The Model 4EF3HD Expandable Flex Connector is designed for use with gas-fired appliances equipped with draft hoods and other appliances listed for use with Type B Gas Vent. Single Wall Expandable-Flexible Gas Vent Connector (EFC) offers a simple connection between appliance and Type B vent. UL listed and only requires 1 in. minimum airspace clearance to combustibles and has multiple applications, can be for single vent or combined vent.