. Most likely, it will be reading somewhere between 80 and 90%. At this point, whatever the hygrometer reads, you can either set the needle to exactly 100% immediately after the test. Replace the hygrometer in your humidor and allow 6 hours for the unit to reset.