Ultimately, it is difficult to calculate how long it will take to dehumidify your crawl space as a result of dehumidifier efficiency changing based on the environment. For example, the Alorair 70 Pint Dehumidifier will take a full 70 pints of water out of the air every day at 90 degrees Fahrenheit and 90 percent RH, but only 35 pints per day at 80 degrees Fahrenheit and 60 percent RH. Dehumidifiers are best used for the long haul, not as a one-off.