Which drying system creates the lowest vapor pressure?

The IICRC WRT body of knowledge identifiesdesiccant dehumidification systemsas capable of creating thelowest vapor pressurein a drying environment. Desiccant systems remove moisture through adsorption, allowing them to achieve extremely low humidity ratios and vapor pressures—lower than refrigerant-based systems can typically reach.

Because vapor pressure drives moisture movement, achieving very low air vapor pressure significantly increases the drying potential for dense or low-permeance materials. This is why desiccant systems are often specified for Class 4 drying, cold environments, or situations requiring aggressive moisture removal.

Heat-only systems increase vapor pressure unless paired with moisture removal. Inter-air systems enhance airflow but do not independently reduce vapor pressure. LGR dehumidifiers reduce vapor pressure effectively but not to the same extent as desiccants.

The WRT curriculum emphasizes that system selection must be based on drying objectives and material characteristics, with desiccants reserved for scenarios requiring maximum vapor pressure reduction.