Most consumer-grade hygrometers, including brands like Unni, ThermoPro, Govee, and Veanic, are not reliable enough for monitoring the humidity around a valuable instrument like a piano. These devices often claim ±5% RH accuracy, but real-world testing frequently shows fluctuations of 10% or more. This means your hygrometer might be telling you it’s 40% humidity, when it’s actually barely 30%!
In the cover photo for this article, you can see an Unni hygrometer reading 34% next to a more accurate Reed device reading 25.4%. If you looked at the Unni, you might think the humidity was a bit low. However, according to the Reed, the situation is much worse! And inexpensive hygrometers only get less accurate the more extreme the humidity gets, which makes it even harder to get an accurate idea.
Using an inexpensive hygrometer can create a false sense of security. They wrongly reassure you that your instrument is safe when, in reality, conditions are much worse. Low humidity risks soundboard cracks, while high humidity risks swelling, mold sticking keys.
Many of these hygrometers lack proper factory calibration and cannot be recalibrated, meaning any inaccuracies out of the box or sensor drift over time cannot be corrected. Additionally, their sensors tend to be slow to respond to environmental changes and may suffer from hysteresis, where they fail to return to accurate readings after large humidity fluctuations. This means that even if they read correctly one day, they may be significantly off the next.
Beyond accuracy issues, these low-cost hygrometers are frequently poorly constructed, with cheap plastic casings, low-quality sensors, and short lifespans. Many models degrade over time, leading to even greater inaccuracy! Their batteries may drain quickly due to inefficient power design.
Oasis OH-2 Hygrometer
I recommend these to customers regularly. They’re still fairly inexpensive (about $30), but are considerably more accurate than the majority of consumer hygrometers. You can purchase them directly from Oasis or from Sweetwater.
Testo 602-H1 Hygrometer
This is definitely the most expensive option, but it’s extremely accurate. They also have the 602-H2, which includes a visible flashing alarm when the humidity is outside the desired range. You can order the Testo 602-H1 Hygrometer directly from Testo.
