DTH–DTHR products are available in two versions, “ETL listed” (DTH model) and “ETL recognized” (DTHR model). Both versions deliver the same outstanding performance and unparalleled turndown. Depending on the output of the selected unit, the turndown ratio varies from 15:1 to 31:1. The DTH unit can also be used as a duct heater, with the fan installed upstream of the heat exchanger.