A flue vent connector, used in heating boilers, moves flue or vent gases from the flue collar of the appliance to the chimney or gas vent. Vent connectors sometimes include a device to control drafts.
The connector is not the same thing as a chimney, which moves the gases from the connector to outside. Appliances located in the attic should use Type B or Type L vent connectors, while appliances in the basement can use these connectors, as well as metal or aluminum pipe. If there is more than one vent connector in a vent, chimney or metal pipe, the smaller connector should be higher than the larger one.