In-vessel retention is a key severe accident management strategy now being adopted by some nuclear power plants which has been proposed for some advanced light water reactors. Saturated pool boiling heat transfer coefficients and the critical heat flux (CHF) were measured from three downward facing pin fin surfaces in deionized water with the fins added to enhance the CHF. The inclination angles were 5 degrees, 30 degrees, 45 degrees, 60 degrees and 90 degrees (vertical). The results show that the nucleate boiling heat transfer coefficients and the local CHF for the pin fin surfaces were consistently higher than those for a plain surface. The enhancements of the local CHF and the nucleate boiling heat transfer coefficients were mainly due to the pin fins that effectively provide sufficient liquid to the vaporization sites on the heated surfaces, reduce the wall temperature and delay the boiling crisis. The CHF of the pin fin surface with a fin length of 1 mm, a fin width of 1 mm, a fin height of 2 mm, and a fin spacing of 2 mm, were the best with more than 200% CHF enhancements at all inclination angles. The CHF of the pin fin surface increases as the number of fins per unit area increases and even more as the fin height increases. (C) 2015 Elsevier Ltd. All rights reserved.