Combustion Air Intake System For Fuel Type Natural Gas and Oil Maximum Appliance BtuH Input 2 500 000 BtuH Maximum Airflow 680 cfm Nameplate Voltage 120V AC Compatible System 120V Appliance 24V Gas Appliance 750 mV Gas Appliance Inlet Diameter 10 in Outlet Diameter 10 in Oil Appliance BtuH Input Up to 2 300 000 BtuH Natural Gas Appliance BtuH Input 1 300 000 BtuH Minimum Vent Pipe Diameter 10 in Maximum Vent Pipe Diameter 10 in For Maximum Duct Length 100 ft