Natural convection and radiation heat transfer from annular mounted fins on a horizontal cylinder is studied experimentally and numerically. For experiments, surrounding air temperature is varied 22 degrees C-35 degrees C for fin bases 8 degrees C-15 degrees C. Airflow and thermal boundary layers descend around the fin tube. Heat transfer rates from surfaces of fins and tube base are measured and determined numerically, and good agreement is observed. Results show that cold air starts from the upper point and moves downward and that convection heat transfer is larger than radiation. A new correlation for predicting natural convection heat transfer is developed for the range of measurements.