Tjernlund in-line draft inducers assure positive draft when restricted boilers and furnaces, poor chimneys or negative pressures in buildings prevent proper exhaust of combustion gases. The venturi action starts air moving up the stack instantly & keeps it moving smoothly. These units are quick and easy to install and completely automatic in operation. In-line draft inducers are built for long-lasting, trouble-free service and available in sizes and capacities to meet virtually all heating system requirements. The Vari-Draft control permits adjustment to individual job requirements.