Selkirk 3" to 4" Increaser (Pellet Vent - VP - Type L)Selkirk 3" to 4" Increaser, 3VP I4 (243304) This gas vent increaser allows you to adapt 3" diameter pipe to 4" diameter pipe when required for your application. Used to adapt 3" pipe to 4" pipe. Pellet Vent VP Type L Model VP's proven coupling design with its built in gasket, connects in seconds and ensures joint integrity. A full line of components increases installation flexibility. 3" to 4" Diameters: Type L Vent Variety of kits available 1"