The Rn4 features an electronically commutated (EC) motor. Inherently efficient and operationally stable at full and reduced speeds, the EC motor arms the radon professional with installation methods not previously practical. Located in the wiring box, an integral speed control potentiometer can be used to “dial in” the fan speed necessary to achieve either the required sub-slab depressurization or required system air flow rate. For demand-controlled systems, the potentiometer can be removed from the wiring terminal block to accommodate an externally-provided 0-10Vdc speed command. The Rn4 series fans are constructed with UL certified, UV protected Polycarbonate material that are vibration welded for 100% leak-proof housing construction. Totally enclosed motors are designed with extra moisture protection for radon application. The Rn4 also features a housing produced via a vibration welding process. Without relying on fasteners or sealant, the process results in a fused seam that is strong, permanent and inherently air tight.