Thermal and pressure drop performance data are given on slotted-fin heat exchanger. Measurements were made using up to 7000 lbhr of exhaust gas and up to 5000 lbhr ventilating air. Inlet exhaust gas temperature was maintained at 1400 deg F, and that of the ventilating air was 95 deg F. Three different cross-flow air shrouds were used in tests. Thermal output of heater was determined by enthalpy changes of ventilating air. Maximum measured rate of heat transfer was 216,000 BTU per hour.