IDF Introduction Indirect-fired technologies meet specific customer preferences and are common choices for many commercial, institutional and industrial applications in which the higher capacities, displacement ventilation and fuel efficiency of direct-fired systems are not required. PennBarry’s IDF Series indirect-fired heating and ventilating systems are available in horizontal models for either indoor or outdoor installation. Like most indirect-fired systems, these units are 80% energy efficient and use advanced heat exchangers in the furnace section to provide building supply air at set temperatures. Depending on the application, these systems may be gravity vented or power vented for exhausting combustion gases to the outdoors. | 
