Calculate Vapor Pressure Deficit - the true drying power of air. VPD combines temperature and humidity into a single number that predicts how fast moisture leaves wood, making it the key control variable for kiln and storage climate.
Vapor Pressure Deficit Calculator
Air temperature in the kiln or store.
Relative humidity of the air (1-100%).
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Vapor Pressure Deficit (VPD) is the difference between how much moisture the air could hold when saturated and how much it actually holds. It is the real driving force that pulls moisture out of wood. Two rooms at the same humidity but different temperatures have very different drying power - VPD captures this in one number, which is why professional kiln and climate control increasingly targets VPD rather than RH alone.