An experimental investigation on convection heat transfer in a confined-jet flow field was conducted for a range of jet diameters and jet Reynolds numbers. The apparatus consisted of a small cylindrical carbon fibre reinforced plastic (CFRP) pressure vessel (0.7 L), a coiled inlet feed tube of variable length and diameter to control the flow of gas into the vessel and a data acquisition system to monitor wall and gas temperatures and pressure during filling of the vessel. The vessel was initially evacuated to a pressure of 1.5 kPa (abs) and then was filled to atmospheric pressure using ambient air. Temperatures and pressures were monitored as the vessel filled and were used to calculate the heat transfer rate. It is found that heat transfer was dominated neither by forced convection nor by free convection heat transfer for the entire filling process. Rather a combination of forced convection, free convection and transient effects were responsible for the observed heat transfer. A correlation for the heat transfer between the gas and the wall of the vessel during filling is proposed.