What may a restorer consider when the outside humidity ratio is significantly lower than indoors,...

The IICRC WRT body of knowledge explains that whenoutdoor humidity ratio is significantly lower than indoor humidity ratio, and outdoor temperature is equal to or higher than indoor temperature, a restorer may consider using anopen drying system.

An open drying system introduces outside air to replace moist indoor air, reducing the indoor humidity ratio and vapor pressure. When the incoming air is warmer and drier, it enhances evaporation and supports moisture removal without relying solely on mechanical dehumidification.

The WRT manual stresses that ventilation decisions must be based on psychrometric comparison—not assumptions about comfort. Using outside air under favorable conditions can be energy-efficient and effective, but only when conditions are continuously monitored.

A closed system would be counterproductive in this scenario, as it would trap higher-moisture air inside the drying chamber. Increasing indoor humidity or expecting reduced evaporation contradicts drying physics.