The AprilAire ARNTF4 Transition Fitting consolidates the number of fittings needed in outdoor radon mitigation system installations. The Transition Fitting connects a 4" fan pipe to a 4" exhaust pipe with a weir (not included) for capturing and draining condensate. Weir is included in the ARNCBK Condensate Bypass Kit. *Please note contractor must be certified to buy/sell radon products.