Drying Equipment in Water Damage Restoration

Drying equipment forms the operational core of any structural drying project, determining how quickly moisture is removed from building materials and how effectively secondary damage — including mold growth — is prevented. This page covers the primary equipment categories used in professional water damage restoration, how each class functions at a mechanical level, the scenarios that drive equipment selection, and the decision thresholds that govern deployment. Understanding equipment classification is essential for interpreting scope-of-work documents, insurance claim line items, and compliance with IICRC standards for restoration.

Definition and scope

Drying equipment in water damage restoration refers to the mechanical and electromechanical systems deployed to extract liquid water, remove water vapor from air, and drive evaporative drying of structural assemblies such as subfloors, wall cavities, and ceiling systems. Equipment deployment is governed by the Institute of Inspection, Cleaning and Restoration Certification (IICRC) Standard S500, Standard for Professional Water Damage Restoration, which classifies water damage into four categories of loss and four water damage classes that directly dictate equipment type and quantity.

The scope of drying equipment extends beyond portable units placed on a job site. It includes desiccant systems, injection drying tools, and structural cavity drying attachments. Documentation of equipment placement, airflow configuration, and daily moisture readings is required under IICRC S500 and expected by insurance carriers during claim review. The water damage restoration services process treats equipment selection as a technical decision, not an arbitrary one — underpowering a drying system extends drying time and increases the probability of microbial amplification under conditions that IICRC S520 identifies as the threshold for mold remediation intervention.

How it works

Structural drying operates through three simultaneous physical processes: evaporation (converting liquid water in materials into vapor), dehumidification (removing that vapor from the air), and airflow (accelerating surface evaporation by replacing humid air at material surfaces with drier air). Each equipment category addresses one or more of these processes.

Air movers (axial and centrifugal fans)
Air movers generate high-velocity airflow across wet surfaces. Centrifugal air movers produce a focused, high-pressure airstream suited for directing into wall cavities or beneath floating floors. Axial air movers move larger volumes of air at lower pressure and are used for open-floor surface drying. IICRC S500 guidance specifies one air mover per 50–70 square feet of wet surface area as a baseline deployment ratio, though actual placement is adjusted by moisture readings from moisture mapping protocols.

Refrigerant dehumidifiers (LGR and conventional)
Low-grain refrigerant (LGR) dehumidifiers operate efficiently at low grain levels — typically below 40 grains per pound of air — which is the operating range that matters once initial bulk moisture has been extracted. Conventional refrigerant dehumidifiers become less effective below 55°F and remove less moisture per kilowatt-hour than LGR units under drier conditions. LGR units can remove 25–30 percent more moisture per energy unit than conventional refrigerant models at equivalent grain levels, making them the preferred class for most residential and commercial structural drying.

Desiccant dehumidifiers
Desiccant systems use a hygroscopic rotor (typically silica gel or lithium chloride) to adsorb moisture from process air. Unlike refrigerant units, desiccant dehumidifiers maintain high moisture removal capacity at temperatures below 40°F and at very low relative humidity levels. They are deployed in freezing environments, large commercial structures, and situations requiring aggressive drying of dense materials such as concrete or masonry. Desiccant units require a regeneration air exhaust routed to the exterior.

Extraction equipment
Truck-mounted and portable extraction units remove standing and absorbed liquid water before evaporative drying begins. Weighted extraction tools (water claws) applied to carpet and padding can remove approximately 90 percent of absorbed water from carpet systems before the pad requires replacement.

Common scenarios

Category 1 / Class 2 residential loss — A supply line failure saturates a single room's hardwood floor and adjacent drywall. Deployment typically involves 4–6 centrifugal air movers, 1–2 LGR dehumidifiers, and floor mat drying systems injected beneath the flooring.
Category 3 / Class 3 loss — A sewage backup or flood damage event saturates wall cavities and subfloor assemblies across multiple rooms. Cavity drying requires drilled injection ports and positive-pressure drying attachments combined with LGR or desiccant dehumidification.
Commercial large-loss events — A roof failure saturating 10,000 square feet of a warehouse or office building requires trailer-mounted desiccant systems supplemented by portable LGR units, with thermal imaging used to identify hidden wet assemblies.
Low-temperature environments — Drying a structure during winter in an unheated space requires desiccant deployment because refrigerant dehumidifiers cease effective operation below 45°F.

Decision boundaries

Equipment selection is not arbitrary. IICRC S500 defines decision thresholds that govern when equipment classes are substituted or supplemented:

Class of water damage (1 through 4) determines the ratio of air movers to dehumidifiers and whether desiccant augmentation is required.
Grain per pound (GPF) readings drive the switch from conventional refrigerant to LGR units; LGR equipment is indicated when GPF drops below 65.
Ambient temperature below 45°F disqualifies standard refrigerant dehumidifiers and triggers desiccant deployment.
Material porosity (IICRC S500 classifies materials into three porosity categories) governs whether injection drying is required in addition to surface airflow.
Psychrometric calculations — derived from temperature, relative humidity, and specific humidity readings — determine daily equipment adjustments and the drying goal (typically a return to pre-loss equilibrium moisture content for the specific material type).

Monitoring is performed daily using calibrated thermo-hygrometers and pin-type or pin-less moisture meters. Drying is not considered complete until materials reach their regional equilibrium moisture content (EMC), a threshold referenced in IICRC S500 and verifiable against USDA Forest Products Laboratory EMC tables. Restoration services documentation practices require that all readings, equipment serial numbers, and placement logs be retained as part of the project file.