Guide
What humidity level to hold, and why 50% is the usual answer
Most guidance lands on 45% to 55% relative humidity. Below that you are spending money to dry wood that does not need drying. Above 60% you are in the range where mould grows.
The bands that matter
| Reading | What it means |
|---|---|
| Under 40% | Drier than needed. Wood shrinks, and you are paying for it. |
| 45 to 55% | The target band. Mould does not get going here. |
| 55 to 60% | Acceptable in summer in a humid climate. Watch it. |
| Over 60% | Mould territory. Sustained readings here are the reason to buy. |
| Over 70% | Dust mites and rot as well as mould. Act now. |
Set the humidistat, not the timer
A dehumidifier on a timer runs when the clock says so, not when the air needs it. A humidistat runs it when the reading drifts above the setpoint, which is both cheaper and more effective. Every unit worth buying has one.
See AlorAir crawl space and basement units
Where to put the sensor
Not next to the unit's own outlet, where it reads the dry air it just made and shuts off early. Put it at the far end of the space, at roughly the height you care about, and leave it there long enough to see a pattern.
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See AlorAir crawl space and basement units