The RadonAway XP201c Radon Fan is ideal for most standard radon mitigation jobs and is intended for use as a component of an active soil depressurization (ASD) system for reducing radon. The RadonAway XP201c's unique motor and impeller design makes it one of the most durable general purpose radon mitigation fans on the market. This fan is a good choice for retrofit systems when the sub-slab/sub-membrane material consists of about 4 in. of clean, size 4-6 gravel or moderately loose to moderately tight soil and can be used for slab/membrane sizes up to 1600 sq. ft. The slim, compact, moisture-resistant RadonAway XP201c Radon Fan has a 4 in. duct and can be mounted inside or outside on a 3 in. or 4 in. Sch. 40 PVC vent pipe using 4 in. x 4 in. flexible couplings. NOTE: When installing an ASD system for radon reduction, any openings, major cracks and penetrations in the building slab or membrane must be sealed. Fan sizing for retrofit may require professional diagnostics and design.