An experimental system consisting a longitudinally finned RT58 phase change material (PCM) in a horizontal cylinder has been conducted to evaluate the heat transfer characteristics of RT58. The investigation forms part of a wider study to investigate a suitable PCM to take advantage of off-peak electricity tariff. The system consisted of a 1.2 m long copper cylinder filled with 93 kg of RT58 with an embedded finned tube at the centre to serve as a heat transfer tube. The experimental data has been reported using hourly temperature profiles, isotherm plots, overall heat transfer coefficients and energy stored. The results show a quadratic relationship between heat transfer coefficient and the inlet HTF temperature within temperature range (62-77 degrees C) investigated. Increasing charge inlet heat transfer fluid temperature by 21.9% increased heat transfer coefficient by 45.3% during charging and 16.6% during discharge. The potential implication of integrating PCM storage system to an air source heat pump to meet 100% residential heating energy load for common buildings in UK has demonstrated that with an improvement in heat transfer, store size can be reduced by up to 30%. (C) 2010 Elsevier B.V. All rights reserved.